Question

A long wire passes through amperian loop of radius $R$ along its plane as shown. Then $\oint\overset{ \rightarrow }{B}\cdot \overset{ \rightarrow }{d l}$ for amperian loop is

• A. $\mu _{0}I$
• B. $\frac{\mu _{0} I}{2 \pi R}$
• C. $\frac{\mu _{0} I}{4 \pi R}$
• D. zero

Answer 1

Answer: (D)

From Ampere's law, $\oint\overset{ \rightarrow }{B}\cdot \overset{ \rightarrow }{d l}=\mu _{0}i_{inside}$
As $i_{inside}=0$ . Hence, $\oint\overset{ \rightarrow }{B}\cdot \overset{ \rightarrow }{d l}=0$