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.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 1 of 9

1. Q1 NCERT · Exercises
   Which of the ​following ​correctly ​describes the magnetic field ​near ​a long straight ​wire?

   1. (a)The field consists of straight lines perpendicular to the wire.
   2. (b)The field consists of straight lines parallel to the wire.
   3. (c)The field consists of radial lines originating from the wire.
   4. (d)The field consists of concentric circles centred on the wire.
   Show answer

   (d) The field consists of concentric circles centred on the wire.

   Step-by-step solution →
2. Q2 NCERT · Intext Questions (Page 196)
   Why ​does ​a ​compass needle get ​deflected when ​brought ​near a ​bar ​magnet?
   Show answer

   The needle is a small magnet, so the bar magnet's field exerts opposite forces on its poles and turns it along the field.

   A compass needle is itself a small bar magnet with a north pole and a south pole. A bar magnet has a magnetic field in the space around it, so when the compass is brought near, the field exerts a force on each pole of the needle — the needle's north pole is repelled by the magnet's north pole and attracted by its south pole, and the needle's south pole is acted on the opposite way. These two opposite forces act at the two ends of the pivoted needle and so turn it. The needle is deflected from its usual north–south position and comes to rest pointing along the direction of the magnetic field at that place.

   Step-by-step solution →
3. Q3 NCERT · Exercises
   At the ​time of ​short circuit, the ​current ​in ​the circuit

   1. (a)reduces substantially.
   2. (b)does not change.
   3. (c)increases heavily.
   4. (d)vary continuously.
   Show answer

   (c) increases heavily.

   Step-by-step solution →
4. Q4 NCERT · Exercises
   State whether the following statements are true or false.

   1. (a)The field at the ​centre ​of a long circular coil carrying current ​will be parallel straight ​lines. ​
   2. (b)A wire with a green insulation is usually the live wire of ​an electric ​supply.
   Show answer

   (a) True: the field inside a long coil is uniform. (b) False: green insulation marks the earth wire, not the live wire.

   (a) True. A long circular coil carrying a current is a solenoid, and inside a long solenoid the magnetic field lines are straight, parallel and equally spaced — which means the field there has the same magnitude and direction at every point, that is, it is uniform. (b) False. Green, or green with a yellow stripe, is the colour of the **earth** wire, which runs from the metal body of an appliance to a plate buried in the ground and carries no current in normal working. The live wire is red, or brown in newer wiring.

   Step-by-step solution →
5. Q5 NCERT · Exercises
   List ​two methods of ​producing magnetic ​fields.
   Show answer

   A permanent magnet and an electric current in a conductor each produce a magnetic field.

   Two methods are: (i) By using a permanent magnet. A bar magnet or a horseshoe magnet sets up a magnetic field in the space around it; outside the magnet the field lines run from its north pole to its south pole, and the field cannot be switched off. (ii) By passing an electric current through a conductor. A current-carrying straight wire, a circular loop or a solenoid each produces a magnetic field around it — this is Oersted’s magnetic effect of a current. A solenoid wound on a soft-iron core makes an electromagnet, whose field is strong and can be switched on and off with the current.

   Step-by-step solution →
6. Q6 NCERT · Exercises
   When ​is the force ​experienced by ​a ​current–carrying ​conductor placed in ​a magnetic ​field largest?
   Show answer

   The force is largest when the current is at right angles to the field ($\theta =90^{\circ }$), where $F=BIL$.

   The force is largest when the current-carrying conductor is placed at right angles to the magnetic field — that is, when the direction of the current is perpendicular ($90^{\circ }$) to the direction of the field. The magnitude of the force is $F=BIL\sin \theta$, where $\theta$ is the angle between the current and the field, so $F$ takes its greatest value $F=BIL$ when $\sin \theta =1$, at $\theta =90^{\circ }$. When the conductor lies along the field, $\theta =0^{\circ }$ and the force is zero.

   Step-by-step solution →
7. Q7 NCERT · Exercises
   Imagine that you are sitting in ​a chamber with your back to one wall. An electron beam, moving ​horizontally ​from back wall towards the front wall, is ​deflected by a ​strong magnetic field to your ​right ​side. What is the direction of magnetic field?
   Show answer

   The field is vertically downwards, found by Fleming's left-hand rule with the current taken opposite to the electron beam.

   The magnetic field is directed vertically downwards. The beam is made of electrons, which are negative, so the conventional current runs opposite to the beam — from the front wall back towards you. The force on the beam is to your right and is at right angles to that current, and the field must be at right angles to both, so the field can only be vertical. Applying Fleming’s left-hand rule with the middle finger pointing towards you (the current) and the thumb pointing to your right (the force), the first finger — the field — points straight down.

