Class 10 Science · Chapter 12

Magnetic Effects of Electric Current

170 Class 10 Science questions on Magnetic Effects of Electric Current from the NCERT textbook, NCERT Exemplar and CBSE board papers 2023–2026, 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 5 of 9

Q81 CBSE 2026
1. (i)Draw a diagram showing the magnetic field lines around a bar magnet. Write any two characteristics of magnetic field lines.
2. (ii)Write the statement of Right hand thumb rule.
3. (iii)The concentric circles representing the magnetic field around a current carrying straight wire become larger and larger as we move away from the wire. How does magnetic field change on these concentric circles ?
Show answer

A bar magnet's field lines are closed curves; round a straight wire the field is constant along each circle and weakens outwards as $B \propto \frac{1}{r}$ .
(i) The field lines of a bar magnet are closed curves: outside the magnet they emerge from the north pole, curve round and enter the south pole, and inside the magnet they run from the south pole to the north pole; they are crowded near the poles and widely spaced near the middle, as the diagram shows. Two characteristics - magnetic field lines never intersect one another, because a compass placed at a crossing would have to point in two directions at once; and the lines are crowded where the field is strong and farther apart where it is weak, the tangent at any point giving the direction of the field there. (ii) Right hand thumb rule: if a current-carrying straight conductor is held in the right hand with the thumb pointing along the direction of the current, then the fingers wrapped round the conductor give the direction of the magnetic field lines. (iii) On any one circle the field has the same magnitude at every point, since all those points are the same distance from the wire, and its direction is along the tangent there. From one circle to the next the field becomes weaker as the circles become larger, because $B = \frac{μ _{0} I}{2 π r}$ , that is $B \propto \frac{1}{r}$ : a circle of twice the radius carries half the field.

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Q82 CBSE 2026
1. (i)List any two features of the electric current used in the houses of India.
2. (ii)Write any two differences between direct current and an alternating current.
3. (iii)How will you identify live wire and neutral wire in a domestic electric circuit ?
Show answer

Household supply is alternating current at 50 Hz; unlike direct current it reverses direction; live wire is red, neutral black.
(i) It is alternating current: its direction changes periodically, reversing after every $\frac{1}{100}$ s; and its frequency is $50$ Hz. (It is supplied at a potential difference of $220$ V between the live and the neutral wire.) (ii) Direct current flows in one direction only, whereas alternating current reverses its direction periodically (every $\frac{1}{100}$ s in India); and direct current is obtained from cells and batteries, whereas alternating current is obtained from a.c. generators at power plants, through the mains. (Also, alternating current can be transmitted over long distances without much loss of energy, because transformers can step its voltage up for transmission and down again for use.) (iii) By the colour of the insulation: the live wire has red insulation and the neutral wire has black insulation (the earth wire is green). A line tester confirms it: its neon lamp glows when the tip touches the live wire, which is $220$ V above earth potential, and stays dark on the neutral wire, which is at nearly the potential of the earth.

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Q83 CBSE 2026
1. (i)State the rule which gives the direction of force acting on a current carrying conductor placed in a uniform magnetic field.
2. (ii)Name any two devices which work on the basis of an interaction between magnetic field and current carrying conductor.
3. (iii)Observe the given diagrams : Comment on the magnitude of force on electron in both the cases and give reason for your answer.
Show answer

The force on the electron is maximum in case (I) and zero in case (II); Fleming's left-hand rule gives its direction.
(i) 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 along the magnetic field and the middle finger along the current, the thumb points in the direction of the force on the conductor. (ii) Electric motor and loudspeaker. (A moving-coil galvanometer or ammeter is an equally good answer.) (iii) The force is maximum in case (I) and zero in case (II). Since $F = e v B sin θ$ , in case (I) the electron moves at right angles to the field, $θ = 9 0^{\circ}$ and $sin 9 0^{\circ} = 1$ , giving $F = e v B$ ; in case (II) the electron moves along the field, $θ = 0^{\circ}$ and $sin 0^{\circ} = 0$ , so no magnetic force acts on it.

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Q84 CBSE 2026
1. (i)Draw the pattern of magnetic field lines through and around a current-carrying circular loop.
2. (ii)State the rule to find out the direction of the magnetic field inside and around the circular loop.
3. (iii)Give reasons : (I) Why should a burnt-out fuse be replaced by another fuse of identical rating only, in an electric circuit ? (II) Why is soft iron-core used in making an electromagnet ?
Show answer

Right-hand thumb rule gives the field direction; only an identical fuse rating protects the circuit; soft iron makes the electromagnet strong yet temporary.
(i) Close to the wire the field lines are concentric circles round each point where the loop passes through the paper - anticlockwise round the point where the current comes out of the paper and clockwise round the point where it goes in (see the figure). The circles grow larger away from the wire, and inside the loop they all point the same way; near the centre they become nearly straight, parallel lines at right angles to the plane of the loop. (ii) Right-hand thumb rule: hold the current-carrying conductor in the right hand with the thumb pointing in the direction of the current; the fingers wrapped round the conductor give the direction of the magnetic field lines. Applied to each part of the loop, every part gives the field in the same direction inside the loop. (iii) (I) The rating of a fuse is chosen just above the normal current of the circuit. A fuse of higher rating would not melt when an unduly high current flows, so the circuit and the appliances would not be protected; a fuse of lower rating would melt even at the normal current. So a burnt-out fuse must be replaced by one of the same rating. (II) Soft iron becomes strongly magnetised when current flows through the coil, which makes the electromagnet much stronger, and it loses its magnetism almost as soon as the current is switched off, so the electromagnet works only while the current flows.

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Q85 CBSE 2026
1. (i)(I) In the given circuit diagram, a battery $B$ , a key $K$ , a resistance $R$ and a thick copper wire XY are connected in series and a compass is placed near the wire. What is the purpose of this arrangement ? (II) What conclusion do you draw from it ?
2. (ii)Give reasons : (I) There is either a convergence or a divergence of magnetic field lines near the ends of a current-carrying straight solenoid. (II) The current-carrying solenoid, when suspended freely, aligns along a particular direction. (III) The burnt-out fuse should be replaced by another fuse of identical rating.
Show answer

A current produces a magnetic field; a solenoid acts like a bar magnet; a replacement fuse needs the same rating.
(i) (I) The arrangement shows the magnetic effect of electric current: when the key $K$ is closed and current flows through the thick copper wire XY, the compass needle placed near the wire is deflected. (II) A current flowing through a conductor produces a magnetic field around it, so electricity and magnetism are linked; since the deflection reverses when the current is reversed, the direction of the field depends on the direction of the current. (ii) (I) A current-carrying solenoid behaves like a bar magnet: its field lines, parallel inside, come out of the end acting as the north pole and spread apart (diverge), and crowd together (converge) where they enter the end acting as the south pole. (II) A current-carrying solenoid behaves like a bar magnet with a north and a south pole at its ends, so when suspended freely the Earth's magnetic field turns it, like a compass needle, until it comes to rest along the north–south direction. (III) A fuse's rating is the largest current its circuit is designed to carry. A fuse of higher rating would not melt when too large a current flows (overloading or a short circuit), so the wiring and appliances could be damaged or catch fire; a fuse of lower rating would melt even at the normal current. Only a fuse of identical rating protects the circuit and still lets it work normally.

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Q86 CBSE 2026
1. (i)Draw a schematic diagram of a domestic electric circuit which includes the following devices : (I) A fuse (II) A power meter (III) One light point (IV) A power plug
2. (ii)Why is it necessary to connect an earth wire to the electrical appliances having metallic covers ?
Show answer

The mains pass through fuse, meter and switch to parallel circuits; the earth wire prevents severe shock from a metal cover.
(i) In the schematic, the live wire (red) and the neutral wire (black) from the pole pass through the main fuse (in the live wire) and the power meter (kWh meter), then through the main switch to the distribution box. From there separate circuits run in parallel, each with its own fuse in the live wire: a $5$ A circuit to the light point, with its switch in the live wire, and a $15$ A circuit to the power plug (a three-pin socket), with its switch in the live wire and its third pin joined to the earth wire (green), which ends at a metal plate buried in the ground. (ii) If the live wire touches the metallic cover because of damaged insulation, the cover comes to the mains voltage and anyone who touches it gets a severe shock. The earth wire provides a low-resistance path for this leakage current to the earth, so the cover stays at the potential of the earth and the user does not get a severe electric shock; the large current in this path also blows the fuse and cuts off the supply.

