CBSE Class 10 Science Magnetic Effects of Electric Current Assignment Set F

Very Short Answer Type Questions :

Question. State the principle of an electric generator.
Answer: An electric generator is based on the principle of electromagnetic induction. When a rectangular coil is rotated in a uniform magnetic field, an induced emf is generated between the ends of the coil.

Question. State and define S.I unit of magnetic field?
Answer: The S.I unit of magnetic field is Tesla (T). The magnetic field strength is said to be one Tesla if 1meter long conductor carrying 1 ampere current experiences 1 Newton force, when placed perpendicular to the direction of magnetic field.

Question. A beam of alpha particles enters a chamber moving along the magnetic field. What is the magnetic force experienced by the beam?
Answer: Zero, it is because beam is moving parallel to the magnetic field.

Question. A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor with the help of a magnetic compass. He reports that:
a. the degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
b. the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
Which of the above observations of the student appears to be wrong and why?
Answer: The first statement is wrong because the strength of magnetic field decreases when we move away from a current carrying conductor. So deflection in the compass, instead of increasing must decrease.

Question. What is electric fuse? Where it is connected in a circuit?
Answer: An electric fuse is a safety device which is made up of a wire made of copper or aluminum or a tin lead alloy. An electric fuse must be connected in the path of the circuit so that overloading which can cause fire due to short circuit can be avoided.

Question. sources produce alternating current?
Answer: A.C. generator and common inverter used in houses for emergency power supply produce alternating current.

Question. Write any one method to induce current in a coil.
Answer: By moving a magnet towards the coil or vice versa, current can be induced in the coil.

Question. When does an electric short circuit occurs?
Answer: If either the insulation of wires used in an electric circuit is damaged or there is a fault in the appliances, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short circuiting occurs.

Question. When is the force experienced by a current carrying conductor placed in a magnetic field greatest?
Answer: When the current in the conductor flows perpendicular (90°) to the direction of the magnetic field, maximum force is generated.

Question. Can a freely suspended current carrying solenoid stay in any direction? Justify your Answer: What will happen when the direction of current in the solenoid is reversed? Explain. 
Answer: A current carrying solenoid behaves like a bar magnet. When it is suspended freely it will stay in north–south direction. On reversing the direction current, it will turn to 180°° because its polarity will be reversed.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field forces an particle (+ve charged) be projected to that it is deflected southward? Name and state the rule you have to use to find the direction in this force. 
Answer: The direction of motion of particles is from west to east. Fleming’s left hand rule is used to find the direction of force.

Question. Mention the angle between a current carrying conductor and magnetic field for which the force experienced by this current carrying conductor placed in magnetic field is largest?
Answer: If the angle between a current carrying conductor and magnetic field is 90° then the force experienced by the conductor is maximum.

Question. Suggest one way of discriminating a wire carrying current from a wire carrying no current.
Answer: When a magnetic compass is brought near a current carrying conductor it will be deflected. If magnetic compass remains undeflected near a conductor then there is no current in it.
a. Magnetic field lines of a current carrying circular loop.
b. Magnetic field lines in a solenoid.

Question. Why are magnetic field lines closed curves?
Answer: By convention the magnetic field lines are the path traced by north pole which emerges from north pole and goes to the south pole and inside the magnet the direction of field lines are from south pole to north pole, forming continuous closed path.

Question. State two ways by which the strength of an electromagnet can be increased.
Answer: By increasing the strength of current and number of turns of the solenoid we can increase the strength of an electromagnet.

Question. What does the direction of thumb indicate in the right-hand thumb rule?
Answer: Thumb points the direction of current in the conductor holding a straight conductor in right hand.

Question. What does the direction of thumb indicate in the right hand thumb rule? 
Answer: The thumb indicates the direction of current in the straight conductor held by curved fingers of our hand.

Short Answer Type Questions :

Question. You are given three identical looking bars one of which is a magnet, the other made of a magnetic material and the third made of a non magnetic material. Using just these three bars how will you find out which is which? 
Answer: Bring one bar close to the other two one by one: if the bar attracts one of these and does not attract the
other one, the bar which is not attracted is made of non-magnetic material and the bar in our hand is
a magnet or a bar of magnetic material. Keep one bar on the table and move other bar along its length
from one end to the other, if uniform attraction is felt the bar in our hand is a magnet and vice versa.

