Question

A 10N force acts on a rectangular conductor of 5 cm long placed perpendicular to a magnetic field . if the current in conductor is 50A ,then B

Answer 1

Given :

Force =10N

Length of the conductor= 5cm=5/100 m

Current =I=50 A

B=?

Use the formula 
F=BIL

B=F/IL

=10x100/50x 5

=4 Tesla 

Therefore B= 4 tesla

Answer 2

We have the formula for force acting on a conductor as F = B I L sinθ

Here, it is given that F = 10 N
Length of the conductor (L) =  5 cm = 5 * $10^{-2}$ m
I = 50 A
Since the conductor is placed perpendicular to the magnetic field, θ = 90°

Therefore, B = F / I L sinθ
B = 10 / 50 * 5 * $10^{-2}$  * sin 90°
B = 10 / 250 *  $10^{-2}$ * 1
On shifting  $10^{-2}$  to the numerator, it becomes  $10^{2}$ 
B = 10 *  $10^{2}$  / 250
B = 1000/250
B = 4 Tesla

Therefore, B = 4 T is the required answer.