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Q87 CBSE 2026
1. (i)With the help of a diagram, show that a current-carrying conductor placed in an external magnetic field, experiences a force. Indicate the direction of the field, current and force clearly.
2. (ii)The diagram given below shows an electron moving in a uniform magnetic field. (I) What will be the direction of the force acting on the electron ? (II) What will happen to the direction of the force acting on the electron, if the direction of the magnetic field as well as the direction of the motion of the electron, both are reversed ?
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A current-carrying rod in a field is pushed sideways; the electron's force is into the paper and unchanged if field and motion both reverse.
(i) A light aluminium rod is hung across the field between the poles of a horseshoe magnet - the S pole above and the N pole below, so the field points upward - and is connected to a battery through a key. As soon as the current flows (out of the page in the diagram) the rod is pushed sideways, to the left, which shows that a current-carrying conductor placed in a magnetic field experiences a force. The three directions are: field upward, from N to S; current out of the page; force to the left, perpendicular to both, as given by Fleming's left-hand rule (see the diagram). (ii)(I) The electron moves upward, so the conventional current is downward; with the field pointing to the left, Fleming's left-hand rule gives a force perpendicular to the plane of the paper, directed into the paper, away from the reader. (II) The direction of the force does not change - it is still into the plane of the paper. Reversing the field alone would reverse the force and reversing the motion alone would reverse it as well, so reversing both leaves it exactly as it was.

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Q88 CBSE 2026
1. (i)With the help of a diagram, describe an activity in brief to show that a current-carrying straight conductor produces a magnetic field around it.
2. (ii)Two straight current-carrying conductors (A) and (B) are shown in the figures below : (I) Mark the direction of the magnetic fields around these current-carrying conductors (A) and (B). (II) Compare the strengths of magnetic fields produced (1) at points P and Q and (2) at points Q and R due to these current-carrying conductors, qualitatively.
Show answer

Filings and compass show circular field lines round a current-carrying wire; the field is stronger at Q than at P or R.
(i) Pass a thick copper wire vertically through the centre of a horizontal cardboard and connect it in series with a battery, a plug key, a rheostat and an ammeter. Place a small compass on the cardboard near the wire and sprinkle iron filings uniformly on the cardboard. When the key is inserted and current passes through the straight conductor, the compass needle placed near it shows a deflection, and it deflects the opposite way when the current is reversed. On tapping the cardboard gently, the iron filings arrange themselves in concentric circles around the wire, and the compass needle sets itself along these circles. With the key out, the needle points north-south again. This shows that the current-carrying straight conductor produces a magnetic field around it, whose field lines are concentric circles centred on the conductor. (ii) (I) By the right-hand thumb rule, the field lines around (A), whose current flows upwards, run anticlockwise when seen from above; those around (B), whose current flows downwards, run clockwise when seen from above, on both circles. (II) (1) The field at Q is stronger than the field at P: both points are $2$ cm from their wires, but (B) carries the larger current ( $2$ A against $1$ A). (2) The field at Q is stronger than the field at R: both are due to the same current ( $2$ A), but R is $4$ cm from the wire while Q is only $2$ cm from it.

