Magnetic Field of a Solenoid
Mohan tightly wound a very long copper wire on a PVC pipe and carefully took the pipe out. The two ends of the copper wire then attached to a battery.
This cylindrical shape of copper wire showed few properties of a bar magnet. Later he found that it is called a solenoid and this solenoid is used in several devices such as door bell, relay switch etc. The magnetic field of a solenoid is given below.

The magnetic field strength of a solenoid having n turns is `B=mu_0nl`, where, `I` is the current flowing in the solenoid.
A long solenoid having 400 turns is used as electromagnet. If `1.5 A` current is flowing through the solenoid, the strength of the electromagnet is
Options:
(a) `0.2 mT`
(b) `0.4m T`
(c) `0.6 mT`
(d) `0.8 mT`