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 8 of 14

1. Q141 CBSE 2024
   For ​Questions ​number 17 and 20, two ​statements are given — one labelled as Assertion ​(A) ​and the ​other labelled as Reason (R). Select the correct answer ​to these questions from the ​codes (a), (b), (c) and (d) as given below.

   Assertion (A): The intensity of the magnetic field produced at the centre of a current carrying circular coil increases on increasing the number of turns in the coil.

   Reason (R): The current that flows in each turn of the coil has the same magnitude and same direction and the magnetic field, due to each turn, just adds up.

   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 and Reason (R) is false.
   4. (d)Assertion (A) is false and 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 →
2. Q142 CBSE 2024
   Two statements are given — one labelled Assertion ​(A) and the ​other labelled Reason ​(R). ​Select the correct ​answer from ​the codes (a), ​(b), ​(c) and (d) as given below.

   Assertion (A): Magnetic field lines never intersect each other.

   Reason (R): If two field lines intersect each other at a point then it would mean that at the point of intersection the resultant field has two directions, which is not possible.

   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 →
3. Q143 CBSE 2024
   For Questions number 17 to 20, two statements are given ​— one labelled as Assertion (A) and ​the ​other labelled as ​Reason (R). Select the correct answer to these questions ​from the codes (a), ​(b), (c) and (d) ​as given ​below.

   Assertion (A): Magnetic field lines never intersect each other.

   Reason (R): If they intersect, then at the point of intersection, the compass needle would point towards two directions, which is not possible.

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

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

   Step-by-step solution →
4. Q144 CBSE 2024
   These ​questions consist ​of two statements ​– ​Assertion (A) and Reason (R). ​Answer these questions selecting the ​appropriate ​option given ​below :

   Assertion (A): The deflection of a compass needle placed near a current carrying wire decreases when the magnitude of an electric current in the wire is increased.

   Reason (R): Strength of the magnetic field at a point due to a current carrying conductor increases on increasing the current in the conductor.

   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

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

   Step-by-step solution →
5. Q145 CBSE 2024
   Write the shape of the magnetic field ​produced ​by a current ​carrying straight conductor. State ​the rule ​to ​find the direction of this field.
   Show answer

   The field lines are concentric circles centred on the conductor; the direction is given by the right-hand thumb rule.

   Shape: The magnetic field lines around a current-carrying straight conductor are concentric circles with the conductor at their common centre, lying in planes perpendicular to the conductor; they are farther apart away from the wire, where the field is weaker. Rule: The right-hand thumb rule: if the conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers wrapped around the conductor give the direction of the magnetic field lines.

   Step-by-step solution →
6. Q146 CBSE 2024
   Draw the pattern ​of the magnetic field ​lines due to a straight ​current carrying ​conductor ​indicating the direction ​of current in the conductor and the direction of the corresponding magnetic field lines.
   Show answer

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

   The magnetic field lines of a straight current-carrying conductor are concentric circles centred on the conductor, in planes perpendicular to it, drawn farther apart as the distance from the wire increases. Their direction is given by the right-hand thumb rule: for a current flowing vertically upwards, the field lines run anticlockwise when seen from above, as in the drawing; if the current is reversed, they run clockwise.

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7. Q147 CBSE 2024
   Draw ​a ​labelled diagram to ​show the pattern ​of magnetic field lines produced ​due to a current carrying straight conductor. Mark on it ​the direction of current in ​the conductor and the direction of ​magnetic field lines.
   Show answer

   The field lines are concentric circles round the wire, anticlockwise as seen from above for an upward current.

   Diagram (see the figure): a straight conductor passes vertically through a horizontal cardboard sheet, with the current $I$ flowing upwards, marked by an arrow. The magnetic field lines are concentric circles on the card with the conductor at their centre; by the right-hand thumb rule they run anticlockwise when seen from above, marked by arrows on the circles. The circles are closer together near the wire, where the field is stronger. If the current is reversed, the field lines run clockwise.

   Step-by-step solution →
8. Q148 CBSE 2024
   Name ​the device used to ​magnetise a piece of ​magnetic ​material. Draw ​a labelled ​diagram to show the arrangement used for the magnetisation of a cylinder made of soft ​iron.
   Show answer

   A solenoid magnetises the soft iron cylinder placed inside it when current flows, forming an electromagnet.