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Q89 CBSE 2026
1. (i)Write the name and statement of the rule used to determine the direction of the : (I) force experienced by a straight current-carrying conductor placed in a uniform magnetic field perpendicular to the field. (II) magnetic field produced around a straight conductor carrying electric current.
2. (ii)Two straight current-carrying conductors (A) and (B) are shown in the figures below : (I) Mark the direction of the magnetic fields around these current-carrying conductors (A) and (B). (II) Compare the strengths of magnetic fields produced (1) at points P and Q and (2) at points Q and R due to these current-carrying conductors, qualitatively.
Show answer

Fleming's left-hand rule; right-hand thumb rule; the field is anticlockwise round A, clockwise round B, and stronger at Q than at P or R.
(i) (I) 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, the thumb points in the direction of the force (the motion) on the conductor. (II) Right-hand thumb rule: imagine holding the current-carrying straight conductor in the right hand with the thumb pointing in the direction of the current; the fingers then wrap around the conductor in the direction of the magnetic field lines. (ii) (I) Around (A), where the current flows upwards, the field lines are anticlockwise circles as seen from above; around (B), where the current flows downwards, they are clockwise circles as seen from above - see the marked figure. (II) (1) The field at Q is stronger than the field at P: both points are $2$ cm from their conductors, but (B) carries the larger current ( $2$ A against $1$ A). (2) The field at Q is stronger than the field at R: both are due to the same current of $2$ A, but Q is nearer the conductor ( $2$ cm against $4$ cm).

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Q90 CBSE 2026
1. (i)Draw a diagram, showing the magnetic field lines in and around the current carrying solenoid. Write any two salient features of these lines.
2. (ii)What is an electromagnet and how is it made ?
Show answer

A solenoid's field is uniform inside and like a bar magnet's outside; an electromagnet is a soft iron core in a current-carrying coil.
(i) The diagram shows the field lines of a current-carrying solenoid: inside the coil they are straight, parallel and equally spaced, running from the south end to the north end, and outside they leave the north end, curve round the coil and enter the south end, so that each line is a closed curve. Two salient features - the field inside the solenoid is uniform, the same in magnitude and direction at every point there, which is why those lines are parallel and equally spaced; and the pattern outside is exactly that of a bar magnet, one end of the coil behaving as a north pole and the other as a south pole, with no two lines ever intersecting. (ii) An electromagnet is a temporary magnet made by passing an electric current through a coil of insulated wire wound on a soft iron core; the core stays magnetised only as long as the current flows. It is made by winding a long insulated copper wire closely round a rod of soft iron in the form of a solenoid and connecting the ends of the wire to a battery through a plug key. Closing the key magnetises the core, which then behaves as a strong magnet with a north and a south pole; opening the key leaves it with almost no magnetism. Its strength is increased by increasing the current or the number of turns, and its poles are interchanged by reversing the current.

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Q91 CBSE 2026
1. (i)Why is fuse an important component in our electric circuits ?
2. (ii)Distinguish between overloading and short-circuiting of a circuit.
3. (iii)Giving reason explain what type of materials are used in fuse wires.
Show answer

A fuse melts to break the circuit when current is excessive; its wire is a tin-lead alloy of low melting point and high resistivity.
(i) A fuse is a safety device joined in series with the live wire. When the current rises above the safe value, through overloading or a short circuit, the heat produced ( $H = I^{2} R t$ ) melts the thin fuse wire and breaks the circuit, so the current stops before the wiring or the appliances are damaged and before a fire can start. (ii) In overloading, too many or too powerful appliances are run from one circuit (or the supply voltage rises accidentally), so the current drawn exceeds the rated value while still flowing through the appliances; in short-circuiting, the live and neutral wires touch directly, the appliances are bypassed, the resistance of the path falls to nearly zero and by $I = \frac{V}{R}$ an enormous current flows at once. (iii) The fuse wire is a short, thin wire of an alloy of low melting point, usually an alloy of tin and lead. Its low melting point lets it melt quickly the moment the current exceeds the rated value, and its high resistivity with a small cross-section ( $R = ρ \frac{L}{A}$ ) makes its resistance much greater than that of the copper wiring, so by $H = I^{2} R t$ it heats fastest and is the first thing in the circuit to give way.

