A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be

Options

A. halved
B. the same
C. doubled
D. quadrupled

Answer

D

Explanation

power dissipated, `P = (e^(2))/(R )`
where e = induced e.m.f. ` = - ((d phi)/(dt))`
and `phi = NBA :. E = - ((dB)/(dt))`
Also `R prop (l)/(a) prop (l)/(r^(2))`
`:. P = (e^(2))/(R ) prop (N^(2) A^(2) r^(2))/(l) prop (N^(2) r^(2))/(l)`
As r is halved, and N is quadriupled
`:.` P is quadrupled.