Q: The number of turns in a long solenoid is 500. The area of cross-section of solenoid is 2 × 10–3 m2 . If the value of magnetic induction, on passing a current of 2 amp, through it is 5 × 10–3 tesla, the magnitude of magnetic flux connected with it in weber will be
(A) 5 × 10–3
(B) 10–2
(C) 10–5
(D) 2.5
Solution : Magnetic flux , $\displaystyle \phi = N B A$
$\displaystyle \phi = 500 \times 5 \times 10^{-3} \times 2 \times 10^{-3}$
$\displaystyle \phi = 5 \times 10^{-3} Wb $