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 7 of 14

1. Q121 CBSE 2025
   The given figure shows the current passing through ​the ​straight conductor XY.

   1. (i)Copy the diagram and draw the ​magnetic field lines when current flows from conductor X to Y.
   2. (ii)Name and state the rule used in determining the direction of the magnetic field lines ​in the situation given above.
   3. (iii)State Fleming’s left hand ​rule. Using this rule, determine ​the direction of force applied on an electron entering a uniform magnetic field as shown in the figure.

   Show answer

   Field lines are clockwise circles (seen from above) by the right-hand thumb rule; the force on the electron is out of the paper.

   (i) The magnetic field lines are concentric circles centred on the conductor and lying in the plane of the cardboard sheet, that is at right angles to XY; they are close together near the wire and farther apart away from it. With the current flowing from X to Y (downwards) the circles run clockwise when seen from above. (ii) The rule is the right-hand thumb rule (Maxwell's corkscrew rule): if a current carrying straight conductor is held in the right hand with the thumb pointing in the direction of the current, then the fingers wrapped round the conductor give the direction of the magnetic field lines. (iii) Fleming's left hand rule: stretch the thumb, forefinger and central finger of the left hand mutually perpendicular; if the forefinger points along the magnetic field and the central finger along the current, the thumb gives the direction of the force. Here the electron moves upwards, so the conventional current is downwards, and the field is towards the right; the thumb then points out of the plane of the paper, so the force on the electron is directed perpendicular to the paper, outwards, towards the reader.

   Step-by-step solution →
2. Q122 CBSE 2025
   (i) Draw the pattern of the magnetic field lines for the two parallel straight conductors carrying current of same ​magnitude 'I' in opposite directions as shown. Show the direction of magnetic field at a point O which is equidistant from the two conductors. (Consider ​that the conductors are inserted normal to the plane of a rectangular cardboard.) (ii) In our houses we receive A.C. electric power of 220 ​V. In electric iron or electric heater cables having ​three wires with insulation of three different colours – red, black and green are used ​to ​draw current from the mains.

   1. (a)What are these three different wires called? Name them colourwise.
   2. (b)What is the potential difference between the red wire and the black wire?
   3. (c)What is ​the role ​of the wire with green insulation in case of accidental leakage of electric current to the metallic body of an electrical appliance?

   Show answer

   (i) Circular field lines round each wire; at O both fields point out of the paper and add; (ii) live, neutral, earth; 220 V.

   (i) Round each conductor the magnetic field lines are concentric circles lying in planes perpendicular to it, crowded near the conductor and farther apart away from it. Because the currents are opposite, the two sets of circles run in opposite senses, so between the conductors both fields point the same way and add, while outside the pair they oppose. By the right-hand thumb rule, the left conductor (current downwards) gives at O, which lies to its right, a field directed out of the plane of the paper, and the right conductor (current upwards) gives at O, which lies to its left, a field also directed out of the plane of the paper. The magnetic field at O is therefore perpendicular to the plane of the paper and directed **outwards**, towards the reader, and since O is equidistant from the two equal currents its magnitude is twice the field of either conductor alone. Put in a way that does not depend on how the figure is viewed: the field at O is perpendicular both to the currents and to the line joining the two conductors, so on a rectangular cardboard held normal to the conductors it lies in that card, at right angles to the line joining them. (ii)(a) Red is the live wire, black is the neutral wire and green is the earth wire. (b) The potential difference between the red (live) wire and the black (neutral) wire is $220$ V, because the neutral wire is at the potential of the earth. (c) The green earth wire is connected to a metal plate buried deep in the earth and so provides a low-resistance path to the ground for the metallic body of the appliance. If current leaks on to that body the earth wire carries it away to the earth, keeping the body at the earth's potential so that a person touching the appliance does not get a severe shock, and the large current that flows blows the fuse.

   Step-by-step solution →
3. Q123 CBSE 2025
   What are magnetic field lines ? How is the ​direction of magnetic field at a point determined ​? Draw the pattern of magnetic field lines of the magnetic field produced by a current carrying ​circular loop. Mark on it the direction of

   1. (i)current and
   2. (ii)magnetic field ​lines. Name ​the two ​factors on which the magnitude of the magnetic field due to a ​current carrying coil depends.
   Show answer

   Field lines are paths of a free north pole; a compass shows their direction; a coil's field depends on its current and turns.

   Magnetic field lines are the paths along which a free north magnetic pole would move in a magnetic field; equivalently, the tangent to a field line at any point gives the direction of the magnetic field at that point. They are closed continuous curves, run from north to south outside a magnet, never cross one another, and are crowded where the field is strong. The direction of the field at a point is found by placing a small compass needle there: the direction in which its north end points is the direction of the field; for a current-carrying conductor the right-hand thumb rule gives the same direction, the thumb along the current and the curled fingers along the field lines. For a circular loop the field lines are closed curves encircling the wire, growing larger with distance from it, and at the centre of the loop they appear as a straight line along the axis, perpendicular to the plane of the loop. On the diagram the current is marked by a dot for current out of the page and a cross for current into the page, and the arrowheads on the field lines run up through the middle of the loop, outwards beyond it and round the wire. The magnitude of the magnetic field of a current-carrying coil depends on (1) the strength of the current through it, $B\propto I$, and (2) the number of turns of the coil, $B\propto n$; it is also inversely proportional to the radius of the coil.

   Step-by-step solution →
4. Q124 CBSE 2025
   (a) Study the following electric circuit diagram and answer the questions that follow :

   1. (i)What does the ​circuit diagram shows ?
   2. (ii)​What will happen if ​the direction of current is reversed ? Justify your answer giving ​circuit ​diagram. (b) Name and state the rule to determine ​the direction of magnetic field associated with a ​straight current carrying conductor.

   Show answer

   Current produces a magnetic field, deflecting the compass needle; reversing the current reverses the deflection; the right-hand thumb rule gives the field direction.

   (a) (i) The circuit shows that an electric current flowing through a conductor produces a magnetic field around it. When the key is closed, current flows from north to south in the straight wire laid over the compass, and the north end of the compass needle is deflected towards the East. (ii) If the direction of current is reversed, by reversing the connections of the cells, the current flows from south to north in the wire and the needle is deflected the opposite way, towards the West. The direction of the magnetic field produced by a current depends on the direction of the current, so reversing the current reverses the field. In the circuit diagram the cells are turned round, so every current arrow points the other way. (b) The right-hand thumb rule: imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current; then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field.

   Step-by-step solution →
5. Q125 CBSE 2025
   (i) Define the ​term solenoid. ​Draw the pattern of the magnetic field lines in and around a current carrying straight solenoid. Mark on the pattern ​the ​

   1. (i)direction of current,
   2. (ii)direction of field lines near ​the ends of the solenoid, and
   3. (iii)region where ​the magnetic field is uniform. (ii) ​How would you make an electromagnet ​using a current carrying solenoid ?
   Show answer

   A solenoid is a closely wound coil with a bar-magnet-like field, uniform inside; a soft iron core inside it, with current, makes an electromagnet.

   (i) A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. Its magnetic field pattern is like that of a bar magnet: inside the solenoid the field lines are straight, parallel and equally spaced, running from the south end to the north end, while outside they emerge from the north end, curve round and enter at the south end, forming closed loops that never cross. On the pattern, mark (i) the direction of the current with arrows on the turns and the leads, (ii) the field lines coming out at the end that is the north pole and going in at the end that is the south pole, and (iii) the central region inside the coil, where the equally spaced parallel lines show that the field is uniform. (ii) To make an electromagnet, place a rod of soft iron inside the solenoid and pass a current through the coil. The soft iron is strongly magnetised and the arrangement acts as a powerful magnet as long as the current flows; the strength can be increased by increasing the current or the number of turns, and the magnetism is lost when the current is switched off.

   Step-by-step solution →
6. Q126 CBSE 2025
   (i) By using the ​given experimental set-up. How can it be shown that :

   1. (a)​a force is exerted on the current-carrying conductor AB when it is placed in a magnetic field.
   2. (b)the direction of ​force can be ​reversed ​in ​two ways. (ii) ​When will the magnitude of the force be highest? (iii) State ​Fleming's left hand rule.

   Show answer

   A current-carrying rod in a magnetic field is displaced; reversing current or field reverses the force; it is greatest when they are perpendicular.