Question. Draw a labelled diagram of an electric motor. Explain its principle and working.
What is the function of split ring in an electric motor?
Answer: Electric motor labelled diagram of an electric motor is as follows:
Principle: A current-carrying conductor, when placed in a magnetic field, experiences a force. If the direction of magnetic field and that of current are mutually perpendicular then force acting on the conductor will be perpendicular to both and will be the given by Fleming’s left-hand rule. Due to this force the conductor begins to move, if it is free to rotate. Working: Let the current in the coil ABCD of motor enters from the source battery through the conducting brush X, flow along ABCD and finally flows back to the battery through brush Y. On applying Fleming’s left-hand rule we find that force acting on arm AB due to magnetic field pushes it downwards. But the force acting on arm CD pushes it upwards. Thus, the coil and the axle rotate anticlockwise. Due to action of 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 coil along DCBA. The arms are pushed in opposite direction and coil continues to rotate in same direction.

Question. Explain the principle, construction and working of an electric motor with a help of labeled diagram?
Answer: Principle – it is based on the principal that a current carrying conductor placed perpendicular to the magnetic field experiences a force.
Construction-
(i) Armature or coil- It consist of an insulated copper wire wound on a soft iron core.
(ii) Strong field magnet- two pole pieces of a strong magnet provides a strong magnetic field.
(iii) Split ring- it consist of two halves(R1 and R2) of a metallic ring which reverses the direction of the current in a coil.
(iv) Brushes- two carbon brushes touch the commutator (split ring).
(v) Battery – a battery is connected across the carbon brushes.

Question. Why does a current carrying conductor kept in a magnetic field experience force?
What is the direction of force acting on the conductor?
Answer: A current carrying coil contains charged particles which experiences a force (Bqv). The total force experienced by the charged particle is equal to the force experienced by the conductor which is perpendicular to both the magnetic field and the direction of current in the conductor.

Question. Why and when does a current carrying conductor kept in magnetic field experiences force? List the factors on which direction of force will depend. 
Answer: The movement of electrons takes place in the conductor in a particular direction when current is passed through it. These charged particles are moving in the magnetic field which experiences force.The current carrying conductor has its own magnetic field, when it superimpose the magnetic field of magnet. Due to this, current carrying conducter experiences a force. Thus conductor experiences a force when placed in a uniform magnetic field.
Factors on which direction of force depends:
(i) The direction of force depends upon the direction of magnetic field.
(ii) It also depends upon the direction of current flowing through the conductor.

Question. How is the strength of magnetic field near a straight current-carrying conductor
(i) related to the strength of current in the conductor?
(ii) is affected when the direction of flow of current is reversed?
Answer: (i) The strength of magnetic field is directly proportional to the strength of current.
(ii) If we reverse the direction of current, the direction of magnetic field will also be reversed.

Question. (a) Explain what is the difference between direct current and alternating current? Write one important advantage of using alternating current.
(b) An air conditioner of 2 kW is used in an electric circuit having a fuse of 10 A rating. If the potential difference of the supply is 220 V, will the fuse be able to withstand, when the air conditioner is switched on? Justify your answer.
Answer: (a) Direct current is a unidirectional current with constant magnitude. Alternating current is a current which change its magnitude and direction after a fixed period. AC voltage can be increased or decreased. Where is dc voltage cannot be increased or decreased. AC can be transmitted to long distances with lesser power loss.
(b) Given P = 2 kW and V = 200 volt, 
Power, P = VI ⇒ I = p/v
I = 2000/220 = 9.09 A
The rating of the fuse wire is 10 A which is greater than current drawn by air conditioner so when air conditioner is switched on, fuse will not blow off

Question. For the circular coil carrying current shown alongside, draw magnetic field lines. Decide which of its face behaves as North Pole and which face as South Pole.
Give reason to justify your answer.

Answer: From the front face magnetic field emerges out of the coil and enters out from the back face so front face will behave as north pole and back face as south pole.

