NCERT Class 10 Science — Chapter 4: Magnetic Effects of Electric Current

mcqmedium

Which among the following is the most direct observable consequence of a current-carrying conductor placed in a transverse magnetic field?

Official previous-year question

Verified 1 Aug 2026.

Options

AA rise in the conductor’s temperature only
BA change in the conductor’s resistance
CA reversal of current direction
DA sideways displacement of the conductor

Did you get this right?

Solution

The correct option is A sideways displacement of the conductor.

Explanation

When a current-carrying conductor is placed in a magnetic field, the moving charge carriers within the conductor experience a magnetic force known as the Lorentz force. The cumulative effect of this force on the charge carriers is transmitted to the conductor itself, resulting in a mechanical force acting on the wire.

Detailed Analysis:

A sideways displacement of the conductor is Correct: According to the principles of electromagnetism (specifically the motor effect), a conductor carrying current ($I$) placed in a transverse magnetic field ($B$) experiences a force ($F$) given by the equation $F = I(L \times B)$. Since the field is transverse (perpendicular), the magnitude of the force is maximum ($F = BIL$). This force acts perpendicular to both the current and the magnetic field, causing a sideways physical displacement of the conductor.
A rise in the conductor’s temperature only is Incorrect: A rise in temperature is primarily caused by the heating effect of electric current (Joule heating, $H = I^2Rt$) due to the conductor's resistance. While this occurs, it is a consequence of current flow itself, not specifically the presence of the external magnetic field.
A change in the conductor’s resistance is Incorrect: The resistance of a conductor is determined by its material properties, dimensions, and temperature. Placing it in a magnetic field does not directly alter its ohmic resistance in a standard macroscopic context (ignoring the Hall effect or magnetoresistance, which are secondary or specific phenomena).
A reversal of current direction is Incorrect: The magnetic field exerts a mechanical force on the conductor but does not alter the polarity of the voltage source driving the current. Therefore, it does not reverse the current direction.

Key Takeaway:
A current-carrying conductor placed in a magnetic field experiences a mechanical force perpendicular to the plane of the current and the field, a phenomenon governed by Fleming’s Left-Hand Rule.

Your note

More from Chapter 4: Magnetic Effects of Electric Current

With reference to magnetic field lines, consider the following statements: 1. Outside a magnet, they are taken to originate from the north pole and terminate at the south pole. 2. Inside a magnet, they run from the south pole to the north pole. 3. The closeness of lines is independent of the relative strength of the field. 4. Two magnetic field lines can intersect at a point. Which of the statements given above is/are correct?

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Assertion (A): Magnetic field is a vector quantity. Reason (R): Magnetic field lines are closer together where the magnetic field is strong.

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Assertion (A): The magnetic field is stronger near the poles of a magnet. Reason (R): The magnetic field lines are widely spaced near the poles.

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Which of the following changes will increase the displacement of a current-carrying rod in a uniform magnetic field? 1. Increasing the current reduces the displacement of the rod. 2. Using a stronger magnet. 3. Increasing the effective length within the field has no effect on displacement. Which of the statements given above is/are correct?

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Which medical imaging technique relies on strong magnetic fields and radio waves?

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The correct option is A sideways displacement of the conductor.

Explanation

Detailed Analysis:

A sideways displacement of the conductor is Correct: According to the principles of electromagnetism (specifically the motor effect), a conductor carrying current ($I$) placed in a transverse magnetic field ($B$) experiences a force ($F$) given by the equation $F = I(L \times B)$. Since the field is transverse (perpendicular), the magnitude of the force is maximum ($F = BIL$). This force acts perpendicular to both the current and the magnetic field, causing a sideways physical displacement of the conductor.
A rise in the conductor’s temperature only is Incorrect: A rise in temperature is primarily caused by the heating effect of electric current (Joule heating, $H = I^2Rt$) due to the conductor's resistance. While this occurs, it is a consequence of current flow itself, not specifically the presence of the external magnetic field.
A change in the conductor’s resistance is Incorrect: The resistance of a conductor is determined by its material properties, dimensions, and temperature. Placing it in a magnetic field does not directly alter its ohmic resistance in a standard macroscopic context (ignoring the Hall effect or magnetoresistance, which are secondary or specific phenomena).
A reversal of current direction is Incorrect: The magnetic field exerts a mechanical force on the conductor but does not alter the polarity of the voltage source driving the current. Therefore, it does not reverse the current direction.