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Magnetic Effects of Electric Current

CBSE Class 10 · Science · Chapter 12

Past board exam questions

CBSE 2027 sample paper · 3 marks

A. State the Right-Hand Thumb Rule and describe how it helps determine the direction of magnetic field around a current-carrying conductor. B. Explain how the magnetic field changes with distance from the conductor.

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A. 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. So, if the thumb of the right hand points in the direction of the conventional current, the curled fingers show the direction of the magnetic field lines (concentric circles) around the conductor; this is how the direction of the field is found. B. The magnitude of the magnetic field produced by a long straight conductor decreases as the distance from it increases: B∝(I)/(r), i.e. it is inversely …

CBSE 2027 sample paper · 4 marks

A school has installed an automatic electromagnetic door-locking system at the main entrance. The locking mechanism uses a solenoid controlled by a switch at the security desk. When electricity flows through the solenoid, it creates a magnetic field strong enough to pull an iron bolt, unlocking the door. As soon as the switch is turned off, the magnetic field disappears, and a spring pushes the bolt back, locking the door. A. Why is an iron core kept inside the solenoid in this locking mechanism? B. How can we determine the magnetic poles in this solenoid? C. If the current in the solenoid is increased from 1 A to 2 A, explain how the magnetic effect changes and its effect on unlocking the door.

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A. A soft iron core placed inside the solenoid gets magnetised and concentrates and strengthens the magnetic field (making a strong electromagnet), producing a stronger pull on the bolt; being soft iron, it loses its magnetism as soon as the current is switched off. B. Using the right-hand thumb rule: curl the fingers of the right hand in the direction of the current in the coil; the thumb then points towards the north pole of the solenoid. (Alternatively, bring the known north pole of a bar magnet near one end of the solenoid: repulsion shows that end is a north pole.) C. The magnetic field inside a solenoid is directly proportional to the current, so doubling the current from 1 A to 2 A …

CBSE 2027 sample paper · 4 marks

A school has installed an automatic electromagnetic door-locking system at the main entrance. The locking mechanism uses a solenoid controlled by a switch at the security desk. When electricity flows through the solenoid, it creates a magnetic field strong enough to pull an iron bolt, unlocking the door. As soon as the switch is turned off, the magnetic field disappears, and a spring pushes the bolt back, locking the door. A. Why is an iron core kept inside the solenoid in this locking mechanism? B. How can we determine the magnetic poles in this solenoid? D. If the source of the current is fixed, how can we increase the magnetic field in the solenoid?

Show answer
A. A soft iron core placed inside the solenoid gets magnetised and concentrates and strengthens the magnetic field (making a strong electromagnet), producing a stronger pull on the bolt; being soft iron, it loses its magnetism as soon as the current is switched off. B. Using the right-hand thumb rule: curl the fingers of the right hand in the direction of the current in the coil; the thumb then points towards the north pole of the solenoid. (Alternatively, bring the known north pole of a bar magnet near one end of the solenoid: repulsion shows that end is a north pole.) D. (Any two) Increase the number of turns of the coil; reduce the length of the coil (wind the turns more closely); insert …

CBSE 2026 board paper · 1 mark

During a lab experiment, Bhavna uses a solenoid connected to a battery. She notes down the following facts : (i) The pattern of magnetic field lines inside the solenoid is similar to a bar magnet. (ii) The north pole and south pole of the current-carrying solenoid can be identified by applying the right hand thumb rule. (iii) A solenoid can be used to magnetise a piece of a soft iron, making it an electromagnet. Choose the option enlisting all the correct statements :

  1. (i) and (iii)
  2. (ii) and (iii)
  3. (i) and (ii)
  4. (i), (ii) and (iii)
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(i), (ii) and (iii)

CBSE 2026 board paper · 1 mark

Assertion (A) : Direction of force exerted on a current-carrying conductor placed in a magnetic field remains same if the directions of both magnetic field and current flowing through the conductor are reversed. Reason (R) : The direction of force exerted on a current-carrying conductor placed in an external magnetic field can be determined by using magnetic compass.

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

CBSE 2026 board paper · 1 mark

Assertion (A) : The needle of a compass, kept in an external magnetic field, always aligns itself in the North-South direction of the Earth. Reason (R) : The behaviour of the needle of the compass is similar to the behaviour of a freely suspended bar magnet.

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

CBSE 2026 board paper · 1 mark

Assertion (A) : With the help of compass, magnetic field lines can be traced outside the bar magnet. Reason (R) : The north pole of a compass needle always points towards the south pole of the magnet when brought close to it.

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

CBSE 2026 board paper · 1 mark

Assertion (A) : The needle of a magnetic compass kept in strong external magnetic field, always aligns itself in north-south direction on the earth. Reason (R) : Behaviour of the needle of a compass is same as that of a freely suspended bar magnet.

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