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Q92 CBSE 2026
1. (i)List three possible reasons of short-circuiting in an electric circuit.
2. (ii)In case of overload, will the fuse protect to given electric circuit from damage ? Justify your answer.
3. (iii)For an electric heater rated as 220 V, 2200 W, what should be the minimum rating of fuse used with it ?
Show answer

No, the fuse sits in the neutral wire; the heater draws 10 A, so its fuse rating should be slightly more than 10 A.
(i) Three possible reasons for short-circuiting: (1) direct contact between the live wire and the neutral wire, for instance through a fault inside an appliance or a loose joint; (2) damaged or worn-out insulation on the wires, which lets the bare live and neutral wires touch; (3) overloading — too many appliances drawing current through one circuit overheats the wires, which can melt their insulation and let the live and neutral wires touch. (ii) No. In the circuit shown the fuse is connected in the neutral wire, but a fuse must be connected in series with the live wire. Even if an overload melts this fuse and stops the current, the heater and its wiring stay joined to the live wire at $220$ V, so the circuit is not made safe, and a leakage from the live wire to earth would not blow the fuse at all. (iii) $I = \frac{P}{V} = \frac{2200}{220} = 10$ A. The fuse must carry this $10$ A in normal use without melting, so its minimum rating should be slightly more than $10$ A.

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Q93 CBSE 2025
A steady current flows through a thick horizontal straight wire from east to west. The direction of the magnetic field produced at a point above the wire is towards
1. (a)North
2. (b)South
3. (c)East
4. (d)West
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(a) North

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Q94 CBSE 2025
In domestic electric circuits, the colour of insulation covers of wires in the cables of electric iron/electric toaster is generally :
1. (a)red for live wire, green for neutral wire and black for earth wire
2. (b)red for live wire, black for neutral wire and green for earth wire
3. (c)green for live wire, black for neutral wire and red for earth wire
4. (d)green for live wire, red for neutral wire and black for earth wire
Show answer

(b) red for live wire, black for neutral wire and green for earth wire

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Q95 CBSE 2025
Which one of the following statements is not true about a bar magnet ?
1. (a)It sets itself in north-south direction when suspended freely.
2. (b)It has attractive power for iron filings.
3. (c)It produces magnetic field lines.
4. (d)The direction of magnetic field lines inside a bar magnet is from its north pole to its south pole.
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(d) The direction of magnetic field lines inside a bar magnet is from its north pole to its south pole.

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Q96 CBSE 2025
The strength of the magnetic field inside a current carrying long straight solenoid is :
1. (a)maximum at its centre.
2. (b)minimum at its centre.
3. (c)maximum at the ends and minimum at its centre.
4. (d)uniform throughout its length.
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(d) uniform throughout its length.

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Q97 CBSE 2025
The strength of magnetic field produced inside a long straight current carrying solenoid does not depend upon :
1. (a)number of turns in the solenoid
2. (b)direction of current flowing through the solenoid
3. (c)material of the core filled inside the solenoid
4. (d)radius of the coil of the solenoid
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(d) radius of the coil of the solenoid

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Q98 CBSE 2025
The strength of the magnetic field produced inside a current carrying long straight solenoid does not depend upon :
1. (a)Area of cross-section of the tube of the solenoid
2. (b)Number of turns per unit length in the solenoid
3. (c)Direction of current flowing through the coil of the solenoid
4. (d)Material of the core of the solenoid
Show answer

(a) Area of cross-section of the tube of the solenoid

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Q99 CBSE 2025
A uniform magnetic field
1. (a)always exerts a force on a current carrying conductor.
2. (b)never exerts a force on a current carrying conductor.
3. (c)exerts a force only when current flows through a conductor along the direction of the field.
4. (d)exert a force only when current flows through a conductor at right angles to the field.
Show answer

(d) exert a force only when current flows through a conductor at right angles to the field.

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Q100 CBSE 2025
Two statements are given — 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): No two magnetic field lines are found to cross each other.
Reason (R): The compass needle cannot point towards two directions at the point of intersection of two magnetic field lines.
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.
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(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

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