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?
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
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:
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
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