   Device: a solenoid, a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Arrangement (see the figure): the soft iron cylinder is placed inside the solenoid, and the ends of the solenoid are connected to a battery through a key. When the key is closed, current flows through the coil and the strong magnetic field inside the solenoid magnetises the cylinder. With the current shown (flowing down the front of each turn), the left end of the cylinder becomes S and the right end N. The magnet formed is an electromagnet.

   Step-by-step solution →
9. Q149 CBSE 2024
   1. (i)Two ​magnetic ​field lines do not intersect each other. Why ?
   2. (ii)​How is a uniform magnetic field in a given region represented ​? Draw a ​diagram ​in support of ​your answer.
   Show answer

   (i) The field has only one direction at a point, so lines cannot cross; (ii) a uniform field is shown by parallel, equally spaced lines.

   (i) The direction of the magnetic field at a point is the direction in which a compass needle placed there points, and there is only one such direction. If two field lines intersected, the field at the point of intersection would have two directions, so a compass needle there would point in two directions at once, which is not possible. Hence two field lines never intersect. (ii) A uniform magnetic field is represented by parallel, straight, equally spaced field lines, all with arrows pointing in the same direction (as inside a long current-carrying solenoid). The diagram shows such parallel, equidistant lines with arrows in one direction.

   Step-by-step solution →
10. Q150 CBSE 2024
    1. (i)​How does an electric fuse prevent the circuit and the appliances from possible damage due to short circuiting or ​overloading?
    2. (ii)How is ​the type of current used in household supply different from ​the one given by dry cells or storage batteries?
    3. (iii)​For distant transmission of electric power, an alternating current (ac) is considered ​to be advantageous over direct ​current (dc). ​Why?
    Show answer

    A fuse melts to break the circuit; household supply is AC, cells give DC; AC suits long-distance transmission.

    (i) A fuse is a wire of a metal or an alloy of appropriate melting point, connected in series with the live wire. When short-circuiting or overloading makes the current rise above its rated value, the heat produced in the fuse wire ($H=I^{2}Rt$) melts it; the circuit breaks and the unduly high current stops, so the wiring and the appliances are not damaged. (ii) Household supply is alternating current (AC), which reverses its direction periodically (in India at a frequency of $50$ Hz, changing direction every $\frac{1}{100}$ s), whereas dry cells and storage batteries give direct current (DC), which always flows in one direction. (iii) AC can be transmitted over long distances without much loss of energy: its voltage can easily be stepped up for transmission, so the same power $P=VI$ is carried by a small current and the heating loss in the wires, $I^{2}R$, is small; the voltage is stepped down again before it reaches homes. The voltage of DC cannot be changed as easily.

    Step-by-step solution →
11. Q151 CBSE 2024
    (i) A straight conductor is suspended horizontally with its axis perpendicular to the magnetic field of a strong horseshoe magnet. The conductor gets displaced towards the right when a steady current is passed through it. What will happen to the displacement of the ​conductor ​if the ​:

    1. (1)Polarity of the horseshoe magnet is reversed ?
    2. (2)Direction ​of current ​in ​the conductor is reversed ?
    3. (3)Current through the conductor is ​increased ? (ii) Name and state the rule for ​determining the direction of force on a current carrying conductor placed in a magnetic field.
    Show answer

    Reversing the poles or the current moves the conductor left; a larger current moves it further right; Fleming's left-hand rule.

    (i) (1) The displacement is reversed: the conductor is now displaced towards the left, because reversing the poles reverses the magnetic field. (2) The displacement is again reversed: the conductor is displaced towards the left, because the force reverses when the current reverses. (3) The conductor is still displaced towards the right, but by a larger amount, because a larger current experiences a larger force. (ii) Fleming's left-hand rule. Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force on (motion of) the conductor.

    Step-by-step solution →
12. Q152 CBSE 2024
    Name and state the rule to ​determine the direction of a :

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

    Right-hand thumb rule gives the field direction around a straight current; Fleming's left-hand rule gives the force direction.

    (i) Right-hand thumb rule: Imagine that you are holding the current-carrying straight conductor in your right hand such that the thumb points in the direction of the current. Then the fingers wrapped around the conductor point in the direction of the field lines of the magnetic field. (ii) Fleming's left-hand rule: Stretch the thumb, forefinger and middle finger of your left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force (motion) acting on the conductor.

    Step-by-step solution →
13. Q153 CBSE 2024
    Draw a diagram to show the pattern of magnetic field lines on a horizontal sheet of paper due to a ​straight ​conductor ​passing ​through its centre and carrying current vertically upwards. Mark on it

    1. (i)the direction of current in the conductor and ​
    2. (ii)the corresponding ​magnetic field ​lines. State right hand thumb rule and ​check whether the directions marked by you are in accordance with this rule or not.
    Show answer

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

    Diagram: the field lines on the horizontal sheet are concentric circles centred on the conductor, closer together near the wire; the current is marked by an upward arrow on the conductor (out of the sheet, $\odot$, when seen from above), and the field lines are marked anticlockwise as seen from above. Right-hand thumb rule: if a current-carrying straight conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers wrap around the conductor in the direction of the magnetic field lines. Check: with the thumb pointing upwards along the current, the fingers curl anticlockwise as seen from above, which is the direction marked on the field lines. So the marked directions are in accordance with the rule.

    Step-by-step solution →
14. Q154 CBSE 2024
    1. (a)State Fleming’s left hand rule. Apply this rule to determine the direction of force experienced by a straight current carrying conductor ​AB placed ​in a uniform magnetic field as shown.
    2. (b)What will ​happen ​to an ​electron ​which enters in the same field in ​the same ​direction in which the current is flowing in the conductor AB ? Give reason to justify your answer.

    Show answer

    The force on AB is into the page; the electron is deflected, with a force out of the page, opposite to that on AB.

    (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 (motion) on the conductor. Here the field is from left to right and the current flows up the conductor from B to A, so the thumb points into the page: the force on AB is perpendicular to the plane of the page, directed into it (away from the reader). (b) The electron is deflected: it experiences a force perpendicular to both the field and its motion, directed out of the page, opposite to the force on AB. Reason: an electron is negatively charged, so an electron moving up the page is equivalent to a current flowing down the page, and for a downward current in a left-to-right field the left-hand rule gives a force out of the page.

    Step-by-step solution →
15. Q155 CBSE 2024
    Define the ​term ​solenoid. Draw the pattern of magnetic field ​lines around a current carrying solenoid. State how ​this magnetic field can be ​used to ​magnetise ​a piece of ​magnetic material, like soft iron.
    Show answer

    A solenoid is a closely wound coil; its field is like a bar magnet's, and soft iron inside it becomes an electromagnet.

    A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. Its magnetic field lines are like those of a bar magnet: inside the solenoid they are parallel straight lines, showing a uniform field directed from the S end to the N end, and outside they leave the N end and curve round to enter the S end (see the figure). To magnetise a piece of soft iron, place it inside the solenoid and pass a current through the coil; the strong magnetic field inside magnetises it, and it becomes an electromagnet.

    Step-by-step solution →
16. Q156 CBSE 2024
    Explain in brief ​the ​function of an electric fuse ​in a domestic circuit. An electric heater of current rating 3 kW; 220 V is to be operated in ​an electric circuit of rating 5 ​A. ​What is ​likely to happen when the heater is switched ‘ON’ ? Justify your ​answer with necessary calculation.
    Show answer

    The heater draws about $13.6$ A, more than the 5 A rating, so the fuse melts and breaks the circuit.

    Function of a fuse: an electric fuse is a safety device connected in series in the live wire of a circuit; it is a wire of a metal or an alloy of suitable low melting point. When the current exceeds its rated value, because of overloading or a short circuit, the fuse wire heats up, melts and breaks the circuit, protecting the appliances and the wiring from damage. Calculation: the heater draws $I=\frac{P}{V}=\frac{3000\text{W}}{220\text{V}}\approx 13.6$ A. This is much more than the 5 A rating of the circuit, so switching the heater on overloads the circuit: the fuse wire melts and the circuit breaks, and the heater stops working. It should be used on the 15 A circuit.

    Step-by-step solution →
17. Q157 CBSE 2024
    A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he ​taps the drawing board gently and observes that the iron filings arrange themselves in a ​particular pattern.

