Question

Two solenoids having lengths L and 2L and the number of loops N and 4N, both have the same current, then the ratio of the magnetic field will be

• A. $1 : 2$
• B.
• C.
• D.

Answer 1

Answer: (A)

$1 : 2$

Answer 2

$B = \mu _ { 0 } \frac { N } { L } i$ $\Rightarrow B \propto \frac { N } { L }$

$\Rightarrow \frac { B _ { 1 } } { B _ { 2 } } = \frac { N _ { 1 } } { N _ { 2 } } \times \frac { L _ { 2 } } { L _ { 1 } } = \frac { N } { 4 N } \times \frac { 2 l } { L } = \frac { 1 } { 2 }$.