Question

At a distance of 10 cm from a long straight wire carrying current, the magnetic field is 0.04 T. At the distance of 40 cm, the magnetic field will be

• A. 0.01 T
• B. 0.02 T
• C. 0.08 T
• D. 0.16 T

Answer 1

Answer: (A)

0.01 T

Answer 2

$B \propto \frac { 1 } { r } \Rightarrow \frac { B _ { 1 } } { B _ { 2 } } = \frac { r _ { 2 } } { r _ { 1 } } \Rightarrow \frac { 0.04 } { B _ { 2 } } = \frac { 40 } { 10 } \Rightarrow B _ { 2 } = 0.01 \mathrm {~T}$