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

Very Short Answer Type Questions :

Question. What is the pattern of field lines inside a solenoid? What do they indicate? 
Answer: The magnetic field is in the form of parallel lines. It indicates a uniform magnetic field because magnetic field lines are parallel.

Question. How is magnetic field produced in a solenoid used? 
Answer: It is used to magnetise a soft iron bar to form an electromagnet.

Question.Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer: The direction of magnetic field will be perpendicular to the plane of paper inwards inside the loop and perpendicular to the plane of paper outwards from inside.

Question. What type of core is used to make electromagnets? 
                                          OR
What type of core should be put inside a current-carrying solenoid to make an electromagnet?
Answer: Soft Iron

Question. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Answer: The force experienced by a current carrying conductor placed in a magnetic field is largest when the conductor is placed with its length in a direction perpendicular to that of magnetic field.

Question. Why don’t two magnetic lines of force intersect each other?
Answer: No, two magnetic field lines can ever intersect each other. If they do, then it would mean that at the point of intersection there are two directions of magnetic field, which is not possible. 

Question. State the observation made by Oersted on the basis of his experiment with current carrying conductors.
Answer: A magnetic field is produced near a current carrying conductor which last so long till there is current in the conductor on reversing the current the direction of magnetic field is also reversed.

Question. Give the factors on which magnetic field produced by a current carrying solenoid will depend.
Answer: (i) The current through the solenoid. (ii) The number of turns in the solenoid
(iii) Nature of core on which wires are wound in solenoid.

Question. (a) Electric fuse is an important component of all domestic circuits. Why?
(b) An electric oven of rating 2 kW, 220 V is operated in a domestic circuit with a current rating of 5 A. What result would you expect? Explain.
Answer: Electric fuse is a safety device which has high resistance and low melting point and prevents electric appliances during short circuiting and overloading. By melting itself, a fuse break the circuit.

Question. Name the factors on which force acting on a current carrying conductor will depend.
Answer: (i) The current through the conductor. (ii) The strength of magnetic field.
(iii) The length of the conductor.

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, when a current in coil A changes, magnetic field lines linked with coil B also change. Hence, due to change in number of magnetic field lines, there is an induced current in coil B

Question. What does the thumb indicated in Fleming’s right hand rule?
Answer: Thumb indicate the direction of force on conductor i.e. motion of the conductor.

Question. How is the magnetic field produced in a solenoid used?
Answer: Magnetic field produced in a solenoid can be used in making a soft iron piece electromagnet.

Question. Mention the special feature regarding shape of magnetic field lines.
Answer: Magnetic field lines are continuous closed loops.

Short Answer Type Questions :

Question. Identify the type of magnetic fields represented by the magnetic field fines given below and name the type conductors which can produce them.

Answer: 

Question. What happens to the deflection of the compass needle placed at a point near current carrying straight conductor:
a. if the current is increased?
b. if the direction of current in the conductor is changed (reversed)?
c. if compass is moved away from the conductor?
Answer: a. If the current increases deflection of compass increases.
b. If the direction of current is reversed the deflection in the compass needle is also reversed.
c. Deflection of the compass needle decreases when compass is moved away from the conductor.

Question. Differentiate overloading and short- circuiting.
Answer: Overloading means to draw current more than the permitted maximum current in the circuit which may be due to connecting many appliances in one socket.
In short circuiting, when live wire and neutral wire come in contact with each other then resistance of the circuit becomes minimum consequently the current in the circuit increases abruptly. It may be due to damage of insulation of wire.

Question. Write one difference between direct current and alternating current. Which one of the two is mostly produced at power stations in our country? Name one device which provides alternating current. State one important advantage of using alternating current.
Answer: Direct current has constant magnitude and unidirectional current. Alternating current changes its magnitude and direction alternatively.
a. Alternating current is produced in power stations in India.
b. AG generators are used to produce AC.
c. AC voltage can be increased or decrease with the help of a transformers.

Question. An alpha particle (positively charged) enters a magnetic field at right angle to it as shown in figure. Explain with the help of relevant rule,the direction of force acting on the alpha particle. 

Answer: The force will act in upward direction given by thumb, if forefinger points in the direction of magnetic field and the middle finger points in the direction of current, according to Fleming’s left hand rule.

Question. (i) A compass needle gets deflected when brought near a current carrying conductor. Why?
(ii) What happens to the deflection of needle when current in the conductor is increased? 
Answer: (i) It is because current carrying conductor produces a magnetic field which superimposes with magnetic field of compass needle due to which needle of compass gets deflected.
(ii) The deflection in the magnetic needle will increase as the strength of current increases.

Question. Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors which can produce them.

Answer: (a) These magnetic field lines are produced by a current carrying loop.
(b) These are magnetic field lines produced by solenoid.

Question. What is meant of solenoid? How does a current carrying solenoid behave? Give its main use.
Answer: The long coil containing large number of close turns of insulated copper wires wrapped around, is called a solenoid.
Current carrying solenoid behaves like a bar magnet. It is called an electromagnet.
It is used for making electromagnets.

