Question

Assertion : The net magnetic force on a current loop in a uniform magnetic field is zero but torque may or may not be zero
Reason : Torque on a current carrying coil in a magnetic field is given by $\vec{\tau }=nI\left(\vec{A}\times \vec{B}\right)$.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

Since the net torque acting on a current carrying coil is given by:
$\tau =nI(\vec{A}\times \vec{B})$
where, $\vec{A}$ is the area of cross-section through which the magnetic field $\vec{B}$ passes.
The net force acting on the coil might be zero but it can produce a torque on the coil if it acts in the opposite direction.
Here, assertion and reason both are correct but reason is not the correct explanation of assertion.