A resistance `R` draws power `P` when connected to an `AC` source. If an inductance is now placed in series with the resistance, such that the impedence of the circuit becomes `Z`, the power drawn will be

Options

A. `P (R/Z)`
B. P
C. `P(R/Z)^2`
D. `Psqrt(R/Z)`

Answer

C

Explanation

Case I : `P = V_(rms)I_(rms)`
` = V_(rms) xx (V_(rms))/( R)`
`P = (V_(rms)^2)/( R) rArr V_(rms)^2 = PR` …..(i)
Case II : Power drawn in LR circuit

`P. = V_(rms)I_(rms) cos phi = V_(rms) xx (V_(rms))/(Z) xx R/Z`
` = V_(rms)^2 ( R)/(Z^2) = PR xx (R )/(Z^2)`
`P. = P (R^2)/(Z^2)`