   (i)(a) Complete the circuit and insert the key K. Current flows through the suspended rod AB, which lies between the poles of the horseshoe magnet, and the rod is at once displaced sideways (towards the left in the given figure); on removing the key it returns to rest. Since the freely hung rod moves only while current flows, a force must act on a current-carrying conductor placed in a magnetic field. (i)(b) The direction of that force is reversed in two ways: first, by reversing the direction of the current through AB, that is by interchanging the terminals of the battery while leaving the magnet as it is; second, by reversing the direction of the magnetic field, that is by interchanging the poles of the horseshoe magnet while leaving the current as it is. In each case the rod is displaced the opposite way. (Doing both together leaves the direction unchanged.) (ii) The magnitude of the force is highest when the direction of the current is perpendicular to the direction of the magnetic field, since $F=BIL\sin \theta$ is greatest at $\theta =90^{\circ }$. (iii) Fleming's left hand rule: stretch the thumb, forefinger and centre finger of the **left** hand so that they are mutually perpendicular; if the forefinger points along the magnetic field and the centre finger along the current, then the thumb points along the direction of the force, that is of the motion, of the conductor.

   Step-by-step solution →
7. Q127 CBSE 2025
   Why can't two magnetic field lines cross ​each other ? Draw magnetic field lines showing the direction of the magnetic field due to a current carrying ​long straight solenoid. State ​the conclusion which can be ​drawn from the pattern of magnetic field lines inside the solenoid. Name any two factors on ​which the magnitude of ​the magnetic ​field due to this solenoid ​depends.
   Show answer

   Field lines cannot cross because the field has one direction at a point; inside a solenoid it is uniform.

   Two magnetic field lines cannot cross because, if they did, two tangents could be drawn at the point of crossing, so the magnetic field there would have two directions at the same time. A compass needle placed at that point can come to rest in one direction only, so the field at a point has a single direction and no crossing is possible. For a long straight current-carrying solenoid the field lines are straight, parallel and equally spaced inside the coil, running along its axis; at the ends they emerge, spread out, curve round outside and re-enter at the other end, each line being a closed curve. The end from which the lines emerge is the north pole and the end at which they enter is the south pole, so outside the solenoid the lines run from north to south, just as for a bar magnet. The conclusion from the pattern inside is that the magnetic field inside a current-carrying solenoid is uniform, that is, it has the same magnitude and the same direction at every point there. The magnitude of the field depends on (1) the strength of the current through the solenoid and (2) the number of turns per unit length of the solenoid, and also on the nature of the core, a soft iron core increasing it greatly.

   Step-by-step solution →
8. Q128 CBSE 2025
   (a) ​Draw the ​pattern of magnetic field lines of

   1. (i)a ​bar magnet
   2. (ii)​a current carrying solenoid List two distinguishing features between the two magnetic fields. (b) Study the following three diagrams in which the entry ​of ​an electron in a magnetic field is shown. Identify the case in which the magnetic force experienced by the electron is (i) maximum, ​and (ii) minimum. Give reason for your answers in each case.

   Show answer

   Bar-magnet and solenoid field patterns, the solenoid's being uniform inside; the electron feels maximum force in (A) and minimum in (C).

   (a) (i) Bar magnet: closed field lines that emerge from the north pole, curve round outside and enter the south pole, running from S to N inside the magnet; they never cross and are crowded near the poles. (ii) Current-carrying solenoid: parallel, equally spaced straight lines inside, along the axis; outside, a pattern like that of a bar magnet, one end acting as a north pole and the other as a south pole. Two distinguishing features: (1) Inside a solenoid the field is uniform — its field lines are parallel and equally spaced — whereas the field lines around a bar magnet curve and crowd together near the poles, so that field is non-uniform. (2) A solenoid’s field exists only while current flows, and its strength and direction can be changed by changing or reversing the current (or by changing the number of turns); a bar magnet’s field is permanent and fixed. (b) (i) Maximum force in (A): the electron moves at right angles to the magnetic field. (ii) Minimum force in (C): the electron moves along the field lines, opposite to the field, so it experiences no magnetic force at all. The force on a moving charge, as on a current, is greatest when its motion is perpendicular to the field and zero when it is parallel or opposite to the field; in (B) it moves at an angle, so the force lies in between.

   Step-by-step solution →
9. Q129 CBSE 2025
   In ​our homes, we receive the supply of electric power through a ​main supply also called mains, either supported ​through overhead electric poles or by underground cables. In our country the ​potential difference between ​the two wires (live wire and neutral ​wire) of this supply ​is 220 V.

