Question

The force on a wire carrying 8.75 A is a maximum of 1.28 N when placed 

between the pole faces of a magnet. If the pole faces are 75.4 cm in 

diameter, what is the approximate strength of the magnetic field? 

Answer 1

We know that Ampere's force is

$$F=IBL,\\\space\\ B=\frac{F}{IL}=\frac{1.28}{8.75·0.754}=0.194\text{ T}.$$