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.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 6 of 14

1. Q101 CBSE 2025
   Two statements ​are given below ​— one labelled as Assertion (A) and the other ​labelled as Reason (R). Select the correct ​answer ​to this question from the codes (a), (b), (c) and (d) given below.

   Assertion (A): Magnetic field lines around a bar magnet never intersect each other.

   Reason (R): Magnetic field produced by a bar magnet is a quantity that has both magnitude and direction.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

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2. Q102 CBSE 2025
   Two statements are ​given ​below — one labelled ​as Assertion (A) and the other labelled as Reason (R). Select the correct answer ​to this question ​from the codes (a), (b), (c) and ​(d) as ​given ​below.

   Assertion (A): In our homes we receive supply of electric power through a main supply. One of the wires in this supply, usually with red insulation, is called live wire and another wire with green insulation is called neutral wire.

   Reason (R): In our country, the potential difference between the live wire and the neutral wire is 220 volts.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (d) Assertion (A) is false, but Reason (R) is true.

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3. Q103 CBSE 2025
   Question Nos. 17 to ​20 consists ​of two ​statements ​– Assertion (A) and Reason ​(R). Answer these questions selecting ​the ​appropriate option from (a), (b), (c) and (d) ​given below :

   Assertion (A): The pattern of the magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

   Reason (R): The pattern of the magnetic field around a current carrying conductor is independent of the shape of the conductor.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (c) Assertion (A) is true, but Reason (R) is false.

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4. Q104 CBSE 2025
   Two statements are given below – one labelled as Assertion (A) and ​the ​other ​labelled as Reason (R). Select the correct ​answer to this question from the codes (a), (b), (c) ​and (d) ​given ​below.

   Assertion (A): In the common domestic circuits the earth wire is connected to a metallic plate buried deep inside the earth.

   Reason (R): Earth wire ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, so the user may not get a severe electric shock.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of the Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

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5. Q105 CBSE 2025
   Two statements are ​given below ​– ​one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct ​answer to ​this question from the options ​(a), (b), ​(c) and (d) given below.

   Assertion (A): An electric fuse wire is always connected in parallel with the mainline.

   Reason (R): If an electric current larger than the rated value flows through the electric circuit, the fuse wire melts.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (d) Assertion (A) is false, but Reason (R) is true.

   Step-by-step solution →
6. Q106 CBSE 2025
   In a straight conductor, the current is ​flowing vertically downwards. ​State the ​pattern of the magnetic field lines around ​the conductor. ​Name the rule which helps us to determine the ​direction of the magnetic ​field lines in this case.
   Show answer

   Concentric circles in horizontal planes round the wire, clockwise as seen from above for a downward current; the right-hand thumb rule.

   The magnetic field lines around the conductor are concentric circles centred on the wire, lying in planes at right angles to it — so, the wire being vertical, in horizontal planes. The circles are crowded together close to the wire and become farther apart with distance, showing that the field is strongest near the conductor and weakens away from it. With the current flowing vertically downwards, the lines are directed clockwise as seen from above (anticlockwise as seen from below). The rule used to find this direction is the **right-hand thumb rule** (Maxwell’s corkscrew rule): hold the conductor in the right hand with the thumb pointing along the current, and the curl of the fingers gives the direction of the field lines.

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7. Q107 CBSE 2025
   What ​are ​magnetic ​field ​lines. List two important properties of magnetic field lines.
   Show answer

   Lines along which a free north pole would move; no two intersect, and closer lines mean a stronger field.

   Magnetic field lines are the lines drawn in a magnetic field along which a hypothetical free north pole would move; the tangent at any point on such a line gives the direction of the magnetic field at that point, and the lines together represent the field pictorially. Two important properties: (i) No two magnetic field lines ever intersect one another, because at the point of intersection the field would have two directions at once, which is impossible; (ii) The relative closeness of the field lines shows the relative strength of the field — the field is stronger where the lines are crowded, as near the poles, and weaker where they are far apart. (They are also closed continuous curves, running from the north pole to the south pole outside the magnet and from south to north inside it.)

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8. Q108 CBSE 2025
   How and ​why is an ​electric fuse used ​in an electric circuit ​? ​Briefly describe its ​function.
   Show answer

   A fuse wire in series in the live wire melts on excess current, breaking the circuit and protecting the appliances.

