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 10 of 14

1. Q181 CBSE 2023
   These consist of two statements ​– Assertion (A) and ​Reason ​(R). Answer this question ​selecting the appropriate option given below.

   Assertion (A): A current carrying straight conductor experiences a force when placed perpendicular to the direction of magnetic field.

   Reason (R): The net charge on a current carrying conductor is always zero.

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

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

   Step-by-step solution →
2. Q182 CBSE 2023
   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): Two magnetic field lines around a current carrying straight wire do not intersect each other.

   Reason (R): The magnitude of the magnetic field produced at a given point increases as the current through the wire increases.

   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

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

   Step-by-step solution →
3. Q183 CBSE 2023
   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): Magnetic fields interact with moving charges and not with charges at rest.

   Reason (R): Charges produce magnetic field only when they move.

   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

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

   Step-by-step solution →
4. Q184 CBSE 2023
   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): A current carrying straight solenoid, when suspended freely rests in geographical north-south direction.

   Reason (R): Earth behaves as a huge magnet which has the north pole towards the geographical south, whereas the current carrying solenoid behaves like a bar magnet.

   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

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

   Step-by-step solution →
5. Q185 CBSE 2023
   What will happen ​if ​an electric ​oven of rating 3 kW; 220 V ​is ​operated in a domestic electric circuit (220 V) that has a current rating of 10 A ? ​Give ​reason to justify your answer.
   Show answer

   The oven draws about 13.6 A, more than the 10 A rating, so the circuit is overloaded and the fuse melts.

   The current the oven draws is $I=\frac{P}{V}=\frac{3000\text{W}}{220\text{V}}\approx 13.6$ A, which is more than the $10$ A the circuit is rated for. The circuit will therefore be overloaded: the fuse in the circuit melts and breaks it, so the supply is cut off and the oven does not work. The reason is that a $10$ A circuit can safely deliver only $220\times 10=2200$ W, that is $2.2$ kW, while the oven needs $3$ kW; if the excess current were allowed to flow the heat produced, $H=I^{2}Rt$, would overheat the wiring and could cause a fire.

   Step-by-step solution →
6. Q186 CBSE 2023
   Consider ​a circular loop of thick copper ​wire lying ​horizontally ​on ​a table. Let the current pass through the loop anticlockwise. Draw the magnetic field lines to show the direction and the pattern ​of the magnetic field inside ​and outside the loop.
   Show answer

   For an anticlockwise current seen from above, the field points up through the loop and down outside it.

   Seen from above with the current anticlockwise, the magnetic field inside the loop points vertically upward, out of the table, and outside the loop it points downward, into the table. Near the wire the field lines are concentric circles round it; they become larger further away, and at the centre of the loop they are nearly straight lines perpendicular to the plane of the loop. Each line is a closed curve that goes up through the loop and comes back down outside it (see the diagram).

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7. Q187 CBSE 2023
   Differentiate between direct ​and alternating ​current. ​Name the type of ​current ​produced ​by the power plants in our country. Also ​state its frequency.
   Show answer

   DC flows one way and AC reverses; Indian power plants produce AC of frequency 50 Hz.

   Direction: direct current (DC) flows in one direction only, while alternating current (AC) reverses its direction after equal intervals of time. Source: DC is obtained from cells and batteries, while AC is produced by the generators of power stations. Transmission: AC can be transmitted over long distances without much loss of energy, because its voltage can be stepped up and down by transformers; DC cannot be stepped up and down by a transformer. The power plants in India produce alternating current, and its frequency is $50$ Hz (it changes direction every $\frac{1}{100}$ s).

   Step-by-step solution →
8. Q188 CBSE 2023
   1. (a)State Fleming’s ​left-hand ​rule.
   2. (b)​An electron enters ​a magnetic ​field at right angles to it as shown in the following ​diagram. Use Fleming’s left-hand rule ​to determine the direction of force experienced ​by the electron.

   Show answer

   (a) Fleming's left-hand rule relates field, current and force; (b) the force on the electron is into the page.

   (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 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 the conductor. (b) The electron moves up the page, so the current is down the page. With the forefinger to the left (field) and the middle finger down (current), the thumb points into the page: the force on the electron is perpendicular to the plane of the paper, directed into it.

