GSEB Class 10 Science Solutions Chapter 13 Magnetic Effects of Electric Current

Question 1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Answer: (d) The field consists of concentric circles centred on the wire.
In simple words: For a long, straight wire carrying electric current, the magnetic field lines form circles around the wire, with the wire at the middle.

Exam Tip: Remember the right-hand thumb rule to easily visualize the direction of magnetic field lines around a straight current-carrying conductor.

Question 2. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating a magnetic field due to current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Answer: (c) producing induced current in a coil due to relative motion between a magnet and the coil.
In simple words: Electromagnetic induction is when a current appears in a wire coil because a magnet is moved near it, or the coil moves near a magnet.

Exam Tip: Understand that electromagnetic induction requires relative motion between the conductor and the magnetic field; a stationary magnet and coil will not induce current.

Question 3. The device used for producing electric current is called a
(a) generator
(b) galvanometer.
(c) ammeter
(d) motor.
Answer: (a) generator
In simple words: A generator is a machine that makes electric current.

Exam Tip: A generator makes electricity, an ammeter measures current, a galvanometer detects small currents, and a motor turns electricity into motion.

Question 4. The essential difference between an AC generator and a DC generator is that
(c) AC generator will generate a higher voltage.
(d) AC generator has split rings while the DC generator has a commutator.
Answer: (d) AC generator has split rings while the DC generator has a commutator.
In simple words: The main difference is that AC generators use slip rings to collect current, but DC generators use a split ring commutator to ensure the current always flows in one direction.

Exam Tip: Recall that the split ring (commutator) in a DC generator reverses the current direction in the external circuit every half rotation, ensuring unidirectional current.

Question 5. At the time of short circuit the current in the circuit
(a) reduces substantially
(b) does not change.
(c) increases heavily
(d) vary continuously.
Answer: (c) increases heavily.
In simple words: When a short circuit happens, the electric current in the circuit gets very big, very quickly.

Exam Tip: A short circuit occurs when current finds a path of very low resistance, leading to a sudden, large increase in current which can cause overheating and fire.

Question 6. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with green insulation is usually the live wire of electric supply.
Answer:
(a) False
(b) True
(c) True
(d) False.
In simple words: An electric motor actually turns electrical energy into motion, not the other way around. A generator does use electromagnetic induction. The magnetic field in the middle of a big circular coil is indeed straight and parallel. Green wire is typically for earthing, not the live wire.

Exam Tip: Understand the fundamental energy conversions for motors (electrical to mechanical) and generators (mechanical to electrical), and recall standard wire color codes and field line patterns.

Question 7. List two methods of producing magnetic fields.
Answer: The magnetic field can be produced by any of the following methods:
• Any magnet - bar magnet, horseshoe magnet or round magnet can be used.
• A wire carrying current produces a field around it.
• A loop or solenoid carrying current.
In simple words: You can create magnetic fields using a permanent magnet or by passing electric current through a wire, a coil, or a solenoid.

Exam Tip: Remember that both permanent magnets and moving electric charges (currents) are sources of magnetic fields. Electromagnetism is key here.

Question 8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. One end of the solenoid behaves as a magnetic north pole, while the other end acts as the south pole. The field lines inside the solenoid are in the form of parallel straight lines.
By taking a bar-magnet with known north poles near one end of the solenoid and if it shows repulsion then that end of solenoid is the north pole and the other end is the south pole. The property of magnets, where like poles push each other away and unlike poles pull each other together, is used to find the poles of the solenoid.
In simple words: A solenoid is a coil of wire that acts like a bar magnet when current flows through it. You can find its north and south poles by bringing a known bar magnet close; if it pushes away, that's the same pole.

Exam Tip: A solenoid's magnetic field resembles a bar magnet's, with parallel field lines inside, indicating a uniform field. The direction of current determines the polarity.

Question 9. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer: According to Flemings left-hand rule the force experienced by a current-carrying conductor placed in a magnetic field is largest when they both are perpendicular to each other.
In simple words: A wire carrying current in a magnetic field feels the strongest push or pull when the current's direction and the magnetic field are at right angles to each other.

Exam Tip: The force on a current-carrying conductor in a magnetic field is maximum when the current's direction is perpendicular to the magnetic field direction. This is fundamental to Fleming's Left-Hand Rule.

Question 10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer: According to Fleming's left-hand rule, the direction of the magnetic field is downwards.
In simple words: If an electron beam is shot forward and bends to your right because of a magnetic field, the field must be pointing downwards, according to Fleming's rule.

Exam Tip: When using Fleming's Left-Hand Rule, remember that electrons are negatively charged, so the direction of conventional current (which the rule uses) is opposite to the direction of electron flow.

Question 11. State Flemings left-hand rule. (CBSE 2015)
Answer: According to this rule, stretch the thumb, forefinger and middle finger of the left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field, the middle finger points in the direction of flow of current, then the thumb will show the direction of force acting on the conductor.
In simple words: Fleming's Left-Hand Rule says to hold your left thumb, first, and middle fingers straight out at right angles. If your first finger points where the magnetic field goes, and your middle finger points where the current goes, then your thumb will show the direction of the push or pull on the wire.

Exam Tip: Clearly state the orientation of the three fingers (mutually perpendicular) and the physical quantity each finger represents (Thumb: Force/Motion, Forefinger: Field, Middle finger: Current).

Question 12. Name some devices in which electric motors are used.
Answer: The electric motor is used in all such devices where electric energy is used, converted into mechanical energy to get the motion of the machine. For example, it is used in electric fans, mixer grinders, coolers, A.C., washing machines, and computers etc.
In simple words: Electric motors are used in many things that move using electricity, like fans, blenders, air conditioners, and washing machines.