Question. State Fleming’s left-hand rule.
Answer: Fleming’s left hand rule states that stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field and central finger that of the current, then the thumb will point towards the direction of motion of the conductor.

Question. List three methods of producing magnetic field.
Answer: Three methods of producing magnetic fields are as follows:
(a) Magnetic field can be produced by placing a permanent magnet or a horse-shoe magnet at the place, where magnetic field is required.
(b) Magnetic field is produced around a current carrying straight conductor or a current carrying coil.
(c) A very good method to produce magnetic field is due to flow of current in a solenoid.

Question. What is the principle of an electric motor?
Answer: An electric motor is based on the principle that the current carrying conductor experiences a force when placed in a magnetic field. If the direction of the magnetic field and that of the current are mutually perpendicular, then the direction of the force is given by Fleming’s left-hand rule.

Question. What is the principle of electric motor? State the function of (i) split ring (ii) field magnet used in electric motor.
Answer: Electric motor works on the principle that a current carrying conductor placed perpendicular to a magnetic field experiences a force.
(i) Split ring – It reverses the dissection of current in the armature and thus direction of force is also reserved. As a result dc motor continues to rotate in same direction.
(ii) Field magnet – It provided strong magnetic field.

Question. State the rule to determine the direction of a (i) magnetic field produced around a straight current carrying conductor
(ii) force experienced by a current carrying straight conductor
(iii) current induced in a coil due to its rotation in a magnetic field.
Answer: (i) To know the direction of magnetic field produced around a straight conductor we make use “Right hand thumb Rule”.
(ii) To find the direction of force experienced by a current carrying straight conductor placed in a magnetic field we make use “Fleming’s left hand rule”.
(iii) For finding the direction of current induced in a coil we use “Fleming’s right hand rule”.

Question. Find the minimum rating of fuse that can be safely used on a line on which two 1.1 kW, electric geysers are to run simultaneously. The supply voltage is 220 V.
Answer: I = Total Power/V = nP /V
= 2 X 1.1kW/220V
= 2 X 1.1 X 1000 /220V W = 10 A
So a fuse wire of rating must be greater than 10 A.

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: No, current carrying solenoid behaves like a bar magnet and will stay only geographical N and S direction. If the direction of current is reversed then the polarity of the magnet will change and hence will rotate through an angle of 180°.

Question. What is meant by electromagnetic induction? State the rule which helps in determining direction of induced current.
Answer: Electromagnetic induction is the phenomenon of production of emf (potential difference) or current in a coil due to change in magnetic field around it.
Fleming right hand rule: If we stretch our right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, and thumb points the direction of force acting on the conductor (motion of the conductor), then the middle finger points the direction of induced current in the conductor.

Question. State three factor on which magnetic field produced by a current carrying solenoid depends.
Answer: (1) The strength of the current flowing through the solenoid.
(2) No. of turns of the wire of the solenoid.
(3) Nature of the material inside solenoid.

Question. How does a solenoid behave like a magnet? Can you determines the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.
Answer: When current is passed through a solenoid coil, magnetic field is produced due to presence of turns in same direction. As a result, the resultant magnetic field is very strong and uniform.
Solenoid behaves like a strong bar magnet. We can determine the poles of magnet formed by solenoid. The end of solenoid connected with positive terminal behaves like South Pole and the end connected with negative terminal behaves as North Pole.

Question. The magnetic field associated with a current-carrying straight conductor is in anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current.
Answer: Direction of current – east to west as determined by Right-hand thumb rule. Ri’-lu-Uand Thumb Rule: If we hold a current-carrying conductor by right hand in such a way that the stretched thumb is along the direction of current, then the curly fingers around the conductor represents the direction of field lines of magnetic field.

Question. How is the strength of magnetic field near a straight current-conductor (i) related to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer: (i) The strength of magnetic field around a straight current conductor increases on increasing the strength of current in the conductor or vice versa.
(ii) The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Question. Imagine that you are sitting in chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer: An electron beam moving horizontally from back wall towards the front wall is equivalent to a current flowing in the opposite direction. The deflection of electron beam as seen by the observer is to his right side. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.

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. Explain different ways to induce current in a coil.
Answer: Different ways to induce current in a coil are as follows:
(a) If a magnetic field is changed around a coil then an induced current is set up in the coil.
(b) If a coil is moved in magnetic field, then again an induced current is set up in the coil.
(c) If a coil is rotated in a uniform magnetic field

Question. If we place a compass needle near straight conductor carrying current (a) What happens to the deflection of the compass needle if the direction of current reversed. Is
(b) What change will you notice in the compass needle if it is moved away from conductor but the current through the conductor remains the same?
Answer: (a) Direction of deflection will reverse
(b) Deflection will decrease

Question. Two coils A and B of insulated wires are kept close to each other. Coil A is connected to a galvanometer while coil B is connected to a battery through a key. What would happen if (i) a current is passed through coil B by plugging the key, and (ii) the current is stopped by removing the plug from the key?
Explain your answer mentioning the name of the phenomenon involved.
Answer: In both the given cases, galvanometer shows momentary deflection but in opposite direction. In coil A, magnetic field lines [increased in case (i) and decreased in case (ii)] induce a potential difference across the coil A which sets up induced electric current in coil A. It is shown by the deflection in galvanometer. This is known as electromagnetic induction.