   How: a fuse — a short piece of wire of a metal or alloy of appropriate melting point, usually in a porcelain cartridge — is connected in series with the circuit or appliance, in the live wire, so that the whole current passes through it. Why: to protect the circuit and the appliances from an unduly high current caused by overloading or short-circuiting. Function: if the current rises above the rated value, the heat produced in the fuse wire ($H=I^{2}Rt$) raises its temperature until it melts; this breaks the circuit and stops the current before the wiring or the appliances are damaged.

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9. Q109 CBSE 2025
   State the role of ​an ​electric fuse, used ​in series with an electrical appliance. ​Why should in an electric circuit a fuse with defined ​rating not be replaced by one with a ​larger rating?
   Show answer

   A fuse in series melts on excess current and breaks the circuit; a larger-rated fuse would not melt at a harmful current.

   Role of the fuse: an electric fuse is a safety device connected in series with the appliance. Its wire, of a material of suitable low melting point, carries the whole current of the appliance; if the current exceeds the specified value because of overloading or a short circuit, the heat produced melts the fuse wire and breaks the circuit. The current stops, and the appliance and the wiring are protected from damage and fire. Why not a larger rating: the rating is chosen just above the normal current of the appliance. A fuse of larger rating would melt only at a much larger current, so an excessive current that is harmful to the appliance and the wiring could flow without the fuse melting. The appliance could be damaged, the wires could overheat and a fire could start, so the fuse would no longer protect the circuit.

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10. Q110 CBSE 2025
    Draw ​the pattern of magnetic field lines due to a ​current carrying straight ​conductor. Mark on ​it the direction of current in the conductor and the ​direction of the ​magnetic field developed. Name the rule that helps us ​to determine the ​direction of magnetic field lines in this case.
    Show answer

    Concentric circles round the wire, anticlockwise as seen from above for an upward current; the rule is the right-hand thumb rule.

    The magnetic field lines are concentric circles centred on the conductor, in planes perpendicular to it, drawn farther apart away from the wire. With the current marked upwards along the conductor, the field lines run anticlockwise when seen from above (see the figure). The direction is given by the right-hand thumb rule (Maxwell’s corkscrew rule): hold the conductor in the right hand with the thumb along the current, and the curled fingers show the direction of the field lines.

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11. Q111 CBSE 2025
    What is short circuiting ? ​State ​its possible ​causes. What is likely to happen ​if ​a domestic ​circuit gets short circuited ? Give reason for the justification of your answer.
    Show answer

    Short-circuiting is live–neutral contact; a very large current flows, overheating wires, so a fuse of proper rating melts to break the circuit.

    Short-circuiting: the live wire and the neutral wire come into direct contact, so the current bypasses the appliance through a path of very low resistance and the current in the circuit increases abruptly. Possible causes: damaged insulation of the wires (worn out, burnt or nibbled by rodents), which lets the bare live and neutral wires touch, or a fault in an appliance. What is likely to happen: a very large current flows; the wires overheat, their insulation may melt, sparks and even a fire may occur, and appliances may be damaged. If a fuse of proper rating is in the circuit, it melts and breaks the circuit. Reason: the resistance of the path becomes very small, so by Ohm's law, $I=\frac{V}{R}$, the current becomes very large, and the heat produced, $H=I^{2}Rt$, increases sharply.

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12. Q112 CBSE 2025
    Answer the following questions for a case ​in which a current carrying ​conductor is placed in a uniform magnetic field :

    1. (a)List three factors on which the magnitude of the force acting on the conductor depends.
    2. (b)​When ​is the magnitude of force ​on the conductor maximum ?
    3. (c)Name the rule which helps in ​determining the direction of force on the conductor and give ​its one application.
    Show answer

    Force depends on current, field strength and length in the field; it is maximum at right angles to the field; Fleming's left-hand rule.

    (a) The size of the force depends on (i) the current through the conductor, (ii) the strength of the magnetic field and (iii) the length of the conductor that lies in the field; the force increases when any one of them increases. (It also depends on the angle between the conductor and the field, which is part (b).) (b) The force is maximum when the conductor, that is, the direction of the current, is at right angles to the direction of the magnetic field; it is zero when the conductor lies along the field. (c) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually at right angles; 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. Application: the electric motor works on this principle (so do loudspeakers and measuring instruments such as galvanometers).