Exam Tip: Focus on common household and industrial appliances that rely on rotational motion from electrical power when listing examples of electric motor applications.

Question 13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is -
1. pushed into the coil
2. withdrawn from inside the coil
3. held stationary inside the coil?
Answer:
1. If a bar magnet is pushed into the coil of insulated copper wire, the galvanometer shows deflection as current is induced in the coil.
2. When the bar magnet is withdrawn from the coil the galvanometer shows deflection again but now to the opposite side.
3. When the bar magnet is held stationary inside the coil, the galvanometer does not show any deflection, meaning no induced current.
In simple words: If you push a magnet into a coil, current appears. If you pull it out, current appears in the opposite direction. If the magnet stays still inside the coil, no current is made.

Exam Tip: Remember that induced current is produced only when there is relative motion between the magnet and the coil, changing the magnetic flux.

Question 14. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in coil B? Give reason.
Answer: If the current in coil A is changed, some current will be induced in coil B. The reason is that when the current in coil A is changed, the magnetic field around it also changes. As coil B is placed very close to coil A, the magnetic field lines around coil B also change, and this causes current to be induced in it.
In simple words: Yes, if current in coil A changes, current will be created in coil B. This is because changing current in A changes its magnetic field, and since B is near, B feels this change, making current appear in B.

Exam Tip: This phenomenon, known as mutual induction, relies on the changing magnetic field produced by one coil inducing an electromotive force (and thus current) in a nearby coil.

Question 15. State the rule to determine the direction of a
1. magnetic field produced around a straight conductor carrying current.
2. the force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and
3. current induced in a coil due to its rotation in a magnetic field.
Answer:
1. The rule used to determine the direction of the magnetic field produced around a straight conductor carrying current is the Right-hand thumb rule.
2. Fleming's left-hand rule is used to find the direction of force experienced by a current-carrying straight conductor when placed in a magnetic field, which is perpendicular to it.
3. Fleming's right-hand rule is used to determine the direction of current induced in a coil due to its rotation in a magnetic field.
In simple words: For a magnetic field around a straight wire, use the Right-hand thumb rule. To find the force on a current-carrying wire in a field, use Fleming's Left-hand rule. To find the current made by a rotating coil in a field, use Fleming's Right-hand rule.

Exam Tip: Differentiate clearly between the three rules: Right-Hand Thumb Rule for magnetic field direction from current, Fleming's Left-Hand Rule for force on a conductor, and Fleming's Right-Hand Rule for induced current direction.

Question 16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of the brushes?
Answer:
Principle: An electric generator works on the principle of electromagnetic induction. When a coil is rotated between the magnet or when the magnet is rotated in and out of the coil, current is induced in the coil, and the direction of current is given by Fleming's right-hand rule.
Working: As shown in the figure (diagram not rendered), when the axle attached to the two rings is rotated such that arm AB moves up and arm CD moves down in the magnetic field produced by the permanent magnet, the coil ABCD rotates clockwise. By Fleming's right-hand rule, the induced currents are set up in these arms and flow in the direction ABCD, which flows from B2 to B1.
After half a rotation, arm CD starts moving up and AB moves down. As the directions of the induced currents in both the arms change, current is induced in direction DCBA, which flows from B1 to B2. This reversing of current direction is repeated at each half rotation, so the coil continues to rotate in the same direction. The split ring helps in changing the direction of the current.
Brushes: Brushes are used to transmit the current induced externally from coil ABCD to the external circuit.
In simple words: An electric generator creates electricity using electromagnetic induction. When a coil spins in a magnetic field, current is made (Fleming's right-hand rule). The current direction keeps switching as the coil turns. Brushes collect this electricity from the spinning coil and send it out.

Exam Tip: When explaining a generator, clearly define its principle (electromagnetic induction), describe the continuous rotation of the coil, and explain the role of brushes in connecting the induced current to the external circuit.

Question 17. When does an electric short circuit occur?
Answer: An electric short circuit occurs when the insulation of a live wire gets damaged, and this bare wire comes in contact with another bare wire, such as a neutral wire. When the live wire and neutral wire come into contact, the current flowing in the circuit rises quickly, and short-circuiting happens.
In simple words: A short circuit happens when a live electrical wire accidentally touches a neutral wire. This makes the current jump very high very fast.

Exam Tip: A short circuit is characterized by a direct path of very low resistance between live and neutral wires, causing an immediate, substantial surge in current.

Question 18. What is the function of an earth wire? Why is it necessary to earth metallic appliances? (CBS E 2011)
Answer: The earth wire is connected as a safety measure to all electrical appliances that have a metallic body, for example, microwaves, electric presses, toasters, geysers, coolers, AC, etc. The earth wire provides a low resistance conducting path for electric current. If there is any leakage of current, then the user will not get any current because the current flows down into the earth and keeps the potential of the appliance and earth the same.
In simple words: An earth wire is a safety wire for metal electrical things. It gives a safe path for any leaked electricity to go into the ground. This protects people from getting shocks and keeps the appliance safe.

Exam Tip: Emphasize that the earth wire's primary role is safety, providing a low-resistance path for fault currents to prevent electrocution by keeping the appliance's potential at zero.

Gujarat Board Class 10 Science Magnetic Effects of Electric Current Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1. What does an electric current-carrying wire behave like?
Answer: It behaves like a magnet.
In simple words: A wire with electricity flowing through it acts like a magnet.

Exam Tip: Recall Oersted's discovery: an electric current creates a magnetic field, making the wire behave like a magnet.