   Step-by-step solution →
9. Q189 CBSE 2023
   State the ​rule to determine the direction of a

   1. (a)magnetic field produced around ​a straight conductor carrying current and ​
   2. (b)force experienced by ​a current ​carrying straight conductor placed in ​a ​magnetic field which is perpendicular ​to it.
   Show answer

   (a) Right-hand thumb rule gives the field direction; (b) Fleming's left-hand rule gives the direction of the force.

   (a) Right-hand thumb rule: hold the straight conductor in your right hand with the thumb pointing in the direction of the current; the way the fingers curl round the conductor then gives the direction of the magnetic field lines, which are concentric circles round the wire. (b) Fleming’s left-hand rule: stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular; the forefinger points along the magnetic field, the middle finger along the current, and the thumb then points in the direction of the force on the conductor.

   Step-by-step solution →
10. Q190 CBSE 2023
    Draw magnetic field lines produced around a straight ​current ​carrying conductor passing through a cardboard. How will the strength of the ​magnetic field ​change when the point ​where ​magnetic field is to be determined is moved ​away from the conductor ?
    Show answer

    The field lines are concentric circles round the wire, and the field becomes weaker as the point moves away from the conductor.

    The field lines are concentric circles centred on the wire, lying on the cardboard in planes perpendicular to the wire (see the figure). For a current flowing upwards they run anticlockwise as seen from above, by the right-hand thumb rule, and they are drawn farther apart the farther they are from the wire. As the point is moved away from the conductor, the strength of the magnetic field decreases.

    Step-by-step solution →
11. Q191 CBSE 2023
    Explain ​the meaning of overloading of an electrical circuit. List two possible causes due to which overloading may occur in household ​circuits. ​Write one ​preventive measure that ​should be taken to avoid overloading of ​domestic circuits.
    Show answer

    Overloading is a current beyond the safe rating, caused by too many appliances or a voltage rise; a proper fuse protects the wiring.

    Overloading means that a current larger than the safe value for which the circuit and its wiring are rated is being drawn through it. Since the heat produced is $H=I^{2}Rt$, the excess current heats the wires very rapidly, the insulation may melt and a fire may break out. Two causes in household circuits: (1) connecting too many appliances, especially high power ones such as a heater, geyser, iron or oven, to a single socket, so that the currents in the parallel branches add up beyond the rating of the wire; (2) an accidental rise in the supply voltage, which raises the current drawn by every appliance since $I=V/R$. Preventive measure: do not connect too many appliances to one socket, and always connect an electric fuse of the proper rating in series in the circuit, so that it melts and breaks the circuit before the wiring can be damaged.

    Step-by-step solution →
12. Q192 CBSE 2023
    What is a ​solenoid? When does a ​solenoid ​behave as ​a magnet? Draw the pattern of the ​magnetic field ​produced inside ​it showing the directions of the magnetic field lines.
    Show answer

    A solenoid is a closely wound coil of insulated wire; it behaves as a magnet only while current flows, with parallel field lines inside.

    A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. It behaves as a magnet only when an electric current is passed through it: the field pattern it then produces is exactly like that of a bar magnet, one end of the coil acting as the north pole and the other as the south pole, and the magnetism disappears as soon as the current is switched off. Inside the solenoid the magnetic field lines are straight lines parallel to the axis, equally spaced, and all pointing the same way — from the south end towards the north end. Equally spaced parallel lines mean that the field inside is uniform, that is, the same in magnitude and direction at every point inside the coil (see the diagram).

    Step-by-step solution →
13. Q193 CBSE 2023
    What is a solenoid? ​How does a current carrying solenoid ​behave when suspended ​freely and ​why? Give its one ​main ​use.
    Show answer

    A solenoid is a closely wound coil; suspended freely it rests north-south like a bar magnet, and it is used to make an electromagnet.

    A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. When a current is passed through it, the field inside is strong and uniform and the field pattern outside is exactly that of a bar magnet, with one end acting as the north pole and the other as the south pole. Therefore, when a current-carrying solenoid is suspended freely it comes to rest along the north-south direction, just as a freely suspended bar magnet does, because the earth’s magnetic field exerts a torque on it until its magnetic axis lies along the magnetic meridian. Its one main use is to magnetise a piece of magnetic material such as soft iron placed inside it, that is, to make an electromagnet.

