Physics-
General
Easy
Question
Four identical electrical lamps are labelled 1.5V, 0.5A which describes the condition necessary for them to operate at normal brightness. A 12V battery of negligible internal resistance is connected to lamps as shown, then
- The value of R for normal brightness of each lamp is (3/4) W
- The value of R for normal brightness of each lamp is (21/4) W
- Total power dissipated in circuit when all lamps are normally bright is 24W
- Power dissipated in R is 21W when all lamps are normally bright
The correct answer is: The value of R for normal brightness of each lamp is (21/4) W
For normal brightness of each bulb see following circuit. Current through each bulb = 0.5 A
So main current 
Also, voltage across the combination 
So voltage across the resistance 
Hence for resistance 
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