Question.What are magnetic field lines? Justify the following statements
(a) Two magnetic field lines never intersect each other.
(b) Magnetic field lines are closed curves.
Answer: Magnetic field lines: It is defined as the path along which the unit North pole (imaginary) tends to move in a magnetic field if free to do so.
(a) The magnetic lines of force do not intersect (or cross) one another. If they do so then at the point of intersection, two tangents can be drawn at that point which indicates that there will be two different directions of the same magnetic which field, i.e. the compass needle points in two different directions which is not possible.
(b) Magnetic field lines are closed continuous curves. They diverge from the north pole of a bar magnet and converge its south pole. Inside the magnet they move from south pole to north pole.

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. Why does a current carrying conductor kept in a magnetic field experience force? On what factors does the direction of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Around a current carrying conductor a magnetic field is produced. When it is placed in a magnetic field then both fields interact each other, and current carrying conductor experience a force.
Fleming’s left hand rule: If we stretch right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current, then thumb will point the direction of force on the conductor.

Question. What does the direction of thumb indicate in the right hand thumb rule? In what way this rule is different from Fleming’s left hand rule?
Answer: Thumb indicate the direction of current in a straight conductor held in right hand. Fleming’s left hand rule gives the direction of force on a current carrying conductor placed in magnetic field.
Fleming’s left hand rule : If we stretch right hand thumb, forefinger and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current, then thumb will point the direction of force on the conductor.

Question. A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is
(i) moved quickly towards it,
(ii) moved quickly away from the coil and
(iii) placed near its one face?
Name the phenomenon involved.
Answer: (i) Deflection in the galvanometer needle will be more on right-side.
(ii) Larger deflection in opposite direction as compared to the case (i) will be seen. (Hi) No deflection.
The phenomenon involved is electromagnetic induction.

Question. What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer: Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid. img
When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity, i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

Long Answer Type Questions :

Question. (a) Draw the pattern of magnetic field lines through a bar-magnet and around a current carrying solenoid.
(b) What is the pattern of magnetic field lines inside the solenoid and what does these indicate?
(c) How can a solenoid be utilised to make an electromagnet? 
(d) State two ways by which the strength of this electromagnet can be increased.
Answer: 

(b) These are parallel straight lines indicating that magnetic field is uniform inside the solenoid.
(c) By inserting a soft iron rod into the middle part of solenoid it is used to make an electromagnet
(d) (i) By increasing the number of turns.
(ii) By increasing the strength of current.

Question. With the help of a labelled circuit diagram describe an activity to illustrate the pattern of the magnetic field lines around a straight current carrying long conducting wire.
(i) Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor.
(ii) Is there a similar magnetic field produced around a thin beam of moving:
(a) alpha particles and (b) neutrons? Justify your Answer:
Answer: (i) Take a battery (12 V), a variable resistor (rheostat), an Ammeter (0.5 A), a plug key, a long thick straight copper conducting wire.
(ii) Insert the thick wire through the centre normal to the plane of rectangular cardboard.
(iii) Take care that cardboard is fixed and does not slide up or down.
(iv) Connect the copper wire vertically between points X and Y as shown in diagram in series with battery, plug and a key.
(v) Sprinkle some iron flings unformly on the cardboard.
(vi) Keep the variable resistance in fixed position.
(vii) Close the key so that current flows through the wire.
(viii) Ensure the copper wires placed remains vertically straight.
(ix) Gently tap the iron filings.

Observation:
Iron filings align themselves showing a pattern of concentric circles around the copper wire which represents magnetic lines of force.
(i) Right hand rule.
(ii) (a) Yes, alpha particle being positively charged constitutes a current in the direction of motion.
(b) No, neutrons being electrically neutral constitute no current.

 Question. With the help of diagram of experimental set up describe an activity to show that the force acting on a current carrying conductor placed on magnetic field increases with increase in field strength.
Answer: (i) Take an aluminium rod, AB of size 3 inches.
(ii) Suspend it horizontally using connecting wires
(iii) Place a horse-shoe magnet in such a way that the rod lies between the two poles with magnetic field directed upwards.
(iv) Put north pole of the magnet vertically below and south pole vertically above the rod.
(v) Connect aluminium rod in series with the battery and key.
(vi) Now pass the current in the rod from B to A.
(vii) Aluminium rod will be displaced towards the left.
(viii) Now bring a stronger horse-shoe magnet and observe the displacement of rod.
(ix) The displacement of rod will increase with the increase in strength of the magnetic field.

Question. Under what condition does a current carrying conductor kept in a magnetic field experience maximum force? On what other factors does the magnitude of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Force on a current carrying conductor in a magnetic field depends upon
a. length of the conductor
b. strength of the magnetic field
c. strength of the current
d. angle between direction of magnetic field and current.
Fleming’s Left Hand Rule:
Fleming’s left hand rule gives the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it. According to Fleming’s left hand rule if we stretch our left hand thumb, forefinger and middle finger in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current then thumb will give the direction of force on the conductor.