Question 2. Define magnetic field.
Answer: The area around a magnet where its force of attraction or repulsion can be detected is called a magnetic field.
In simple words: A magnetic field is the space around a magnet where its pushing or pulling force can be felt.

Exam Tip: A magnetic field is a region of influence, not a physical object, and is characterized by both magnitude and direction.

Question 3. Define field lines.
Answer: A field line is a path along which a hypothetical free north pole would tend to move.
In simple words: A field line shows the path a tiny pretend north pole would follow if placed in a magnetic field.

Exam Tip: Magnetic field lines are imaginary lines used to represent the direction and strength of a magnetic field; they always go from north to south outside the magnet.

Question 4. What kind of quantity is a magnetic field?
Answer: It is a vector quantity as it has both magnitude and direction.
In simple words: A magnetic field is a vector, meaning it has both a size (how strong it is) and a direction (where it points).

Exam Tip: Remember that vector quantities are those that require both magnitude and direction for their complete description.

Question 5. What is a compass needle?
Answer: A compass needle is a small bar magnet.
In simple words: A compass needle is just a tiny magnet shaped like a bar.

Exam Tip: The compass needle aligns itself with the Earth's magnetic field, acting as a small bar magnet.

Question 6. What are the properties of magnetic field lines?
Answer:
• Magnetic field lines emerge from the North pole and merge at the South Pole outside the magnet and from the South pole to the North pole inside the bar magnet.
• Magnetic field lines never intersect each other because at the point of intersection the compass needle would point in two directions which is not possible.
• The magnetic field is stronger at the poles than in the middle. The direction of the magnetic field is indicated by the arrow in the line at any point (tangent).
In simple words: Magnetic field lines start at the North pole and end at the South pole outside a magnet, but go from South to North inside it. They never cross each other. They are strongest at the poles. Arrows on the lines show the field's direction.

Exam Tip: Key properties include: forming closed loops, never intersecting, and being denser where the field is stronger (at the poles).

Question 7. On which factors do the magnetic field due to current carrying conductor depend?
Answer: The magnitude of the magnetic field produced at a given point:
• Increases as the current through wire increases.
• Decreases as the distance from the wire increases.
In simple words: The strength of the magnetic field made by a current-carrying wire depends on how much current is flowing (more current, stronger field) and how far away you are from the wire (closer, stronger field).

Exam Tip: Remember the direct relationship with current and inverse relationship with distance for the magnetic field strength around a conductor.

Question 8. Name the scientist who discovered the magnetic effects of current.
Answer: Hans Christian Oersted.
In simple words: Hans Christian Oersted found out that electric current can create magnetic effects.

Exam Tip: Associate Oersted with the discovery of electromagnetism, a foundational concept linking electricity and magnetism.

Question 9. Draw the magnetic field lines due to current through a circular loop.
Answer: Magnetic lines of force are circular near the wire but become parallel at the middle point of the coil.
In simple words: For a circular wire with current, the magnetic field lines form circles close to the wire. At the very center of the loop, these lines straighten out and run parallel to each other.

Exam Tip: Visualize the field lines as concentric circles near the wire segments, gradually straightening to parallel lines through the center of the loop, indicating a uniform field there.

Question 10. What is a solenoid?
Answer: The solenoid is a long coil of many turns of insulated copper wire wrapped in the shape of a cylinder.
In simple words: A solenoid is a long, tight coil made of many layers of insulated copper wire, shaped like a cylinder.

Exam Tip: A solenoid is essentially a spring-like coil; when current passes through it, it produces a magnetic field similar to a bar magnet.

Question 11. How is solenoid different from a coil?
Answer: The solenoid is different from a circular coil in the sense that the length of the solenoid is much greater than its diameter.
In simple words: A solenoid is like a very long coil where its length is much bigger than its width, unlike a simple circular coil which is typically flatter.

Exam Tip: The key distinction is the aspect ratio: a solenoid is elongated, while a circular coil is relatively flat, affecting the uniformity and shape of their respective magnetic fields.

Question 12. What is similar between solenoid and bar magnet?
Answer: A solenoid is similar to the bar magnet.
In simple words: A solenoid acts very much like a bar magnet when electricity flows through it.

Exam Tip: Both a current-carrying solenoid and a bar magnet produce similar magnetic field patterns, with distinct North and South poles.

Question 13. What is an electromagnet?
Answer: A magnet formed temporarily due to the magnetic field of current is called an electromagnet.
In simple words: An electromagnet is a temporary magnet created when electric current flows, and it loses its magnetism when the current stops.

Exam Tip: Electromagnets are "temporary" because their magnetic properties are controlled by the presence or absence of electric current, unlike permanent magnets.

Question 14. Name and state rule used to determine the force on a current-carrying conductor in a magnetic field.
Answer: The force on a current-carrying conductor, which is placed perpendicular to the direction of the magnetic field, is given by Fleming's Left Hand Rule. According to this rule, stretch the thumb, fore-finger, and the middle finger of the left hand such that they are mutually perpendicular. If the fore-finger points in the direction of magnetic fields and the middle finger in the direction of the current, then the thumb will point in the direction of motion or force acting on the conductor.
In simple words: To find the force on a current-carrying wire in a magnetic field, use Fleming's Left Hand Rule. Point your left forefinger with the magnetic field, your middle finger with the current, and your thumb will show the direction of the force.

Exam Tip: Clearly remember that Fleming's Left-Hand Rule is for the *force* on a current-carrying conductor in a magnetic field, not for induced current or magnetic field direction.

