Class 10 Science · Chapter 12

Magnetic Effects of Electric Current

279 Class 10 Science questions on Magnetic Effects of Electric Current from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

NCERT exercises

Exercises (9) Intext Questions (Page 196) (1) Intext Questions (Page 200) (3) Intext Questions (Page 201) (3) Intext Questions (Page 203) (3) Intext Questions (Page 205) (3)

NCERT Exemplar exercises

Multiple Choice Questions (12) Short Answer Questions (12) Long Answer Questions (8)

CBSE Class 10 Science previous year papers, with answers →

Questions · page 12 of 14

Q221 CBSE 2022
In the diagram given below, Coil – 1 is connected in series with a battery and a plug key while Coil – 2 is connected with a galvanometer.
1. (i)Why does the galvanometer show deflection only when the key (K) is plugged in and not when a steady current starts flowing in the circuit ?
2. (ii)What is observed in the galvanometer, when the key is plugged out ?
3. (iii)State the conclusion based on the observation of this activity.
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G deflects only while the current in coil-1 is changing, and oppositely on plugging out; a changing field induces a current.
(i) When the key is plugged in, the current in coil-1 grows from zero to its steady value, so the magnetic field it produces, and with it the magnetic field lines linked with coil-2, change. This change induces a potential difference and a momentary current in coil-2, so the galvanometer deflects. Once the current becomes steady, the magnetic field no longer changes, no current is induced, and the needle comes back to zero. (ii) When the key is plugged out, the current in coil-1 falls to zero and the field lines linked with coil-2 decrease. The galvanometer needle again deflects momentarily, but to the opposite side, because the induced current now flows in the opposite direction. (iii) A potential difference, and hence a current, is induced in a coil whenever the magnetic field linked with it changes; here the changing current in coil-1 induces a current in coil-2. This is electromagnetic induction.

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Q222 CBSE 2022
In the figure given below, a simple electric motor is shown : As shown in the figure, the current in the coil ABCD flows from A to B in the arm AB and C to D in the arm CD.
1. (i)State the directions in which the arms AB and CD will experience a force.
2. (ii)Identify the part of the electric motor that reverses the flow of current in the coil ABCD and write its name.
3. (iii)After the reversal of flow of current in the coil ABCD, state the directions in which the arms AB and CD will experience a force.
4. (iv)Name the rule which is applied to determine the direction of force on a current carrying conductor placed in a magnetic field.
Show answer

AB is forced down and CD up; the split-ring commutator reverses the current; the forces then reverse; Fleming's left-hand rule.
(i) The arm AB experiences a force vertically downwards and the arm CD a force vertically upwards, so the coil turns (anticlockwise as seen from the front). (ii) The split ring, the two half rings P and Q, reverses the current in the coil; it acts as a commutator (split-ring commutator). (iii) After the reversal, the arm AB experiences a force upwards and the arm CD a force downwards, so the coil keeps turning in the same direction. (iv) Fleming's left-hand rule.

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Q223 CBSE 2022
1. (i)What is a magnetic needle ? Why does a magnetic needle get deflected when brought near a current carrying straight conductor ?
2. (ii)State right hand thumb rule.
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A magnetic needle is a small pivoted bar magnet; it deflects because the current's magnetic field exerts forces on its poles.
(i) A magnetic needle is a small, light, thin bar magnet pivoted at its centre so that it can turn freely; left to itself it points roughly north–south, and it is the needle of a magnetic compass. Near a current-carrying straight conductor it is deflected because the current produces a magnetic field around the conductor, whose field lines are concentric circles around the wire. The poles of the needle experience forces in this field, so the needle turns away from north–south towards the direction of the field lines at its position. (ii) Right-hand thumb rule: imagine holding the current-carrying straight conductor in your right hand so that the thumb points in the direction of the current; then the fingers wrapped around the conductor point in the direction of the field lines of the magnetic field.