    Step-by-step solution →
14. Q194 CBSE 2023
    What ​is a solenoid ? ​Draw a diagram to ​show the pattern of magnetic field ​around a ​current carrying solenoid. Name ​the region ​of uniform magnetic field.
    Show answer

    A solenoid is a closely wound cylindrical coil of insulated wire; the magnetic field is uniform inside it.

    A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. The magnetic field lines of a current-carrying solenoid are parallel straight lines inside it; outside, they form the pattern of a bar magnet, leaving one end (the north pole) and curving round to enter the other end (the south pole), so that each line is a closed curve (see the diagram). The field is uniform inside the solenoid, where the lines are parallel and equally spaced: the magnetic field has the same strength and direction at all points there, away from the ends.

    Step-by-step solution →
15. Q195 CBSE 2023
    1. (a)List two factors on which the magnitude of magnetic field ​produced ​by a current ​carrying straight conductor ​depends.
    2. (b)State the rule which determines ​the direction of magnetic ​field in the above case.
    3. (c)Draw the pattern ​of magnetic field lines produced in this case.
    Show answer

    The field depends on the current and the distance from the wire; the right-hand thumb rule gives its direction; lines are concentric circles.

    (a) The magnitude of the magnetic field at a point near a straight current-carrying conductor depends on (1) the current through the conductor: the field increases as the current increases; and (2) the distance of the point from the conductor: the field decreases as the distance increases. (b) 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 give the direction of the magnetic field lines. (c) The field lines are concentric circles centred on the conductor, in planes perpendicular to it (see the figure). For a current flowing upwards they run anticlockwise when seen from above, and they are drawn farther apart with increasing distance from the conductor, where the field is weaker.

    Step-by-step solution →
16. Q196 CBSE 2023
    1. (i)State the rule used to find the force acting on a current ​carrying conductor placed in a magnetic field.
    2. (ii)Given below are three diagrams showing entry of ​an electron in ​a magnetic field. Identify the case in which ​the force ​will be ​(1) maximum and (2) ​minimum respectively. Give reason for your ​answer.

    Show answer

    Fleming's left-hand rule; the force is maximum in case (i), where the electron enters at $90^{\circ }$ to the field, and zero in case (iii).

    (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, then the thumb gives the direction of the force acting on the conductor. (ii) (1) The force is **maximum** in case (i), because there the electron enters at right angles ($90^{\circ }$) to the magnetic field, and the force $F=qvB\sin \theta$ is greatest when $\sin \theta =1$. (2) The force is **minimum** (zero) in case (iii), because there the electron moves parallel to the magnetic field, so $\theta =0^{\circ }$ and $\sin \theta =0$. In case (ii) the electron enters obliquely, so the force lies between these two values.

    Step-by-step solution →
17. Q197 CBSE 2023
    1. (i)Why ​is an alternating ​current ​(A.C.) considered to be advantageous over direct current (D.C.) for the ​long distance transmission ​of electric power ?
    2. (ii)How is the type of current used in household supply different ​from the one given by a battery of dry cells ?
    3. (iii)How does an electric fuse prevent ​the electric circuit and the appliances from a possible damage due to short circuiting or overloading.
    Show answer

    AC voltage can be stepped up to cut line loss; household supply is AC, cells give DC; a fuse melts to break the circuit.

    (i) An alternating voltage can be stepped up by a transformer to a very high value for transmission and stepped down again at the consumer's end. Since $P=VI$, a high transmission voltage means a small current, and the energy lost as heat in the line is $H=I^{2}Rt$, which falls as the **square** of the current; ten times the voltage therefore cuts the loss to a hundredth. A transformer works only with a changing current, so direct current cannot be stepped up and down in this way and would lose far more energy over the same distance. (ii) The household supply is alternating current, whose direction reverses regularly; in India its frequency is $50$ Hz, so it changes direction every $1/100$ second. A battery of dry cells gives direct current, which flows in one direction only and never reverses. (iii) A fuse is a short piece of wire of low melting point and suitable resistivity connected in series in the live wire, with a rating just above the normal current. During a short circuit or an overload the current becomes very large, and since the heat produced is $H=I^{2}Rt$ the fuse wire melts before anything else does. The circuit is broken and the supply cut off, so the wiring and the appliances are saved from overheating, damage and fire.