   Step-by-step solution →
8. Q8 NCERT · Exercises
   State ​the rule to determine the direction of a

   1. (i)magnetic ​field produced around ​a straight conductor-carrying current,
   2. (ii)force experienced by a current-carrying straight conductor placed in a magnetic field which ​is perpendicular to it, and ​
   3. (iii)current ​induced in ​a coil due to its ​rotation in a magnetic field.
   Show answer

   The right-hand thumb rule gives the field, Fleming’s left-hand rule the force, and Fleming’s right-hand rule the induced current.

   (i) Right-hand thumb rule (also called Maxwell’s corkscrew rule). Hold the straight current-carrying conductor in your right hand so that the thumb points along the direction of the conventional current; the fingers wrapped around the conductor then give the direction of the magnetic field lines. (ii) 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. (iii) Fleming’s right-hand rule. Stretch the thumb, the forefinger and the middle finger of the right hand so that they are mutually perpendicular; if the forefinger points along the magnetic field and the thumb along the direction of motion of the conductor, the middle finger points in the direction of the induced current.

   Step-by-step solution →
9. Q9 NCERT · Exercises
   When does ​an electric ​short ​circuit occur?
   Show answer

   A short circuit occurs when the live wire and the neutral wire come into direct contact.

   An electric short circuit occurs when the live wire and the neutral wire come into direct contact with each other. This happens when the insulation of the wires is damaged or worn through, when there is a fault inside an appliance, or at a loose connection. The current then bypasses the appliance and returns to the supply through a path whose resistance is only a fraction of an ohm. Since the supply voltage stays at about $220$ V, by $I=V/R$ the current rises heavily — from a few amperes to hundreds of amperes — and the heat produced, $H=I^{2}Rt$, can melt the wires and start a fire. The fuse in the live wire melts first and breaks the circuit.

   Step-by-step solution →
10. Q10 NCERT · Exercises
    What is ​the function of an ​earth ​wire? ​Why is it ​necessary to ​earth ​metallic appliances?
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    The earth wire gives a low-resistance path to the ground, keeping the metal body at earth potential and carrying away fault current.

    Function of the earth wire: The earth wire is the green (or green-and-yellow) wire of a domestic supply. It is connected at one end to the metallic body of the appliance and at the other to a metal plate buried deep in the ground near the house, and it provides a low-resistance conducting path from the body to the earth. In normal working it carries no current; its job is to hold the metal body at the potential of the earth, which is taken as $0$ V, and to carry away any current that reaches the body during a fault. Why metallic appliances must be earthed: If the insulation inside a metal-bodied appliance fails and the live wire touches the casing, the casing is raised to about $220$ V. Anyone who then touches it completes a path to the ground through their own body and receives a severe, possibly fatal, electric shock. With the body earthed, the fault current instead flows through the earth wire, whose resistance is a fraction of an ohm against the thousands of ohms of a human body, so almost none of it passes through the person and the casing never rises above the earth’s potential. The large fault current also melts the fuse in the live wire and disconnects the supply. This is why metallic appliances such as an electric iron, a toaster or a refrigerator must always be earthed.

    Step-by-step solution →
11. Q11 NCERT · Intext Questions (Page 200)
    Draw magnetic field ​lines ​around ​a ​bar ​magnet.
    Show answer

    Closed lines run from north to south outside the magnet and south to north inside, crowded near the poles, with arrowheads and no crossings.

    The field lines are closed curves. Outside the magnet they emerge from the north pole, curve round through the space on either side and enter the magnet at the south pole; inside the magnet each line continues from the south pole to the north pole, so it closes on itself. Every line carries an arrowhead showing this direction. The lines are crowded together near the two poles, where the field is strongest, and are widely spaced near the middle of the sides, where it is weakest, and no two of them ever cross. The figure shows the completed drawing.

    Step-by-step solution →
12. Q12 NCERT · Intext Questions (Page 200)
    List the ​properties ​of magnetic ​field ​lines.
    Show answer

    Field lines show the field direction, run north to south outside a magnet, are closed curves, show strength by their closeness and never cross.

    The properties of magnetic field lines are: (i) A field line is the path along which a free north pole would tend to move, and the direction of the field at a point is the tangent to the line there — the direction the north pole of a compass needle placed there would take. (ii) Outside a magnet the lines run from the north pole to the south pole, and inside the magnet from the south pole to the north pole, so every field line is a closed continuous curve with no beginning and no end. (iii) The lines are crowded together where the field is strong and are spread apart where it is weak, so their relative closeness shows the relative strength of the field. (iv) No two field lines ever intersect, because at the crossing point the field would have two directions and a compass needle cannot point two ways at once.

    Step-by-step solution →
13. Q13 NCERT · Intext Questions (Page 200)
    Why ​don’t ​two magnetic field lines ​intersect ​each ​other?
    Show answer

    At a crossing point the field would have two directions at once, which is impossible, so field lines never intersect.