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Q224 CBSE 2022
1. (i)The magnetic field in a region is represented by equidistant parallel lines. What do such lines indicate ?
2. (ii)Imagine that you are sitting in an examination room 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 ?
3. (iii)State the rule which you have applied in determining the direction of the magnetic field in this case.
Show answer

Equidistant parallel lines show a uniform field; the field is vertically downward, found by Fleming's left-hand rule.
(i) Equidistant parallel field lines indicate a uniform magnetic field: the field has the same strength and the same direction at every point of the region, as inside a long current-carrying solenoid. (ii) The magnetic field is vertically downward. The electrons move from the back wall to the front wall, so the conventional current is from the front wall towards the back wall; with the current towards the back wall and the force to your right, Fleming’s left-hand rule gives a field pointing vertically downward. (iii) Fleming’s left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force on the conductor, that is, its direction of motion.

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Q225 CBSE 2022
AB is a coil of copper wire having a large number of turns. The ends of the coil are connected with a galvanometer as shown. When the north pole of a strong bar magnet is moved towards the end B of the coil, a deflection is observed in the galvanometer.
1. (a)State the reason for using galvanometer in the activity and why does its needle deflects momentarily when magnet is moved towards the coil.
2. (b)What would be observed in the galvanometer in a situation when the coil and the bar magnet both move with the same speed in the same direction ? Justify your answer.
3. (c)(i)State the conclusion that can be drawn from this activity. Will there be any change in the momentary deflection in the galvanometer if number of turns in the coil is increased and a more stronger magnet is moved towards the coil ?
4. (c)(ii)OR : What is electromagnetic induction ? What is observed in the galvanometer when a strong bar magnet is held stationary near one end of a coil of large number of turns ? Justify your answer.
Show answer

Current is induced only while the linked field changes: no deflection when coil and magnet move together or the magnet is stationary.
(a) A galvanometer is an instrument that detects the presence of a current in a circuit and shows its direction; the current induced in the coil is small and lasts only a moment, so a galvanometer, whose pointer rests at the central zero and deflects to either side, is used to detect it. Its needle deflects only momentarily because a current is induced in the coil only while the magnetic field linked with the coil is changing, that is, while the magnet is moving towards the coil; the moment the magnet stops, the field stops changing, the induced current falls to zero and the needle returns to zero. (b) No deflection is observed. When the coil and the magnet move with the same speed in the same direction there is no relative motion between them, so the magnetic field linked with the coil does not change and no current is induced. (c)(i) Conclusion: the motion of a magnet with respect to a coil (a change in the magnetic field linked with the coil) induces a potential difference in the coil, which sets up an induced current in the circuit; this is electromagnetic induction. Yes, the momentary deflection becomes larger: with more turns and a stronger magnet the change in the magnetic field linked with the coil is greater, so a larger current is induced. OR (c)(ii) Electromagnetic induction is the process by which a changing magnetic field in a conductor induces a current in another conductor; a current is induced in a coil whenever the magnetic field linked with it changes. When a strong bar magnet is held stationary near one end of the coil the galvanometer shows no deflection, because the magnetic field linked with the coil is not changing, so no current is induced, however strong the magnet or however many the turns.

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Q226 CBSE 2022
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.
1. (a)Draw a diagram to show this pattern of iron filings.[1]
2. (b)What does this pattern of iron filings demonstrate ?[1]
3. (c)(i)How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ?[2]
4. (c)(ii)OR : How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.[2]
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(a) The diagram shows the bar magnet at the centre, with its N and S ends, and the iron filings lying end to end along curves that leave one end of the magnet, loop round and reach the other end. The curves are crowded near the two ends (the poles) and spread out farther away, and none of them crosses another (see the figure). (b) It demonstrates the magnetic field around the magnet: the magnet exerts a force on the filings in the region around it, and the lines along which the filings align themselves represent the magnetic field lines. The filings crowd near the poles, where the field is strongest. (c)(i) The direction of the magnetic field at a point is given by the tangent to the field line at that point, in the sense of the arrow on the line - the direction in which the north pole of a compass needle placed there points. Two field lines never cross, because at a crossing there would be two tangents, that is, two directions of the field at one point, and a compass needle placed there would have to point in two directions at once, which is not possible. OR (c)(ii) Fix a sheet of white paper on a drawing board, place the magnet on it and mark its boundary. Place a small compass near the north pole and mark both ends of the needle. Move the compass so that the south end of the needle sits where its north end was, and mark the north end again. Continue step by step until the compass reaches the south pole, and join the marks by a smooth curve: that is one field line. The drawing shows one such line above the magnet and one below it, each leaving the N pole and entering the S pole, with arrows from N towards S (see the figure).