Question. Name any three factors on which the magnitude of the magnetic field due to solenoid depends.
Answer: Factors on which the magnitude of the magnetic field due to solenoids
a. number of turns in the solenoid
b. area of cross section of the coil
c. strength of current in solenoid

Question. Draw the pattern of field lines due to a solenoid carrying electric current. Mark the north and south poles in the diagram.
Answer: The pattern of the magnetic field lines is as shown in figure.

Question. What is the function of an earth wire? Why is if necessary to earth metallic casing of electric appliance?
Answer: Earth will acts as a safety device. When live wire touches the metallic appliance then electric current flows through castling to the earth instead of human body and thus we prevent ourselves from getting shock. It is necessary to earth metallic casing of the appliance because it saved electrical appliance from burning and prevent us from electric shock.

Question. (a) What is short circuiting?
(b) What is overloading? How can you avoid overloading?
Answer: (a) Short circuiting means when live wire and the neutral wires come in contact with each other. Due to this resistance of the circuit becomes very small and huge amount of current flows through the circuit which is turn produces more heat which can cause fire.
(b) Overloading means large amount of current flows in the circuit. It can happen when many electrical appliances of high power ratings are connected in a single socket. It can be avoided by the following methods:
(i) Not use too many appliance is a single socket
(ii) To apply preventive methods of short circuiting.

Question. Define electromagnetic induction? 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 the coil B? Explain.
Answer: Electromagnetic induction means the production of induced current in a closed coil due to the change in the magnetic field. When current in coil A is changed, magnetic flux sets up around coil A due to which some magnetic field set up in the coil B thus some induced current flow through coil B due to which galvanometer deflects.

Question. (a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Answer: 

Question. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The earth wires functions as a safety measure, especially for those appliances that have a metallic body, like heater, electric, press, room cooler etc. The metallic body of the appliance is connected to the earth wire, which provides a low resistance conducting path for electric current. It ensures that any leakage of current to the metallic body of an appliance keeps it potential same as of earth. As a result, the user would not get severe electric shock, even if he touches the body of appliance.

Question. A magnet is moving towards a coil as shown in figure.

(1) Which phenomenon is shown in figure.
(2) Which physical quantity is between magnet and coil? set up in the coil when there is a relative motion
(3) What may be the cause of production of that physical quantity?
Answer: (1) Electromagnetic induction
(2) Induced current
(3) Change in magnetic lines of forces through coil

Question. A student while studying the force experienced by a current carrying conductor in a magnetic field records the following observations:
a. The force experienced by the conductor increases as the current is increased.
b. The force experienced by the conductor decreases as the strength of the magnetic field is increased.
Which of the two observations is correct and why?
Answer: First observation is correct because when current increases force also increase. From equation of force on a current carrying conductor F = BIl.F α I i.e. more current more force on a current carrying conductor in a magnetic field.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field should an a-particle (which are positively charged particles) be projected so that it is deflected south ward? Name and state the rule you have used to find the direction in this case.
Answer: Forefinger – direction of magnetic field (upwards).
Thumb – direction of force (southwards) Middle finger gives direction of current or direction of positively charged particle (East) i.e. from west to east a particles must be projected.

Question. Write one application for each of the following:
(a) Right-hand Thumb Rule,
(b) Fleming’s left Hand Rule,
(c) Fleming’s Right Hand Rule.
Answer: (a) It is used to find the direction of magnetic field in a coil of wire and electric current in a straight conductor.
(b) It is used to find the direction of force exerted on a current carrying conductor in a magnetic field.
(c) It is used to find the direction of induced current in a closed circuit placed in a changing magnetic field, e.g. in an electric generator.

Question. What is short circuiting? State one factor/condition that can lead to it. Name a device in the household that acts as a safety measure for it. State the principle of its working.
Answer: Short circuiting: When electric circuit offers very low resistance to the flow of current through it, the current increases heavily and the circuit is said to be short circuited. It occurs when live wire touches the neutral wire. This happens due to the damage in insulation of the power lines.
Safety measure device: Fuse.
Working principle of fuse: It works on the heating effect of electric current or Joule’s law of heating.
According to this law, the heat produced in a resistor is directly proportional to the (i) square of current for a given resistance.
(ii) resistance for a given current and (iii) time for which the current flows through the resistor.
H = I2Rt
So, when current in the circuit increases, the wire with low melting point in it melts to the heat generated.
Hence, the circuit breaks and electrical devices and appliances are saved.

