Question

Ratio of magnetic field at the centre of a current carrying coil of radius R and at a distance of 3R on its axis is

• A. $10 \sqrt { 10 }$
• B. $20 \sqrt { 10 }$
• C. $2 \sqrt { 10 }$
• D. $\sqrt { 10 }$

Answer 1

Answer: (A)

$10 \sqrt { 10 }$

Answer 2

By using $\frac { B _ { \text {centre } } } { B _ { \text {axis } } } = \left( 1 + \frac { x ^ { 2 } } { r ^ { 2 } } \right) ^ { 3 / 2 }$where x = 3R and r = R

⇒ $\frac { B _ { \text {centre } } } { B _ { \text {axis } } } = ( 10 ) ^ { 3 / 2 } = 10 \sqrt { 10 }$ .