Question 15. On what factor does strength of the magnetic field of a solenoid depend?
Answer: The strength of the magnetic field of a solenoid is proportional to the number of turns of coil and magnitude of the current.
In simple words: The magnetic field strength of a solenoid gets stronger if you add more turns of wire or send more current through it.

Exam Tip: The magnetic field strength of a solenoid increases with both the number of turns per unit length and the current flowing through it.

Question 16. Name some devices that use current-carrying conductors and magnetic field.
Answer: Electric motor, electric generator, loudspeaker and measuring instruments.
In simple words: Devices that use both electric currents and magnetic fields include electric motors, generators, speakers, and various measuring tools.

Exam Tip: Think about applications where electrical energy is converted to mechanical motion (motor) or vice-versa (generator), and where sound is produced (loudspeaker).

Question 17. How is magnetism helpful in medicine?
Answer: When we touch something, our nerves carry an electric impulse to the muscles we need to use; this impulse produces a temporary magnetic field. The magnetic field inside the body forms the basis of obtaining images of different body parts. This is done by using a technique called Magnetic Resonance Imaging (MRI). Analysis of these images helps in diagnosis and treatment.
In simple words: Magnetism helps in medicine because our body's nerve signals create tiny magnetic fields. Doctors use a special method called MRI, which uses strong magnetic fields, to take detailed pictures inside the body for finding and treating illnesses.

Exam Tip: The main medical application of magnetism is Magnetic Resonance Imaging (MRI), which uses strong magnetic fields to create detailed images of internal body structures for diagnostic purposes.

Question 18. Name two organs in the human body where the magnetic field produced is significant.
Answer: Two organs are the heart and brain.
In simple words: The heart and brain are two body parts where the magnetic fields they create are important.

Exam Tip: The electrical activity in the heart (ECG) and brain (EEG) produces weak magnetic fields, which are detectable and used in medical diagnostics like magnetoencephalography (MEG) and magnetocardiography (MCG).

Question 19. What is an electric motor? Name some devices where an electric motor is used.
Answer: An electric motor is a device which converts electric energy into mechanical energy. The devices which use electric motors are an electric fan, mixer blender, water pumps, washing machine, refrigerator etc.
In simple words: An electric motor turns electrical power into movement. It's used in things like fans, blenders, water pumps, and washing machines.

Exam Tip: An electric motor is defined by its energy conversion: electrical to mechanical. Think of common appliances that generate motion from electricity for examples.

Question 20. On what principle does electric motor work?
Answer: When the rectangular coil is placed in a magnetic field and the current passes through it, the coil experiences a torque which rotates it continuously.
In simple words: An electric motor works because a coil carrying electricity, placed in a magnetic field, feels a twisting force that makes it spin non-stop.

Exam Tip: The principle of an electric motor is based on the force experienced by a current-carrying conductor in a magnetic field, resulting in a torque that causes rotation.

Question 21. With the help of a diagram explain the working of an electric motor.
Answer:
Principle: A current-carrying conductor, when placed at a right angle to a magnetic field, experiences a force due to which it gets motion. The direction of the force is given by Fleming's left-hand rule.
Working: Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. The current flows from arm A to B and then C to D; the direction of flow of current in both arms is opposite. As per Fleming's left-hand rule, the force acting on arm AB pushes it downwards while the force acting on CD pushes it upwards. Thus, the coil and the axle rotate anti-clockwise. Due to the action of the split-ring commutator at half rotation, split rings P and Q change their contacts with brushes. Now P makes contact with Y and Q with X. As a result, current begins to flow in the coil along DCBA. Now arm AB is being pushed upward and arm CD downward by the magnetic force. So the coil rotates half a turn more in the same direction. This reversing of current direction is repeated at each half rotation, and so the coil continues to rotate in the same direction. The split ring helps in changing the direction of the current.
In simple words: An electric motor uses electricity and magnetism to make things spin. When current flows through a coil in a magnetic field, it creates forces that push one side down and the other up, making the coil turn. A special "split ring" then reverses the current's direction every half turn, which keeps the coil spinning continuously in the same way.

Exam Tip: When explaining the working of an electric motor, ensure you describe how the split-ring commutator reverses current direction to maintain continuous rotation in a single direction.

Question 22. What is the role of the split ring in an electric motor?
Answer: The role of a split ring is to reverse the direction of current flowing through the coil.
In simple words: The split ring in an electric motor flips the direction of the electric current in the coil.

Exam Tip: The split ring acts as a commutator, ensuring that the torque on the coil always acts in the same rotational direction, leading to continuous motion.

Question 23. Define electromagnetic induction.
Answer: The phenomenon of inducing an electric current in a coil by changing the magnetic field around it is called electromagnetic induction.
In simple words: Electromagnetic induction is when an electric current is created in a wire coil simply by changing the magnetic field nearby.

Exam Tip: Emphasize that it's the *change* in magnetic flux (field) that induces current, not just the presence of a magnetic field.

Question 24. Who discovered that mechanical motion can produce current?
Answer: Michael Faraday in 1831 discovered that mechanical motion can produce current.
In simple words: Michael Faraday was the scientist who found out that moving things can make electricity.

Exam Tip: Faraday's discovery of electromagnetic induction is a cornerstone of modern electrical engineering, leading to generators and transformers.

Question 25. What is a galvanometer?
Answer: A galvanometer is a device that can detect the presence of a current in a circuit.
In simple words: A galvanometer is a tool that can tell you if there is any electricity flowing in a circuit.

Exam Tip: A galvanometer is primarily for *detecting* current, particularly small ones, and often indicates direction, while an ammeter is for *measuring* larger currents.