Question. Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer: (a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.

Question. State one main difference between A.C. and D.C. Why is A.C. preferred over D.C. for long range transmission of electric power? Name one source each of D.C. and A.C.
Answer: Difference between A.C. and D.C.: The alternating current (A.C.) reverses its direction periodically whereas the direct current (D.C.) always flows in one direction.
A.C. is preferred over D.C. because it can be transmitted over long distance without much loss of energy.
D.C. source: Battery A.C. source: A.C. generator

Question. How will the magnetic field produced at a point due to a current carrying circular coil change if we:
(i) increase the current flowing through the coil, (ii) reverse direction of current through coil,
(iii) increase the number of turns in the coil? 
Answer: (i) The strength of magnetic field will increase. ( B ∝ I)
(ii) The direction of magnetic field will be reversed.
(iii) The magnetic field produced will increase because magnetic field produced is directly proportional to the number of turns in the coil.

Question. 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 the coil B? Give reason.
Answer: Yes, a current is induced in the coil B.
When the current in the coil A is changed, the magnetic field associated with it also changes.
As coil B is placed close to A, hence magnetic field lines around this coil also change. Due to change in magnetic field lines associated with coil B, an induced current is also induced in it.

Question. An electron enters a magnetic field at right angles to it as shown in fig. The direction of the force acting on the electron will be:
(a) to the right (b) to the left (c) out of the page (d) into the page
Answer: When a conductor carrying current is placed perpendicular to the direction of magnetic field, the acting on it is given by Fleming’s left hand rule. Since the direction of current is the same as that of the motion of a positive charge, the direction of force acting on it when moving perpendicular to the direction of magnetic field is the same as that acting on a current-carrying conductor placed perpendicular to the direction of magnetic field.
Obviously, the force acting on an electron is opposite to that. Therefore, in this case it is into the page.

Question. (a) Two magnets are lying side by side as show.
Draw magnetic field line between poles P and Q.
(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer: 

(b) The degree of closeness of magnetic field lines near the poles signify that the field is stronger there, i.e. the pole of another magnet when placed in the magnetic field experiences a greater force where the field lines are crowded.

Question. For the current carrying solenoid as shown below, draw magnetic field lines and giving reason explain that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum.

Answer: Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half to that inside it. So Minimum – at point B; Maximum – at point A

Long Answer Type Questions :

Question. Describe an activity to show magnetic field lines are produced when current is passed through circular coil.

Answer: (i) Take a rectangular cardboard having two holes.
(ii) Insert a circular coil through these holes, normal to the plane of paper.
(iii) Connect the ends of coil in series with a battery, and key.
(iv) Sprinkle iron filings uniformly on the cardboard.
(v) Plug the key.
(vi) Tap the cardboard gently a few times. Note the pattern of the iron filings.
(vii) The pattern of magnetic field lines will be same as the pattern of iron filings.

Question. With the help of a diagram of experimental setup describe an activity to show that the force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.
Answer: Aim : To show that force acting on a current carrying conductor placed in a magnetic field increases with the field strength.
Apparatus Required : Aluminium rod, stand horse shoe magnet of different intensity, cell, key and connecting wires.
Procedure :
1. .Arrange the set-up as shown in figure.

2.Plug the key, the current flowing through the rod from Q to P observe the displacement of rod.
3.Now unplug the key and remove the first horse shoe magnet and place the second horse shoe magnet of higher magnetic field strength in a similar manner to that of first.
4.Plug the key, the current again flow through the rod from Q to P. Again observe the deflection of rod.
5.Now bring both’the magnet closer together (to ensure greater magnetic field than that of previous case). Again observe the motion of rod.
Observations : Each time, the conductor moves faster than that of previous one. It is possible only when conductor gets accelerated more each time which required more force. (F = ma) Thus, if the magnetic field strength is increased, the rod will experience a greater force and move faster.
Conclusion : The force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.