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Identify the incorrect statements from the following. (A) A charged particle of charge e is moving through a magnetic field, work will be done by the magnetic field on the charge. Choose the correct answer from the options given below: |
(A) and (B) only (A) and (C) only (C) and (D) only (A) and (D) only |
(A) and (D) only |
The correct answer is Option (4) → (A) and (D) only Analysis of each statement: (A) A charged particle of charge $e$ is moving through a magnetic field, work will be done by the magnetic field on the charge. Magnetic force on a moving charge: $\vec{F} = q (\vec{v} \times \vec{B})$ The force is always perpendicular to the velocity of the charge, so no work is done by the magnetic field. ❌ Statement (A) is incorrect. (B) A conductor with free electrons is placed in a magnetic field. No current is flowing through the conductor. No magnetic force acts on the conductor. If no current flows, there is no net motion of charges, so the conductor experiences no magnetic force. ✅ Statement (B) is correct. (C) A charged particle is moving perpendicular to the magnetic field. The magnetic force does not change the speed of the particle but changes its direction. Force is perpendicular to velocity → circular motion. Speed remains constant, direction changes. ✅ Statement (C) is correct. (D) A charged particle is moving in a straight line without any change of direction. It shows that no magnetic field is there. If the particle’s velocity is parallel or antiparallel to the magnetic field, the magnetic force is zero, and it moves in a straight line even in the presence of a magnetic field. Hence, the statement is incorrect. Answer: (A) and (D) are incorrect |