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Q227 CBSE 2022
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.
1. (a)Draw a diagram to show this pattern of iron filings.[1]
2. (b)What makes iron filings arrange in a definite pattern ?[1]
3. (c)(i)How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ?[2]
4. (c)(ii)OR : How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.[2]
Show answer

(a) The iron filings line up along curves that start at one pole of the magnet, bend round its sides and end at the other pole, on both sides of the magnet; they are crowded near the two poles and more widely spaced farther away (see the figure). (b) The magnetic field of the bar magnet. In this field the iron filings experience a force that differs from point to point in magnitude and direction; each filing is magnetised and turns, like a tiny compass needle, to lie along the field where it is, so the filings arrange themselves along the magnetic field lines. Tapping only frees them to turn. (c)(i) The direction of the magnetic field at a point is the direction of the tangent to the field line at that point, in the sense of the arrow on the line; it is the direction in which the north pole of a compass needle placed there points. Two field lines never cross because at the point of crossing there would be two tangents, that is, two directions of the field at one point, and a compass needle there would have to point in two directions at once, which is not possible. OR (c)(ii) Place the magnet on a sheet of white paper fixed on a drawing board and mark its outline. Put a small compass near the N pole, mark the positions of both ends of its needle, then move the compass so that its south end lies on the mark of its north end and mark the new north end. Repeat step by step until the S pole is reached, and join the marks with a smooth curve: that is a field line, with its arrow in the direction in which the needle's north end pointed. One such line on each side of the magnet runs from the N pole round to the S pole, with the arrows from N to S outside the magnet (see the figure).

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Q228 CBSE 2022
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions :
1. (a)Why does the rod get displaced on passing current through it ?
2. (b)State the rule that determines the direction of the force on the conductor AB.
3. (c)(i)(i) In the above experimented set up, when current is passed through the rod, it gets displaced towards the left. What will happen to the displacement if the polarity of the magnet and the direction of current both are reversed ? (ii) Name any two devices that use current carrying conductors and magnetic field.
4. (c)(ii)OR : Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically on a horizontal cardboard. Indicate the direction of the field lines as well as the direction of current flowing through the conductor.
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(a) The rod carries a current and lies in the magnetic field of the horseshoe magnet. A current-carrying conductor placed in a magnetic field experiences a force (the field of the current interacts with the field of the magnet), and this force, acting at right angles to both the rod and the field, pushes the rod sideways. (b) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, the thumb points in the direction of the force, that is, of the motion of the conductor. (c)(i) (i) The rod is still displaced towards the left. Reversing the polarity of the magnet alone would reverse the force, and reversing the current alone would reverse it too; reversing both reverses it twice, so its direction is unchanged (and, with the same current and magnet, so is its size). (ii) The electric motor and the loudspeaker (others: the electric generator, the microphone, and measuring instruments such as the galvanometer). OR (c)(ii) The field lines are concentric circles on the cardboard, centred on the conductor and spaced wider apart farther from it. With the current flowing upward through the conductor they run anticlockwise as seen from above (right-hand thumb rule); with a downward current they run clockwise.