Question 26. Name and state the rule used to determine the direction of the induced current.
Answer: The direction of the induced current is given by Fleming's right-hand rule. According to this rule, stretch the thumb, fore-finger, and the middle finger of the right hand such that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field, the thumb shows the direction of motion, and the middle finger points in the direction of induced current.
In simple words: To find the direction of electricity created by movement, use Fleming's Right-hand rule. Point your right forefinger with the magnetic field, your thumb with the movement, and your middle finger will show where the induced current goes.

Exam Tip: Carefully distinguish Fleming's Right-Hand Rule (for induced current) from Fleming's Left-Hand Rule (for force on a current). Both involve the mutually perpendicular arrangement of thumb, forefinger, and middle finger.

Question 27. What is an electric generator?
Answer: It is a device that converts mechanical energy into electrical energy.
In simple words: An electric generator is a machine that changes movement energy into electrical energy.

Exam Tip: The core function of a generator is energy transformation, specifically from mechanical input (like turning a turbine) to electrical output.

Question 28. Draw a labelled diagram of a generator.
Answer: Refer Ans.16 in NCERT textbook questions solved.
In simple words: (Answer refers to previous detailed explanation and diagram for a generator).

Exam Tip: Be prepared to draw and label the main components of a generator, including the armature coil, permanent magnets, slip rings/commutator, and brushes, understanding their functions.

Question 29. What is the difference between AC generator and DC generator?
Answer: An AC generator produces a current which changes its direction after equal intervals of time, and a DC generator produces a current which is unidirectional.
In simple words: An AC generator makes current that regularly switches direction, while a DC generator makes current that always flows in the same direction.

Exam Tip: The key difference lies in the type of current produced (alternating vs. direct) and the components used to achieve this (slip rings for AC, split-ring commutator for DC).

Question 30. What is an electric fuse?
Answer: An electric fuse is a safety device made of thin wire of tin or lead-tin alloy having a low melting point which breaks the circuit when current exceeds the safety limit.
In simple words: An electric fuse is a small safety device with a thin wire that melts and breaks the circuit if too much electricity flows through it, protecting other appliances.

Exam Tip: Fuses are crucial safety devices designed to protect circuits and appliances from damage due to excessive current by melting and breaking the circuit.

Question 31. Name the scientist who discovered the magnetic effects of current.
Answer: Hans Christian Oersted.
In simple words: The scientist who found that electric currents create magnetic effects was Hans Christian Oersted.

Exam Tip: Remember Oersted as the discoverer of the link between electricity and magnetism, paving the way for electromagnetism.

Question 32. Will current-carrying wire experience a force when kept parallel to the magnetic field?
Answer: No.
In simple words: No, a wire carrying current won't feel a push or pull if it's placed exactly parallel to a magnetic field.

Exam Tip: A current-carrying conductor experiences zero force when placed parallel (or anti-parallel) to the magnetic field lines.

Question 33. What kind of a motor is used in (a) a fan (b) a battery-operated toy?
Answer:
(a) AC motor
(b) DC motor
In simple words: A fan typically uses an AC motor, while a toy that runs on batteries uses a DC motor.

Exam Tip: AC motors run on alternating current (like from wall outlets), and DC motors run on direct current (like from batteries).

Question 34. If a current-carrying solenoid is suspended freely, how will it come at rest?
Answer: In the north-south direction like a bar magnet.
In simple words: If you hang a solenoid with current flowing through it, it will eventually stop spinning and point towards the Earth's north and south, just like a compass or a normal magnet.

Exam Tip: A current-carrying solenoid acts as a bar magnet, and a freely suspended bar magnet always aligns itself with the Earth's magnetic field in the north-south direction.

Question 35. Distinguish between permanent magnet and electromagnet.
Answer:
Permanent magnet:
• Polarity cannot be changed
• Strength remains constant
Electromagnet:
• Polarity can be changed by reversing current flow.
• Strength can be changed by varying the magnitude of the current.
In simple words: A permanent magnet always has the same strength and poles. An electromagnet, however, can have its strength and North/South poles changed by controlling the electricity flowing through it.

Exam Tip: The key differentiators are control: electromagnets offer variable strength and reversible polarity, while permanent magnets do not.

Question 36. Distinguish between DC and AC.
Answer:
DC:
• Unidirectional flow of current.
• Cells and batteries produce DC.
AC:
• Current changes its direction in a cycle.
• Dynamo produces AC.
In simple words: DC (Direct Current) flows only in one direction, like from a battery. AC (Alternating Current) constantly changes its direction, like the electricity from a power plant or dynamo.

Exam Tip: The fundamental distinction between DC and AC lies in the direction of current flow: constant for DC, periodically reversing for AC.

AC-

• Unidirectional flow of current.
• Cells and batteries produce DC.

AC:

• Current changes its direction in a cycle.
• Dynamo produces AC.

Question 37. What are the two most commonly used domestic circuit?
Answer:

• 5 A for low power rating appliances.
• 15 A for high power rating appliances.

Exam Tip: Understanding the purpose of different current ratings helps ensure electrical safety in homes.

Question 38. What is an earth wire? Why is it necessary to earth metallic appliances? (CBS E 2011)
Answer: An earth wire links to the metal casing of appliances. It offers a low resistance path for electricity, ensuring any leakage current goes safely to the earth, which lessens the risk of electric shock.
In simple words: An earth wire links to the metal casing of appliances, providing a safe path for leakage current to the earth, which then lessens the risk of electric shock.

Exam Tip: Earth wiring acts as a vital safety feature, protecting users from potential electric hazards if an appliance malfunctions.