    The tangent to a magnetic field line at any point gives the direction of the magnetic field at that point. If two field lines crossed at a point P, there would be two different tangents at P, so the magnetic field at P would have two different directions at the same time, and a compass needle placed at P would have to point in two directions at once. That is impossible, because the field at a point has one definite direction. Hence two magnetic field lines never intersect each other.

    Step-by-step solution →
14. Q14 NCERT · Intext Questions (Page 201)
    Consider a circular ​loop of wire ​lying in the plane of ​the table. Let ​the current pass through the loop clockwise. Apply the ​right-hand rule to find ​out ​the direction of the magnetic field inside ​and outside the loop.
    Show answer

    Inside the loop the field is downwards, into the table; outside it is upwards, out of the table.

    Inside the loop the magnetic field is directed vertically downwards, that is into the table, at right angles to the plane of the loop. Outside the loop the field is directed vertically upwards, out of the table. Curling the fingers of the right hand along the clockwise current gives a thumb pointing down through the loop, and because field lines are closed curves the lines that go down through the loop return upwards all around the outside. The upper face of the loop therefore behaves as a south pole and the lower face as a north pole.

    Step-by-step solution →
15. Q15 NCERT · Intext Questions (Page 201)
    The ​magnetic ​field in a given region is ​uniform. ​Draw a diagram ​to represent it.
    Show answer

    A uniform field is drawn as straight, parallel, equally spaced lines with arrowheads all in the same direction.

    A uniform magnetic field is represented by straight, parallel field lines that are equally spaced and all carry arrowheads pointing the same way, drawn right across the region. The parallel arrows say that the direction is the same at every point, and the equal spacing says that the magnitude is the same at every point. If the field is at right angles to the plane of the paper it is drawn instead as an evenly spaced array of crosses (field going into the page) or of dots (field coming out of the page). The field inside a long current-carrying solenoid is the standard example. The figure shows both forms of the diagram.

    Step-by-step solution →
16. Q16 NCERT · Intext Questions (Page 201)
    Choose the correct option. The ​magnetic ​field ​inside ​a long ​straight solenoid-carrying ​current

    1. (a)is zero.
    2. (b)decreases as we move towards its end.
    3. (c)increases as we move towards its end.
    4. (d)is the same at all points.
    Show answer

    (d) is the same at all points.

    Step-by-step solution →
17. Q17 NCERT · Intext Questions (Page 203)
    Which of the ​following ​property of ​a ​proton can ​change while it ​moves freely in a ​magnetic field? (There may be more than one correct answer.)

    1. (a)mass
    2. (b)speed
    3. (c)velocity
    4. (d)momentum
    Show answer

    (c) velocity

    (d) momentum

    Step-by-step solution →
18. Q18 NCERT · Intext Questions (Page 203)
    In ​Activity 12.7, how do we think ​the displacement of rod AB will ​be affected if

    1. (i)​current in rod AB is increased;
    2. (ii)a stronger horse-shoe magnet is used; and
    3. (iii)length ​of the ​rod AB is increased?
    Show answer

    In all three cases the displacement of rod AB increases, since the force $F=BIL$ increases.

    In all three cases the displacement of the rod AB increases. (i) Increasing the current in AB increases the force on it, because the force on a current-carrying conductor grows with the current, so the rod is displaced further. (ii) A stronger horse-shoe magnet gives a stronger magnetic field between its poles, which again makes the force larger and the displacement greater. (iii) A longer rod places a greater length of current-carrying conductor inside the field, so more of it is pushed, the force is larger and the displacement increases. Taking the three together, $F=BIL$, and each change increases one factor while leaving the other two alone. The direction of the displacement does not change in any case: it is still towards the left, because Fleming's left-hand rule depends on the directions of the current and the field, and neither has been reversed.

    Step-by-step solution →
19. Q19 NCERT · Intext Questions (Page 203)
    A positively-charged particle (alpha-particle) ​projected ​towards ​west is deflected ​towards north ​by a magnetic ​field. ​The direction of magnetic field is

    1. (a)towards south
    2. (b)towards east
    3. (c)downward
    4. (d)upward
    Show answer

    (d) upward

    Step-by-step solution →
20. Q20 NCERT · Intext Questions (Page 205)
    Name ​two ​safety ​measures commonly used ​in electric ​circuits and ​appliances.
    Show answer

    Two safety measures are a fuse of proper rating in the live wire and earthing of metal-bodied appliances.

    Two safety measures are: (i) An electric fuse of a proper rating, connected in series with the live wire of each circuit. When the current exceeds the safe value because of overloading or a short circuit, the Joule heating in the fuse melts it and breaks the circuit, protecting the wiring and the appliances. (ii) Earthing of appliances that have a metallic body: the body is joined by the green earth wire to a metal plate buried deep in the earth, which provides a low-resistance path for any leakage current and keeps the body at earth potential, so that the user does not receive a severe electric shock.

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