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Q229 CBSE 2022
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions :
1. (a)State the condition under which the displacement of the rod is largest for the same magnitude of current flowing through it.
2. (b)State the rule that determines the direction of the force on the conductor AB.
3. (c)(i)(i) If the U shaped magnet is held vertically and the aluminum rod is suspended horizontally with its end B towards due north, then on passing current through the rod from B to A as shown, in which direction will the rod be displaced ? (ii) Name any two devices that use current carrying conductors and magnetic field.
4. (c)(ii)OR : Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically on a horizontal cardboard. Indicate the direction of the field lines as well as the direction of current flowing through the conductor.
Show answer

(a) The displacement is largest when the rod, that is the direction of the current, is at right angles to the direction of the magnetic field. (b) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular; if the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, the thumb points in the direction of the force on (motion of) the conductor AB. (c)(i) (i) The field is vertically upward (N pole below the rod, S pole above) and the current flows from north to south, so by Fleming's left-hand rule the rod is displaced towards the west. (ii) Electric motor and loudspeaker (the electric generator, the microphone and the galvanometer are other examples). OR (c)(ii) The field lines are concentric circles on the cardboard, centred on the wire and closer together near it; for a current flowing upward they run anticlockwise as seen from above (right-hand thumb rule), and clockwise if the current flows downward (see the figure).

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Q230 CBSE 2022
AB is a coil of copper wire having a large number of turns. The ends of the coil are connected with a galvanometer as shown. When the north pole of a strong bar magnet is moved towards the end B of the coil, a deflection is observed in the galvanometer.
1. (a)State the reason for using galvanometer in the activity and why does its needle deflects momentarily when magnet is moved towards the coil.
2. (b)A deflection in the galvanometer is also observed when the magnet is held stationary and the coil is moved towards the south of pole of the magnet. Why ?
3. (c)(i)State the conclusion that can be drawn from this activity. Will there be any change in the momentary deflection in the galvanometer if number of turns in the coil is increased and a more stronger magnet is moved towards the coil ?
4. (c)(ii)OR : What is electromagnetic induction ? What is observed in the galvanometer when a strong bar magnet is held stationary near one end of a coil of large number of turns ? Justify your answer.
Show answer

(a) A galvanometer detects the presence of a current in a circuit and shows its direction, its pointer deflecting to the left or right of the centre zero; the induced current is usually small and brief, so this sensitive detector is used. While the magnet moves towards the coil, the magnetic field linked with the coil changes, which induces a potential difference and a current in the coil, so the needle deflects. When the motion stops, the field stops changing, the induced current stops and the needle returns to zero, so the deflection is momentary. (b) Because there is still relative motion between the coil and the magnet: as the coil moves towards the south pole, the magnetic field linked with the coil changes, so a current is induced in it and the galvanometer deflects. It does not matter whether the magnet or the coil moves. (c)(i) Conclusion: relative motion between a magnet and a coil, which changes the magnetic field linked with the coil, induces a potential difference and an electric current in the coil (electromagnetic induction); the current flows only while the field is changing. Yes, the momentary deflection increases: more turns and a stronger magnet both increase the induced potential difference, and so the induced current, for the same motion. OR (c)(ii) Electromagnetic induction is the production of a potential difference, and hence a current, in a conductor such as a coil when the magnetic field linked with it changes. When a strong bar magnet is held stationary near one end of the coil, the galvanometer shows no deflection: the field through the coil is not changing, so no current is induced, however strong the magnet.

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Q231 CBSE 2022
AB is a coil of copper wire having a large number of turns. The ends of the coil are connected with a galvanometer as shown. When the north pole of a strong bar magnet is moved towards the end B of the coil, a deflection is observed in the galvanometer.
1. (a)What is a galvanometer ? Why does its needle deflects when magnet is moved towards the coil to which it is connected ?
2. (b)What would be observed in the galvanometer in a situation when the coil and the bar magnet both move with the same speed in the same direction ? Justify your answer.
3. (c)(i)State the conclusion that can be drawn from this activity. Will there be any change in the momentary deflection in the galvanometer if number of turns in the coil is increased and a more stronger magnet is moved towards the coil ?
4. (c)(ii)OR : What is electromagnetic induction ? What is observed in the galvanometer when a strong bar magnet is held stationary near one end of a coil of large number of turns ? Justify your answer.
Show answer