Short Answer Type Questions

Question 1. State Fleming's left-hand rule.
Answer: Fleming's left-hand rule says to hold your thumb, forefinger, and middle finger of your left hand at right angles to each other. If the forefinger shows the magnetic field direction and the middle finger shows the current's flow, then the thumb will point to the conductor's movement.
In simple words: Fleming's left-hand rule tells us to make an L-shape with three fingers. Forefinger points to magnetic field, middle finger to current, and thumb shows the direction of force or motion.

Exam Tip: Remember that Fleming's left-hand rule is used for motors to find the direction of force, while the right-hand rule is for generators to find the induced current.

Question 2. Why do we use the power supply of two different current ratings at our homes?
Answer: At home, we use two separate circuits with different current ratings (15 A for high-power devices and 5 A for low-power ones like bulbs and fans) to prevent overloading and short-circuiting. Proper electrical fuses are installed in front of each circuit as a safety measure.
In simple words: We use two different power supplies at home (5A and 15A) to stop too many things from being plugged into one circuit and causing problems, keeping things safe.

Exam Tip: Differentiating circuits by current rating is crucial for managing power load and ensuring the safety of electrical installations and appliances.

Question 3. Give four features of domestic electric wiring.
Answer:

• All circuits are connected in parallel.
• Every circuit includes an on-off switch.
• Two distinct circuits are employed: one for 15 A and another for 5 A.
• Each circuit has an electric fuse linked to it.

Exam Tip: Parallel circuits allow appliances to operate independently, while fuses and separate circuits are essential safety mechanisms.

Question 4. Give two differences between the electric motor and generator.
Answer:
Electric Motor:

• It operates on Fleming's left-hand rule.
• It uses electric current and a magnetic field to generate movement.

Electric Generator:

• It operates on Fleming's right-hand rule.
• It uses motion and a magnetic field to create an electric current.

Exam Tip: Motors convert electrical energy into mechanical energy, while generators convert mechanical energy into electrical energy, each based on a specific Fleming's rule.

Question 5. In what ways can the magnitude of the induced current be increased?
Answer: The strength of the induced current can be increased in these ways:

• By increasing the number of turns in the wire coil.
• By using a stronger magnet.

Exam Tip: The magnitude of induced current is directly proportional to both the number of coil turns and the strength of the magnetic field.

Question 7. Give two serious hazards of electricity.
Answer: Two significant electrical hazards are:

• Fatal injury from electric shock.
• Fires caused by short-circuiting or overloading.

Exam Tip: Always handle electrical appliances with care and ensure proper wiring to prevent these life-threatening dangers.

Question 8.
(a) What would be the frequency of an alternating current if its direction changes after every 0.01 second?
(b) Which out of the two requires thin fuse wire - to draw 5 A or 15 A of current?
Answer:
(a) If an alternating current changes its direction every 0.01 seconds, the time for one complete cycle is \( 0.01 \times 2 = 0.02 \) seconds. Thus, its frequency would be \( \frac{1}{0.02} = 50 \) Hz.
(b) A thinner fuse wire is required for the 5 A circuit, as it handles a lower current.
In simple words: For part (a), if the current changes direction every 0.01 seconds, it means it takes 0.02 seconds for one full cycle, so the frequency is 50 Hz. For part (b), the 5 A circuit needs a thinner fuse wire because it carries less current.

Exam Tip: Frequency is the reciprocal of the time period for one complete cycle. Thinner fuse wires are designed for lower current ratings to melt and break the circuit faster, providing protection.

Question 9. Draw a schematic diagram of domestic wiring system and write its main features.
Answer:

(Note: The diagram from the source PDF is not directly convertible to SVG with all details, so a placeholder image tag is used to indicate its position and a descriptive caption is provided below.)
**Main Features of Domestic Wiring System:**

• Circuits are always connected in parallel.
• Each circuit includes a Miniature Circuit Breaker (MCB), which serves as a small, individual fuse.
• There are two distinct circuits: one for 5 A and another for 15 A.
• The earth wire is always linked to the metal casing of appliances.

Exam Tip: A well-designed domestic wiring system ensures safety and efficiency by using parallel circuits, protective devices like MCBs and fuses, and proper earthing.

Question 10. Name the components of electric motor that is used for the application of Fleming's left-hand rule.
Answer: In an electric motor, the key components applying Fleming's left-hand rule include:
* **A coil with many turns:** A large number of wire turns amplifies the magnetic force, producing a very powerful force.
* **Electromagnet:** The strength of the electromagnet can be adjusted by raising the current, which then increases the motor's motion.
* **Soft iron core:** A soft iron core inside the motor helps boost its overall power output.
In simple words: An electric motor uses a coil with many turns, an electromagnet whose strength can be changed, and a soft iron core. These parts help create a strong force based on Fleming's left-hand rule, making the motor move.

Exam Tip: The interaction between the magnetic field, current, and the coil's structure creates the mechanical force in a motor, as described by Fleming's left-hand rule.

Question 11. Give three important features of the magnetic field due to current carrying solenoid coil.
Answer: The magnetic field generated by a current-carrying solenoid coil has these important characteristics:
* Inside the solenoid, the magnetic field lines are almost straight and parallel to each other.
* The solenoid acts like a bar magnet because its magnetic field lines are very strong at its ends (poles).
* It also exhibits the directional and attractive qualities typically found in a magnet.
In simple words: For a solenoid, the magnetic field lines inside are straight and parallel. It acts like a bar magnet, with strong field lines at the poles, and also shows direction and attraction.

Exam Tip: Remember that the magnetic field inside a solenoid is uniform, making it useful for creating strong, controlled magnetic fields.