   1. (a)Write the colours of the insulation covers of the line wires through which supply comes to our homes.[1]
   2. (b)What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated ?[1]
   3. (c)(i)What is the function of the earth wire ? State the advantage of the earth wire in domestic electric appliances such as electric iron.[2]
   4. (c)(ii)OR : List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.[2]
   Show answer

   Live wire is red, neutral black; the iron needs a 5 A circuit ($I\approx 4.55$ A); the earth wire carries leakage current to the earth.

   (a) The live wire has a red insulation cover and the neutral wire a black insulation cover. (The earth wire is green, but it is not one of the two wires through which the supply comes.) (b) $I=P/V=1000/220\approx 4.55$ A, so the circuit must be able to carry at least this much: the standard $5$ A domestic circuit is required. (c)(i) The earth wire is connected to a metal plate buried deep in the earth and provides a low-resistance conducting path for the current to the earth. Its advantage is that the metal body of an appliance such as an electric iron is joined to it, so if the live wire touches the body the leakage current runs to the earth instead of through the user, the body stays at earth potential and the user escapes a severe shock (the large current also blows the fuse). (c)(ii) Two precautions: use a fuse of the correct rating in every circuit, which melts and breaks the circuit when overloading or a short circuit makes the current rise abruptly, so the appliance and the wiring are not damaged; and avoid connecting too many appliances to one socket and keep the insulation in good repair, so the current never exceeds what the wiring is rated for and the live and neutral wires cannot touch.

   Step-by-step solution →
10. Q130 CBSE 2025
    In order ​to obtain ​magnetic field ​lines around a bar magnet, a student performed an experiment using a magnetic ​compass and a bar magnet. The magnet ​was ​placed on a sheet ​of white paper fixed on a drawing board. ​Using magnetic needle he obtained on the paper a pattern of magnetic field lines (as shown below) around the bar magnet.

    1. (a)By convention, the field lines emerge from north pole and merge at south pole. Why ? Give reason.[1]
    2. (b)State the relationship between strength of the magnetic field and the degree of closeness of the field lines.[1]
    3. (c)(i)(i) No two field lines can ever intersect each other. Give reason. (ii) The magnetic field in a given region is uniform. Draw a diagram to represent it.[2]
    4. (c)(ii)OR : Draw the pattern of the magnetic field lines through and around a current carrying solenoid. What does the pattern of field lines inside the solenoid represent ?[2]
    Show answer

    Lines emerge from N and merge at S; closer lines mean a stronger field; lines never cross; the field inside a solenoid is uniform.

    (a) The direction of a magnetic field line at a point is the direction in which the north pole of a small compass needle placed there comes to rest, that is, the direction of the force on a free north pole. Outside the magnet such a free north pole is repelled by the north pole of the magnet and attracted by its south pole, so it moves away from the north pole and towards the south pole. The line it traces is therefore drawn emerging from the north pole and merging at the south pole. (Inside the magnet the direction is from south to north, so every field line is a closed curve.) (b) The strength of the magnetic field is directly related to the closeness of the field lines: the more closely the lines are spaced, the stronger the field, and the farther apart they are, the weaker the field. The degree of closeness - the number of field lines crossing unit area held at right angles to them - represents the relative strength of the field. (c)(i) (i) If two field lines intersected, the magnetic field at the point of intersection would have two directions at the same time, so a compass needle placed there would have to point in two directions at once. That is impossible, so no two field lines can ever intersect. (ii) A uniform magnetic field is represented by straight field lines that are parallel to one another, equally spaced, and all pointing in the same direction (see the diagram). (c)(ii) Outside a current-carrying solenoid the field lines emerge from one end, which behaves as a north pole, loop round and enter the other end, which behaves as a south pole, exactly as they do for a bar magnet; inside the solenoid they run straight along the axis, parallel to one another and equally spaced (see the diagram). That pattern inside represents a uniform magnetic field: the magnetic field is the same, in magnitude and in direction, at all points inside the solenoid.

    Step-by-step solution →
11. Q131 CBSE 2024
    The direction of magnetic field ​produced ​around ​a current ​carrying ​straight conductor is determined ​by using :

    1. (a)Fleming’s left hand rule
    2. (b)Left hand thumb rule
    3. (c)Right hand thumb rule
    4. (d)Fleming’s right hand rule
    Show answer

    (c) Right hand thumb rule

    Step-by-step solution →
12. Q132 CBSE 2024
    When a steady current flows through a long straight solenoid ​it behaves ​as a bar magnet having a north ​and a south pole. ​The strength of ​the magnetic ​field inside the ​solenoid is :

    1. (a)zero everywhere.
    2. (b)uniform everywhere.
    3. (c)maximum at the ends and minimum at the centre.
    4. (d)minimum at the ends and maximum at the centre.
    Show answer

    (b) uniform everywhere.