    1. (a)Why do iron filings arrange in a particular pattern ?
    2. (b)What does the crowding of iron filings at the ends of the magnet indicate ?
    3. (c)​What do the lines, along which the iron filings align, represent ?
    4. (d)If the student places a cardboard horizontally in ​a current carrying ​solenoid and repeats the above activity, in ​what pattern would the iron filings arrange ? State the conclusion drawn ​about the ​magnetic field based on the observed pattern of the lines.
    Show answer

    Filings align along field lines; crowding at the poles shows the strongest field; inside a solenoid parallel lines show a uniform field.

    (a) The bar magnet exerts a force on the iron filings in the region around it — its magnetic field. Each filing becomes a tiny magnet and turns to lie along the direction of the field at its position; tapping lets the filings move freely, so together they arrange themselves in a definite pattern. (b) The crowding of the filings at the ends shows that the magnetic field is strongest near the poles of the magnet. (c) The lines along which the filings align represent magnetic field lines. (d) Inside the solenoid the iron filings arrange themselves in parallel straight lines (outside, the pattern is like that of a bar magnet). Conclusion: the magnetic field inside a current-carrying solenoid is the same at all points — it is uniform.

    Step-by-step solution →
18. Q158 CBSE 2024
    1. (a)​How is ​a ​solenoid prepared ? Differentiate between a ​circular coil and a solenoid.
    2. (b)​Draw the pattern ​of the magnetic field ​lines inside ​a current carrying solenoid. What does this pattern indicate ?
    Show answer

    A solenoid is insulated wire wound closely into a cylinder; its field inside is uniform, with straight parallel lines.

    (a) A solenoid is prepared by winding a long insulated copper wire closely, in many circular turns placed side by side, round a cylindrical tube, so that the coil takes the shape of a cylinder; its ends are connected to a battery through a key. Difference: a circular coil is a wire bent into a circle, with one or a few turns lying in one place, and its field lines are nearly circles near the wire and nearly straight only near its centre. A solenoid has many turns spread along the length of a cylinder; the field lines inside it are straight and parallel along its whole length, and outside its pattern is like that of a bar magnet, with one end acting as a north pole and the other as a south pole. (b) Inside a current-carrying solenoid the field lines are parallel, equally spaced straight lines along the axis, running from the S end to the N end; outside they leave the N end and return to the S end. This pattern indicates that the magnetic field is the same at all points inside the solenoid, that is, the field inside a solenoid is uniform.

    Step-by-step solution →
19. Q159 CBSE 2024
    1. (a)What happens when ​a bundle of wires of soft iron is placed inside the coil of a solenoid carrying a steady current ? Name the device obtained. ​Why is it called so ​?
    2. (b)Draw ​the ​magnetic field lines ​inside a current carrying solenoid. ​What does this pattern of magnetic field lines indicate ?
    Show answer

    The soft iron becomes a strong magnet, forming an electromagnet; the field inside a solenoid is uniform.

    (a) The strong magnetic field inside the current-carrying solenoid magnetises the soft iron, so the bundle becomes a strong magnet, one end north and the other south, as long as the current flows. The device obtained is an electromagnet. It is called so because it is a magnet produced by an electric current: it behaves as a magnet only while the current flows through the coil and loses its magnetism when the current is switched off. (b) Inside the solenoid the magnetic field lines are parallel straight lines running from the south-pole end to the north-pole end (outside, they curve from N to S). This pattern indicates that the magnetic field is the same at all points inside the solenoid, that is, the field inside is uniform.

    Step-by-step solution →
20. Q160 CBSE 2024
    “Earth wire is ​a ​safety measure ​in domestic electric ​circuits.” ​Justify this statement ​explaining its role in case of accidental leakage of electric appliances.
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    The earth wire gives leakage current a low-resistance path to the earth, so the user is not shocked and the fuse blows.

    The earth wire (green insulation) connects the metal body of an appliance to a metal plate buried deep in the earth, giving a low-resistance conducting path to the earth. If the insulation fails and the live wire touches the metal body (accidental leakage), the leakage current flows through the earth wire into the earth instead of through a person who touches the appliance. This keeps the potential of the body equal to that of the earth, so the user does not get a severe electric shock; the large current that flows also blows the fuse and cuts off the supply. Hence the earth wire is a safety measure, especially for appliances with a metal body such as an electric iron, toaster, table fan or refrigerator.

    Step-by-step solution →