Question 12. Draw magnetic field through and around a solenoid carrying electric current.
Answer:

The image shows a coiled loop of wire, which forms a solenoid. The S and N indicate the South and North poles. The lines represent the magnetic field.
In simple words: The diagram displays a coiled wire (solenoid) with its magnetic field lines. The lines inside are straight, while outside, they loop from the North pole to the South pole.

Exam Tip: When drawing magnetic field lines for a solenoid, remember they are parallel and uniform inside, resembling a bar magnet's field lines outside.

Question 13. Name the factors on which force produced due to magnetic field depends
Answer: The force created by a magnetic field is influenced by several factors:
* The length of the conductor.
* The amount of electric current flowing through it.
* The strength of the magnetic field itself.
* The direction of the current and the magnetic field; the greatest force happens when they are at right angles to each other.
In simple words: The strength of the force from a magnetic field depends on the conductor's length, the current's strength, the magnetic field's power, and if the current and field are at a 90-degree angle, the force will be strongest.

Exam Tip: The force experienced by a current-carrying conductor in a magnetic field is maximized when the current direction is perpendicular to the magnetic field direction.

Question 14.
(a) Distinguish between the terms overloading and short-circuiting as used in domestic circuits.
(b) Why are the coils of electric toasters made of an alloy rather than a pure metal?
Answer:
(a) **Overloading** happens when too many appliances are connected to one power outlet, attempting to draw more current than the circuit can safely provide. **Short-circuiting** occurs when a large current flows due to appliance malfunction or when the live and neutral wires directly touch each other.
(b) Electric toaster coils are made from alloys, not pure metals, because alloys have a higher electrical resistance and do not easily oxidize or burn at the high temperatures needed for toasting.
In simple words: For (a), overloading means too many devices drawing power, while short-circuiting means a huge current flow due to a fault. For (b), toaster coils are made of alloys because they resist electricity more and do not easily burn at high heat.

Exam Tip: Both overloading and short-circuiting are dangerous situations that can lead to fires or damage to electrical systems, hence the importance of protective measures. Alloys are preferred for heating elements due to their specific electrical and thermal properties.

Question 15. When is the force experienced by a current-carrying conductor placed in a magnetic field the largest?
Answer: The force experienced by a current-carrying conductor in a magnetic field is greatest when the conductor's length (which indicates current direction) and the magnetic field (B) are perpendicular to each other. In this case, the maximum force is calculated as \( F = IB \).
In simple words: The biggest force on a current-carrying wire in a magnetic field happens when the current's path and the magnetic field are at right angles. The formula for this force is \( F = IB \).

Exam Tip: This principle is fundamental to how electric motors work, where the goal is to maximize the force for rotation.

Question 16.
(a) What is the standard colour code followed for
1. Live
2. Neutral
3. Earth
wires used in electric circuits?
(b) Which part of an electric appliance is earthed and why?
Answer:
(a) The standard color code for wires in electrical circuits is:
1. **Live wire:** Red
2. **Neutral wire:** Blue
3. **Earth wire:** Green
(b) The metallic casing or body of an electric appliance is earthed. This is done to provide a safe path for any leakage current to flow directly into the ground, preventing electric shocks to the user.
In simple words: For (a), live wires are red, neutral wires are blue, and earth wires are green. For (b), the metal part of an appliance is earthed so that if electricity leaks, it goes safely into the ground, protecting people from shocks.

Exam Tip: Proper color coding is essential for safe electrical wiring, and earthing metallic appliance bodies is a critical safety measure to protect against electric shocks.

Question 17. In a power plug why is the one point longer as shown in the figure than the other two?
Answer: In a power plug, the longest pin at the top is the earth pin. This design ensures that when an electrical appliance with a metal body is plugged in, the earth connection is established first. This safety feature helps protect a person from electric shocks by channeling any fault current safely to the ground.
In simple words: The longest pin on a power plug is the earth pin. It's longer to connect first, so if there's an electrical fault, the current goes to the ground safely, preventing shocks.

Exam Tip: The earth pin's length ensures that the appliance's metal casing is grounded before power is supplied, offering crucial protection against electrical faults.

Question 18. Name the materials used to make an electromagnet. Explain how you can make one in
Answer: To create an electromagnet, you can use steel or iron as the core material. In a laboratory setting, you would need a power source (like a battery), insulated metal wire, and safety gloves. First, form a loop with the wire. Then, similar to a solenoid, wrap the insulated wire around a soft steel or iron core. Connect the ends of this coil to the battery terminals. Once current flows through the wire, the core inside becomes magnetized and can attract other magnetic materials.
In simple words: To make an electromagnet, use an iron or steel core. Wrap insulated wire around it, connect to a battery, and current makes it magnetic. It attracts things while the current is on.

Exam Tip: Electromagnets are temporary magnets whose strength and polarity can be controlled by varying the current, making them highly versatile in various applications.

Question 19. Name the magnetic materials.
Answer: The common magnetic materials include iron, nickel, and cobalt.
In simple words: Iron, nickel, and cobalt are examples of magnetic materials.

Exam Tip: These materials are called ferromagnetic because they can be strongly magnetized.

Question 20. Suggest two ways of increasing the strength of the magnetic field lines produced by a circular coil carrying current.
Answer: Here are two methods to increase the magnetic field strength produced by a current-carrying circular coil:
(a) Increase the amount of current passing through the coil.
(b) Increase the number of turns or coils in the wire.
In simple words: To make a coil's magnetic field stronger, you can either put more electricity through it or use more loops of wire.

Exam Tip: The magnetic field strength is directly proportional to both the current and the number of turns in the coil.