    Step-by-step solution →
13. Q133 CBSE 2024
    The ​pattern ​of the magnetic field produced ​inside a current carrying ​solenoid ​is ​:

    1. (a)Four parallel, equally spaced straight lines, each with an arrowhead pointing the same way (to the right).
    2. (b)Three concentric closed loops round a central dot, with arrowheads showing a clockwise sense.
    3. (c)The same four parallel straight lines with arrowheads to the right, plus a curved line above them and a curved line below them whose arrowheads also point to the right.
    4. (d)Two small circles with dots at their centres, above and below a straight central line; curved lines between them bend towards the central line, with arrowheads pointing to the left.
    Show answer

    (a) Four parallel, equally spaced straight lines, each with an arrowhead pointing the same way (to the right).

    Step-by-step solution →
14. Q134 CBSE 2024
    The ​current carrying device ​which produces a ​magnetic field similar to that of ​a ​bar magnet is :

    1. (a)A straight conductor
    2. (b)A circular loop
    3. (c)A solenoid
    4. (d)A circular coil
    Show answer

    (c) A solenoid

    Step-by-step solution →
15. Q135 CBSE 2024
    When we ​connect too many ​electrical appliances to a ​single socket in a circuit ​having a fixed ​value of ​current rating ​:

    1. (a)the total resistance of the circuit increases.
    2. (b)the current drawn from the source decreases.
    3. (c)the current increases beyond the rated value.
    4. (d)each appliance starts drawing more and more current from the source.
    Show answer

    (c) the current increases beyond the rated value.

    Step-by-step solution →
16. Q136 CBSE 2024
    When too many ​electrical appliances ​are connected ​to a ​single socket ​in a ​domestic ​circuit :

    1. (a)total resistance of the circuit increases.
    2. (b)current in the circuit decreases.
    3. (c)short circuiting occurs.
    4. (d)current in the circuit increases.
    Show answer

    (d) current in the circuit increases.

    Step-by-step solution →
17. Q137 CBSE 2024
    A ​rectangular loop ​ABCD carrying a ​current $I$ is situated ​near a straight conductor XY, such that the ​conductor is parallel to the side AB of the loop and is in the plane of the loop. ​If a steady current $I$ is established in ​the conductor as shown, the conductor XY will

    1. (a)remain stationary.
    2. (b)move towards the side AB of the loop.
    3. (c)move away from the side AB of the loop.
    4. (d)rotate about its axis.
    Show answer

    (b) move towards the side AB of the loop.

    Step-by-step solution →
18. Q138 CBSE 2024
    A ​uniform ​magnetic field exists ​in the plane ​of paper ​as shown ​in the ​diagram. ​In this field, an electron ($e^{-}$) and a positron ($p^{+}$) enter as shown. The electron and positron experience forces :

    1. (a)both pointing into the plane of the paper.
    2. (b)both pointing out of the plane of the paper.
    3. (c)pointing into the plane of the paper and out of the plane of the paper respectively.
    4. (d)pointing out of the plane of the paper and into the plane of the paper respectively.
    Show answer

    (a) both pointing into the plane of the paper.

    Step-by-step solution →
19. Q139 CBSE 2024
    Strength of magnetic field produced by a ​current ​carrying solenoid DOES ​NOT depend ​upon ​:

    1. (a)number of turns in the solenoid
    2. (b)direction of the current flowing through it
    3. (c)radius of solenoid
    4. (d)material of core of the solenoid
    Show answer

    (b) direction of the current flowing through it

    Step-by-step solution →
20. Q140 CBSE 2024
    Study the following statements :

    1. (a)A ​fuse in a circuit prevents damage to the circuit due to overloading.
    2. (b)Total resistance ​in a ​circuit increases due to overloading.
    3. (c)During ​short circuiting ​the current in the ​circuit abruptly increases.
    4. (d)In order that each appliance has same current, they are connected in parallel to ​each other. The correct statements are

    1. (a)(a) and (b)
    2. (b)(b) and (d)
    3. (c)(a) and (c)
    4. (d)(a), (c) and (d)
    Show answer

    (c) (a) and (c)

    Step-by-step solution →