The moving coil of a galvanometer made of 200 turns of thin wire is suspended from an elastic thread. The area of the coil is `1 cm^2,` it coincides in direction with the lines of induction of a magnetic field with induction of 15 mT. When the current of 5.0 A is passed through the coil it turns through `15^@.` By what angle will the coil turn with a current of `7.5 muA?` What is the torsion modulus of the thread?

Answer

`22.5^@, 10^(-10), N.m//deg=5.7 xx 10^(-9)N.m//rad`.

Explanation

A torque `M=wiSB` acts on the moving coil balanced by a torque M `f_(alpha)` due to the elasticity of the twisted thread, where is the torsion inodulus. Equating, we obtain `j alpha=W//SB` from which we see that, other conditions being equal, the coils angle of rotation is proportional to the current.