If a coil is rotated in a magnetic field at twice the speed -- ie twice the frequency -- the amplitude of the emf induced in the loop

a. remain unchaged

b. reduce by half

c. double

C. double

Explanation:

The voltage of a EMF depends largely on the amount of spins that the coild is able to do, in this case as yuo are doubling the speed at which the coil is rotating you are also doubling the number of spins that the coil is doing in a certain amount of time, so the amplitude of the EMF induce on the loop will also double.

to treat tumors in the body

b would be the answer