(a) A galvanometer is an instrument that detects the presence of a current in a circuit; its pointer stays at zero (the centre of the scale) when no current flows and deflects to the left or right of zero depending on the direction of the current. As the magnet moves towards the coil, the magnetic field through the coil changes; this changing field induces a potential difference across the coil, which sets up an induced current through the galvanometer, so its needle deflects, only while the magnet is moving. (b) No deflection is observed: the needle stays at zero. The coil and the magnet move together, so there is no relative motion between them; the magnetic field through the coil does not change, so no current is induced. (c)(i) Conclusion: a changing magnetic field, produced here by moving the magnet relative to the coil, induces a current in the coil (electromagnetic induction), and the current lasts only while the field keeps changing. Yes, the momentary deflection increases: with more turns and a stronger magnet moved in the same way, a larger current is induced, so the needle deflects further. OR (c)(ii) Electromagnetic induction is the process by which a changing magnetic field induces a current in a conductor. With a strong bar magnet held stationary near one end of the coil, the galvanometer shows no deflection, because the magnetic field through the coil, though present, is not changing, so no current is induced.

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Q232 CBSE 2022
Take two different coils of copper wire having large number of turns, say 50 and 100 turns respectively. Insert them over a non-conducting roll as shown in the given figure. Connect the Coil-1, having large number of turns, in series with a battery and a plug key. Also connect the other Coil-2 with a galvanometer.
Figure for (c)(ii)
1. (a)Name the two coils used in the given activity.
2. (b)Define the phenomenon involved in this case.
3. (c)(i)Explain the reason for the current which is responsible for the deflection in the galvanometer.
4. (c)(ii)OR : A coil AB of copper wire is connected to a galvanometer as shown in the figure. What is observed when N-pole of a strong bar magnet is (I) pushed into the coil, and (II) held stationary inside the coil ? State the reason for each observation.
Show answer

(a) Coil-1, connected to the battery and the key, is the primary coil; Coil-2, connected to the galvanometer, is the secondary coil. (b) Electromagnetic induction: the process by which a changing magnetic field in a conductor induces a current in another conductor. (A potential difference is induced in a coil whenever the magnetic field linked with it changes.) (c)(i) On closing (or opening) the key, the current in coil-1 rises (or falls), so the magnetic field it produces, and hence the magnetic field lines linked with coil-2, change. This change induces a potential difference and a current in coil-2, which deflects the galvanometer for a moment. When the current in coil-1 becomes steady, the field stops changing, and the induced current and the deflection fall to zero. OR (c)(ii) (I) When the N-pole is pushed into the coil, the galvanometer needle deflects momentarily, because the moving magnet changes the magnetic field linked with the coil and a current is induced in it. (II) When the magnet is held stationary inside the coil, there is no deflection, because the magnetic field linked with the coil does not change and no current is induced.

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Q233 CBSE 2022
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.
1. (a)Draw a diagram to show this pattern of iron filings.[1]
2. (b)Draw the magnetic field lines of a bar magnet showing the poles of the bar magnet as well as the direction of the magnetic field lines.[1]
3. (c)(i)How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ?[2]
4. (c)(ii)OR : How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.[2]
Show answer

Iron filings crowd at the poles and arch from one pole to the other; field lines leave N and enter S and never cross.
(a) The iron filings arrange themselves along curved lines: they crowd thickly near the two ends of the magnet, its poles, and run in curves from one pole round the magnet to the other, thinning out further away (drawn in the figure). (b) The magnet is marked N and S. The field lines come out of the north pole, curve round outside the magnet and go into the south pole, with arrows pointing from N to S outside the magnet; inside the magnet they run from S to N, so each line is a closed loop. The lines are closest together near the poles, where the field is strongest, and no two lines cross (drawn in the figure). (c)(i) The direction of the magnetic field at a point is the direction of the tangent to the field line at that point, in the sense of the arrow on the line — the direction in which the north pole of a compass needle placed there points. Two field lines do not cross because at the point of crossing there would be two tangents, and so two directions of the field at one point; a compass needle placed there would have to point in two directions at once, which is not possible. OR (c)(ii) Fix a sheet of white paper on a drawing board, place the bar magnet at its centre and mark its outline. Place a small compass near the north pole of the magnet and mark the positions of the two ends of its needle with dots. Move the compass so that its south end is at the dot where its north end was, and mark the new position of the north end. Repeat until the compass reaches the south pole. Join the dots with a smooth curve and mark its direction by the way the north end of the needle pointed: this is one field line. Starting once on each side of the magnet gives one field line on each side (drawn in the figure).

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Q234 CBSE 2022
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions :
1. (a)Why does the rod get displaced on passing current through it ?
2. (b)State the rule that determines the direction of the force on the conductor AB.
3. (c)(i)(i) If the U shaped magnet is held vertically and the aluminum rod is suspended horizontally with its end B towards due north, then on passing current through the rod from B to A as shown, in which direction will the rod be displaced ? (ii) Name any two devices that use current carrying conductors and magnetic field.
4. (c)(ii)OR : Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically on a horizontal cardboard. Indicate the direction of the field lines as well as the direction of current flowing through the conductor.
Show answer

The magnet exerts a force on the current-carrying rod; Fleming's left-hand rule gives its direction; here the rod moves west.
(a) The current in the rod produces a magnetic field around it, which interacts with the field of the horse-shoe magnet; the magnet therefore exerts a force on the current-carrying rod, perpendicular to both the rod and the field, and the freely suspended rod is displaced. Reversing the current reverses the force, so the displacement reverses. (b) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular; if the forefinger points along the magnetic field and the middle finger along the current, the thumb points in the direction of the force (motion) on the conductor. (c)(i) (i) The field between the poles points vertically upwards (N pole below, S pole above) and the current flows from B (north) to A, that is towards the south. By Fleming's left-hand rule the force, and so the displacement of the rod, is towards the west. (ii) Any two of: electric motor, electric generator, loudspeaker, microphone, measuring instruments such as the galvanometer. OR (c)(ii) The field lines are concentric circles on the cardboard, centred on the conductor and closer together near it. With the current flowing upwards through the cardboard, the right-hand thumb rule makes the circles run anticlockwise when viewed from above (clockwise if the current flows downwards), as drawn in the figure.

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Q235 CBSE 2022
Take two different coils of copper wire having large number of turns, say 50 and 100 turns respectively. Insert them over a non-conducting roll as shown in the given figure. Connect the Coil-1, having large number of turns, in series with a battery and a plug key. Also connect the other Coil-2 with a galvanometer.
Figure for (c)(ii)
1. (a)State what is observed in the galvanometer, when (i) the key is closed. (ii) the key is opened.
2. (b)Define the phenomenon involved in this case.
3. (c)(i)Explain the reason for the current which is responsible for the deflection in the galvanometer.
4. (c)(ii)OR : A coil AB of copper wire is connected to a galvanometer as shown in the figure. What is observed when N-pole of a strong bar magnet is (I) pushed into the coil, and (II) held stationary inside the coil ? State the reason for each observation.
Show answer

Closing and opening the key deflect the needle momentarily in opposite directions: electromagnetic induction; OR only a moving magnet deflects it.
(a) (i) When the key is closed, the galvanometer needle deflects momentarily to one side and returns to zero. (ii) When the key is opened, the needle deflects momentarily to the opposite side and returns to zero. (b) Electromagnetic induction: the process by which a changing magnetic field in a conductor induces a current in another conductor. (c)(i) Closing the key makes the current in coil-1, and so its magnetic field, grow from zero. That field passes through coil-2, so the magnetic field linked with coil-2 changes, and this change induces a potential difference and a current in coil-2, which deflects the galvanometer. When the current becomes steady the field stops changing and the induced current stops; opening the key makes the field fall, which induces a current in the opposite direction. OR (c)(ii) (I) When the N-pole is pushed into the coil, the galvanometer needle deflects while the magnet moves, because the magnetic field through the coil changes and induces a current in it. (II) When the magnet is held stationary inside the coil, there is no deflection, because the field through the coil is not changing, so no current is induced.

