Question

Assertion Magnetic field due to an infinite straight conductor varies inversely as the distance from it.
Reason The magnetic field at the centre of the circular coil in the following figure is zero.

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

Answer 1

Answer: (B)

The magnetic field at a point due to current flowing through an infinitely long conductor is given by
$B=\frac{\mu_{0}}{4 \pi} \cdot \frac{2 I}{a}$
where $a$ is the distance of that point from conductor. Now according to right hand thumb rule it follows that magnetic field is in the form of concentric circles, whose centres lie on the straight conductor.