It takes `16 min` to boil some water in an electric kettle. Due to some defect it becomes necessary to remove `10 %` turns of the heating coil of the kettle . After repairs , how much time will it take to boil the same mass of water ?

Options

A. `17.7 min`
B. `14.4 min`
C. `20.9 min`
D. `13.7 min`

Answer

B

Explanation

If `N` is the initial number of turns in the coil and `r` is the radius of coil, then its resistance is
`R = rho(L)/(A) = rho (N 2 pi r )/(A) or (V^(2) t A ) /( 4.2 rhoN 2 pi r ) = Q = msd theta`or `(t)/(n) = ( msd theta xx 4.2 rho 2 r )/( V^(2) A) = constant`
or `(t_(1) // N_(1))/( t_(2)//N_(2)) = 1 or t_(2) = (N_(2))/(N_(1)) t_(1) = ((( 9)/( 10) N_(1))/(N_(1))) t_(1) = ( 9) /( 10) xx 16 min`