I=P/V
I=500/10=5A
Resistance of bulb,R1=100/5=20 ohm
Resistance,r to be connected in series,
5A=200/R1+R2
R1+R2=200/5
R1+R2=40
20+R2=40
R2=20 ohm
Anonymous I=500/100 instead of 500/10
an electric bulb rated 50W at 100V is used in a circuit having a 200V supply. What resistance R must be put in series with the bulb so that then bulb delivers 500W?
TH ANSWER IS 10
I=P/V
I=500/10=5A
Resistance of bulb,R1=100/5=20 ohm
Resistance,r to be connected in series,
5A=200/R1+R2
R1+R2=200/5
R1+R2=40
20+R2=40
R2=20 ohm