Question

A solenoid of n turns carries current I while another solenoid of same length and of $3$ n turns carries current $4I.$ What is the ratio of the magnetic strengths of the two solenoid ?

• A. $12times$
• B. $10times$
• C. $7times$
• D. none of the above

Answer 1

The correct option is A $12times$

The magnetic field inside a current carrying solenoid is given by

$B={\mu }_{0}nI$

where $n$ is the number of turns per unit lenght in the solenoid

$I$ is the current through the wire

Hence $\frac{B^{\prime }}{B}=\frac{n^{\prime }{I}^{\prime }}{nI}=3\times 4=12$