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Q236 CBSE 2022
A student wants to demonstrate a phenomenon of science in a science fair. He takes a straight solenoid fixed vertically on a wooden board and connects its two ends to a galvanometer. He also takes a strong bar magnet whose south pole is attached to a spring and suspends it with its axis vertical using a wooden stand in such a way that the north pole of the magnet is slightly above the upper end of the solenoid. He also ensures the free in and out movement of the north pole in the stationary solenoid. Now he pushes the magnet slightly downward and then releases it. The magnet starts oscillating. Based on your understanding, answer the following questions :
1. (a)What is observed in the galvanometer when the magnet oscillates and why ?[1]
2. (b)What is observed in the galvanometer when the amplitude of oscillation is decreased to about one-half and why ?[1]
3. (c)(i)State the type of movement shown by the needle of the galvanometer. What may be the reason for such a motion ? Write the conclusion which can be drawn from this activity.[2]
4. (c)(ii)OR : Name and define the phenomenon demonstrated through this activity. Name the scientist who discovered this phenomenon.[2]
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The oscillating magnet induces an alternating current, so the needle swings to both sides, less for a smaller amplitude: electromagnetic induction (Faraday).
(a) The galvanometer needle is deflected first to one side and then to the other, repeatedly, as long as the magnet oscillates. The north pole moving into and out of the solenoid keeps changing the magnetic field linked with the solenoid, and this changing field induces a current in it; the current flows one way while the pole moves in and the opposite way while it moves out. (b) The needle still swings to both sides, but through a smaller angle. With a smaller swing on the same spring the magnet moves more slowly, so the magnetic field linked with the solenoid changes less, and less rapidly, and the induced current is smaller (for small swings, roughly half). (c)(i) The needle shows an oscillatory, to-and-fro movement about its zero mark. The reason is that the induced current reverses its direction every time the magnet reverses its direction of motion. Conclusion: a changing magnetic field linked with a coil, produced here by relative motion between a magnet and the coil, induces an electric current in the coil, and the direction of the current depends on the direction of the motion; a magnet moving to and fro therefore induces an alternating current. OR (c)(ii) The phenomenon is electromagnetic induction: the production of an induced potential difference, and so of an electric current, in a coil when the magnetic field linked with it changes, for example when a magnet is moved into or out of the coil. It was discovered by Michael Faraday.

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Q237 CBSE 2020

The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.

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The phenomenon is electromagnetic induction: a changing magnetic field through a coil induces a current in it.
Electromagnetic induction: a change in the magnetic field lines through a coil induces a current, the induced current, in it.

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Q238 CBSE 2020

State an important advantage of using alternating current (a.c.) over direct current (d.c.).

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Alternating current can carry electric power over long distances without much loss of energy.
An important advantage of a.c. over d.c. is that electric power can be transmitted over long distances without much loss of energy.

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Q239 CBSE 2020

Define the term induced electric current.

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Induced current is the current produced in a closed conductor when the magnetic field around it changes.
Induced electric current is the current produced in a conductor (a closed coil or circuit) when the magnetic field around it changes, for example when a magnet is moved towards or away from a coil. The process is called electromagnetic induction.

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Q240 CBSE 2020
Fleming’s Right-hand rule gives
1. (a)magnitude of the induced current.
2. (b)magnitude of the magnetic field.
3. (c)direction of the induced current.
4. (d)both, direction and magnitude of the induced current.
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(c) direction of the induced current.

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