Question 21. State the difference in the electromagnet and permanent magnet
Answer: Here are the key differences between an electromagnet and a permanent magnet:
Electromagnet:

• It is a temporary magnet.
• It can be easily demagnetized.
• Its magnetic strength can be adjusted.
• Its polarity can be reversed, and it is usually made from soft iron.

Permanent Magnet:

• It is a permanent magnet.
• It cannot be easily demagnetized.
• Its magnetic strength remains fixed and cannot be changed.

Exam Tip: Electromagnets offer control over their magnetic properties, making them suitable for applications requiring adjustable magnetic fields, unlike permanent magnets which have fixed properties.

Long Answer Type Questions

Question 1.
(a) What is meant by a magnetic field?
(b) How is the direction of the magnetic field at a point determined?
(c) Describe an activity to demonstrate the direction of the magnetic field generated around a current-carrying conductor.
(d) What is the direction of the magnetic field at the centre of a current-carrying circular loop?
Answer:
(a) A **magnetic field** is the area surrounding a magnet or a current-carrying conductor where its magnetic force can be detected.
(b) The direction of the magnetic field at any specific point is determined using a compass needle, which aligns itself with the field lines.
(c) **Activity to demonstrate the direction of the magnetic field around a current-carrying conductor:**
Take a thick copper wire and insert it through the center of a cardboard sheet, keeping the wire vertical. Connect the wire to a battery and a key. Place a compass on the cardboard near the wire. When current flows through the wire (by closing the key), the compass needle deflects, indicating a magnetic field. By moving the compass around the wire, you can see that the needle aligns itself in concentric circles, with the direction of deflection changing as you move. Reversing the current direction will reverse the compass deflection. This demonstrates that a magnetic field is produced around the conductor, and its direction can be found using the right-hand thumb rule.
(d) At the center of a current-carrying circular loop, the magnetic field lines are straight and perpendicular to the plane of the loop.
In simple words: For (a), a magnetic field is the area around a magnet or current where its force is felt. For (b), a compass needle shows the magnetic field's direction. For (c), an activity with a wire, cardboard, and compass shows that current creates a circular magnetic field around the wire, and its direction is found using the right-hand thumb rule. For (d), the magnetic field at the center of a circular current loop is straight.

Exam Tip: Understanding the concept of a magnetic field and its direction is crucial for analyzing the behavior of magnets and current-carrying conductors. The right-hand thumb rule is key for determining the field's direction.

Question 2.
(a) What is an electromagnet? What does it consist of?
(b) Name one material in each case which is used to make a
(i) Permanent magnet
(ii) Temporary magnet
(c) Describe an activity to show how can you make an electromagnet in your school laboratory.
Answer:
(a) An **electromagnet** is a type of magnet where the magnetic field is produced by an electric current. It is a temporary magnet, meaning it loses its magnetism once the current is switched off. It typically consists of insulated wire wound around a core of soft magnetic material.
(b)
(i) **Permanent magnet:** Alloys like alnico (an alloy of aluminum, nickel, and cobalt).
(ii) **Temporary magnet:** Soft iron.
(c) **Activity to make an electromagnet in the laboratory:**
Gather materials such as a solenoid, a soft iron core, a battery, and a key. Insert the soft iron core inside the solenoid. Connect the ends of the solenoid's wire to the battery through the key. When you close the key, current will flow through the solenoid, and the soft iron core inside will become magnetized, thus forming an electromagnet. You can then demonstrate its magnetic properties, which will disappear once the current is switched off.
In simple words: For (a), an electromagnet is a temporary magnet made by passing electricity through a wire coil around a soft magnetic core. For (b), alnico is for permanent magnets, and soft iron is for temporary ones. For (c), you can make an electromagnet by putting a soft iron core inside a wire coil (solenoid) and connecting it to a battery with a key; when the current flows, it becomes magnetic.

Exam Tip: Electromagnets are valuable for applications where magnetic strength needs to be controlled, such as in cranes, doorbells, and circuit breakers.

Question 3. Describe an activity to show that a magnetic field is produced by an electric current flowing through a circular coil of wire.
Answer:
**Aim:** To demonstrate that an electric current flowing through a circular coil of wire generates a magnetic field.
**Apparatus Required:** Iron filings, a circular coil with a known number of turns, a cardboard sheet, a stand, an electric key, a battery, and a rheostat.
**Procedure:**
* Mount the circular coil through two holes in the cardboard sheet, secured by a stand.
* Connect the open ends of the coil to a battery using a key and a rheostat.
* Position the coil vertically, ensuring the cardboard lies horizontally.
* Sprinkle iron filings evenly over the cardboard.
* Close the key to allow current to flow and gently tap the cardboard. Observe how the iron filings arrange themselves.
* Use a compass needle to find and mark the direction of the magnetic field.
* Reverse the current direction in the coil and note any changes in the compass needle's orientation.
**Observations:**
The iron filings on the cardboard arrange themselves to show the magnetic field lines. These lines are observed to be:
* Circular in shape near the wire segments.
* Straight and parallel at the coil's center.
* Perpendicular to the plane of the coil.
* Uniform in larger areas, particularly at the center of the field.
**Conclusion:** The formation of a circular pattern of iron filings around the wire and straight lines at the center confirms the generation of a magnetic field by the current-carrying circular coil.
In simple words: To show current in a circular coil creates a magnetic field, set up a coil through cardboard, sprinkle iron filings, and connect to a battery. When current flows and you tap, the filings form patterns (circles near wire, straight at center) that show the magnetic field. A compass can then confirm its direction.

Exam Tip: This activity clearly illustrates the magnetic effect of current in a circular loop and helps visualize the magnetic field pattern, which is concentrated and uniform at the center.