    Step-by-step solution →
18. Q198 CBSE 2023
    (i) A straight cylindrical conductor is ​suspended ​with its axis perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards ​left when a current is passed through it. What will happen to the displacement of the conductor if the

    1. (1)​current ​through it is increased ?
    2. (2)horse-shoe magnet is replaced by another stronger horse-shoe magnet ?
    3. (3)direction of current through it is reversed ​? (ii) Name and state the rule for determining the ​direction of force on ​a current carrying conductor in a magnetic field.
    Show answer

    A larger current or stronger magnet increases the displacement; reversing the current reverses it; Fleming's left-hand rule gives the direction.

    (1) The force is $F=BIl$, so increasing the current increases the force: the conductor is displaced further, still towards the left. (2) A stronger magnet means a larger $B$, so the force again increases: the displacement is larger, still towards the left. (3) Reversing the current reverses the direction of the force but not its size: the conductor is now displaced towards the right, by the same amount as before. (ii) The rule is Fleming's left-hand rule. Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular to one another; if the forefinger points along the magnetic field and the middle finger along the current, the thumb points along the force on the conductor.

    Step-by-step solution →
19. Q199 CBSE 2023
    1. (i)Differentiate ​between a solenoid ​and ​a circular coil.
    2. (ii)Explain how a solenoid can ​be made in a ​school laboratory.
    3. (iii)​Write one use of the strong ​magnetic field produced inside a current ​carrying solenoid.
    Show answer

    A solenoid is a close cylindrical coil with a strong uniform field inside, unlike a circular coil; it is used to make electromagnets.

    (i) A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder, whereas a circular coil is one or more circular turns of wire lying in one plane. The field inside a solenoid is strong, uniform and parallel to its axis, and outside it the solenoid behaves like a bar magnet with a north and a south pole; a circular coil produces a field that is not uniform: its lines are circles near the wire and nearly straight, perpendicular to the coil, at its centre, and along its axis the field falls away quickly with distance. (ii) Take a long insulated copper wire and wind it closely, turn beside turn and all in the same sense, in the form of a helix on a cylindrical non-conducting former such as a glass or plastic tube or a cardboard roll, leaving two free ends. Scrape the insulation from these ends and connect them through a plug key to a battery. When the key is closed a current flows through the turns and the arrangement acts as a solenoid. (iii) The strong magnetic field inside a current carrying solenoid is used to magnetise a piece of soft iron placed inside it, that is, to make an electromagnet, which is used in electric bells, loudspeakers and cranes for lifting iron.

    Step-by-step solution →
20. Q200 CBSE 2023
    (i) ​Draw the pattern of magnetic field lines of

    1. (1)a ​current carrying solenoid
    2. (2)a bar magnet (ii) List ​two ​distinguishing ​features between the ​two ​fields.
    Show answer

    A solenoid's field is temporary, controllable and reversible; a bar magnet's field is permanent, fixed and not reversible.

    (i) (1) Solenoid: the field lines inside the coil are straight, parallel and evenly spaced, running along the axis from one end to the other, which shows that the field inside is uniform; outside, they come out of one end, curve round the coil and go in at the other end, forming closed loops. The end the lines come out of is the north pole and the end they enter is the south pole. (2) Bar magnet: the field lines come out of the north pole, curve round outside the magnet and enter the south pole, continuing inside the magnet from south to north so that every line is a closed loop. They are crowded near the poles, where the field is strong, and far apart away from the magnet, where it is weak. No two field lines cross. (ii) Two distinguishing features: 1. The magnetic field of a solenoid is temporary and can be controlled - it lasts only while the current flows, and its strength can be increased by increasing the current, increasing the number of turns, or inserting a soft-iron core - whereas the field of a bar magnet is permanent and its strength is fixed. 2. The polarity of a solenoid can be reversed by reversing the direction of the current in it, whereas the polarity of a bar magnet cannot be reversed.

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