Question

Find the value of resistance connected in a series with a bulb 60watt, 30 volt to run on 90volt supply

Answer 1

Explanation:

resistance of is

P = V²/ R

R = V²/P = ( 30x 30)/60 = 15 ohm

if applied voltage is 90v

then pd across bulb is

V = IR

30 = I x 15

I = 30/15 = 2A

thus pd across a resistor which is connected with bulb in order to drop only 30 v across bulb.

V = I x r

60 = 2 x r

r = 30ohm

Answer 2

Answer:30 Ohm

Explanation:Resistance of bulb, R=V^2/P

R=30*30/60=15 Ohm

current,I will be same as they are in series

Therefore, I=V/R = 2A

For 90 volt supply E=IZ

90-30=60v

R=60/2=30 Ohm