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13. Q113 CBSE 2025
    1. (a)State the Right-hand thumb rule.
    2. (b)​A steady current flows ​through a horizontal power line ​from east to west ​direction as shown in the figure. Apply right-hand thumb ​rule to ​determine the direction of magnetic field (i) at a point directly below it, and ​(ii) at a point directly above it.

    Show answer

    Below the wire the field points south; above the wire it points north.

    (a) Right-hand thumb rule: imagine holding a 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. (b) Looking along the power line from its east end, the current flows away from the observer, so by the rule the field lines circle the wire clockwise; facing west, north is on the observer's right. (i) At a point directly below the wire the magnetic field is directed towards the south, from north to south. (ii) At a point directly above the wire it is directed towards the north, from south to north.

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14. Q114 CBSE 2025
    Consider a rectangular ​cardboard having two holes P and Q through which a ​current ​carrying circular loop has been inserted as shown in the ​diagram.

    1. (a)Make this diagram on your answer sheet and draw three magnetic field lines, one each passing through the points 1 (near P), 2 (at the centre of the loop) ​and 3 (near Q).
    2. (b)List two ​factors on ​which the intensity of the magnetic field produced at the centre of the loop depends.
    3. (c)Name the rule you will apply to determine the direction of magnetic field produced due to a current carrying straight conductor.

    Show answer

    Draw circles round P and Q and a straight axial line at the centre; field depends on current and radius; right-hand thumb rule.

    (a) Through point 1: a circle centred on the hole $P$ and passing through $1$. Through point 3: a circle centred on the hole $Q$ and passing through $3$. Through point 2: a straight line perpendicular to the plane of the loop, along its axis — at the centre the circles have become so large that they appear straight. The current comes up out of the board at $P$ and goes down into it at $Q$, so seen from above the circles run anticlockwise round $P$ and clockwise round $Q$, and both point the same way between the holes. (b) The field at the centre depends on the strength of the current through the loop (directly proportional) and on the radius of the loop (inversely proportional) — the number of turns of the coil is a third such factor. (c) The right-hand thumb rule, also called Maxwell's corkscrew rule.

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15. Q115 CBSE 2025
    As shown in ​the figure a small aluminum rod AB is suspended horizontally between the poles of a ​strong horseshoe magnet. This rod is also connected with a battery and a ​key. Study the ​arrangement shown. (a) State Fleming's left-hand rule. (b) Apply Fleming's left-hand rule to determine :

    1. (i)What is observed when a current is passed ​from B to A in the rod ?
    2. (ii)​What is ​observed when a current is passed from A to B in the rod ?
    3. (iii)What is observed when the rod AB is aligned parallel to the magnetic field and current is passed through it from B to A ​? Justify your answer in this case.

    Show answer

    Rod moves left for current B to A, right for A to B; parallel to the field there is no force.

    (a) Fleming's left-hand rule: stretch the thumb, the forefinger and the 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, and hence of the motion, of the conductor. (b) In the figure the S pole is above the rod and the N pole below it, so the field in the gap is vertically upward. (i) With the current from B to A, the rod is displaced towards the left, in the direction of the arrow marked at A. (ii) With the current from A to B, the current is reversed while the field is unchanged, so the force reverses and the rod is displaced towards the right. (iii) With the rod aligned parallel to the magnetic field, no displacement is observed. The force on a current-carrying conductor is $F=BIL\sin \theta$, where $\theta$ is the angle between the conductor and the field; it is maximum when the conductor is perpendicular to the field and zero when the conductor is parallel to it, since $\sin 0^{\circ }=0$.

    Step-by-step solution →
16. Q116 CBSE 2025
    (a) ​Draw a labelled diagram ​to show the ​pattern of magnetic field lines on a horizontal white board due to a straight current carrying conductor passing ​perpendicular through its centre. If the direction of ​current in the ​conductor is vertically downwards, mark the direction of

    1. (i)current, and
    2. (ii)magnetic field lines. (b) ​State the right hand thumb rule and check whether the directions marked on the diagram are ​in accordance with this rule.
    Show answer

    Concentric circles with clockwise arrows seen from above for downward current; the right-hand thumb rule confirms the directions.

    (a) The field lines are concentric circles on the board, centred on the conductor and closer together near it. The current is marked by a downward arrow on the conductor (a cross ⊗ where it enters the board, seen from above), and the field lines are marked clockwise as seen from above. (b) Right-hand thumb rule: if a current-carrying straight conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers wrap around the conductor in the direction of the magnetic field lines. With the thumb pointing downwards, the fingers curl clockwise as seen from above, so the directions marked on the diagram are in accordance with the rule.

    Step-by-step solution →
17. Q117 CBSE 2025
    1. (a)Name and state the rule which determines the force ​on a current carrying ​conductor placed in a uniform magnetic field.
    2. (b)Consider the following three ​diagrams in which the ​entry of a positive charge $(+Q)$ in a magnetic field ​is shown. Identify giving ​reason the case in which the force experienced by the charge is (i) maximum, and (ii) minimum.

    Show answer

    Fleming's left-hand rule; force is maximum in diagram III (charge at right angles to field) and zero in diagram I (along field).

    (a) 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 on the conductor. (b) (i) The force is maximum in diagram III, because there the charge moves at right angles to the magnetic field. (ii) The force is minimum — zero — in diagram I, because there the charge moves along the magnetic field lines. In II the charge moves at an angle between $0^{\circ }$ and $90^{\circ }$ to the field, so the force on it lies between these two values.

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18. Q118 CBSE 2025
    1. (i)List two ​important safety ​measures commonly used in ​domestic electric circuits and the appliances ​such as electric irons/ovens.
    2. (ii)The ​power rating of an electric appliance is 220 V; 2 ​kW. If it is used in a room having electric circuit ​of current ​rating of 5 A, what result do you expect ? Give reason for your answer with necessary calculations.
    Show answer

    Fuse and earthing; the appliance needs $9.09$ A against the 5 A rating, so the fuse melts and the circuit breaks.

    (i) Two safety measures are: an electric fuse or MCB of proper rating connected in series in the live wire, which melts and breaks the circuit when the current exceeds the safe limit; and earthing, in which the metallic body of the appliance is joined to the earth wire through the third pin of the three-pin plug, so that any leakage current passes to the earth and the user is not given a shock. (ii) The current needed is $I=\frac{P}{V}=\frac{2000}{220}=9.09$ A, which is much more than the $5$ A the circuit is rated for. The circuit will therefore be overloaded and its $5$ A fuse will melt and break the circuit, so the appliance will stop working; without a proper fuse the wiring would overheat and could cause a fire. Equivalently, at $5$ A the circuit can deliver at most $220\times 5=1100$ W, far less than the $2000$ W demanded.

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19. Q119 CBSE 2025
    Name and state ​the rule to determine the direction of ​a

    1. (i)magnetic field produced ​around a straight conductor carrying a steady ​current.
    2. (ii)force experienced ​by a current carrying straight conductor ​placed perpendicular to ​a uniform magnetic field.
    Show answer

    (i) Right-hand thumb rule gives the field around a straight conductor; (ii) Fleming's left-hand rule gives the force on a conductor in a field.

    (i) Right-hand thumb rule. Hold the straight current-carrying conductor in your right hand with the thumb stretched along the direction of the current; the fingers wrapped round the conductor then give the direction of the magnetic field lines, which are concentric circles around the conductor. (ii) 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 experienced by the conductor.

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20. Q120 CBSE 2025
    1. (a)​“The third ​wire of earth connection is very ​important in domestic electric ​appliances.” ​Justify this statement.
    2. (b)List two precautions to be taken ​to avoid the overloading of domestic electric circuits.
    Show answer

    The earth wire carries leaking current safely to the ground, preventing shock; avoid overloading by not crowding sockets or circuits.

    (a) The earth wire, insulated in green, joins the metal body of an appliance through the third pin of the plug to a metal plate buried deep in the earth, giving a conducting path of very low resistance to the earth. If the live wire's insulation fails and the live wire touches the metal body, the body would be at a high potential and would give a severe shock to anyone touching it. With the earth connection the body stays at the potential of the earth and the leakage current flows through the earth wire, whose resistance is a fraction of an ohm, rather than through the person, whose resistance is thousands of ohms; the large current also blows the fuse and disconnects the appliance. This is why the third wire is essential in metal-bodied, high-power appliances such as an electric iron, a toaster or a refrigerator. (b) Two precautions against overloading: (i) Do not connect too many appliances to a single socket, that is, avoid running several appliances from one socket through a multi-plug or an extension board. (ii) Do not switch on too many high-power appliances, such as a heater, a geyser and an air conditioner, on the same circuit at the same time; use separate circuits, each with a fuse or MCB of the proper rating and wires of adequate thickness.

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