Question -
An electric bell has a rating of 500 W 100 V. It is used in a circuit having a 200 V supply. What resistance must be connected in series with the bulb so that it delivers 500 W?
Options:
A .  10 ohm
B .  20 ohm
C .  30 ohm
D .  40 ohm
Answer: Option B : B The current flowing in the bulb of 500Woperating at 100V is I=500100=5A resistance of bulb =1005=20 ohm say R1 to deliver 500W the current in the bulb must remain 5 A when it is operated with 200V supply the resistance R to be connected in series for this purpose is given by 200R1+R2=5 R1+R2=40 R1+20=40 R=20ohm
Submit Your Solution hear: