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Electrical power of a lightbulb

  • #1

Homework Statement


Two identical light bulbs are connected to the ends of the battery. In the first case they are connected in series and in the second they are connected in parallel mode. What is the ratio of the electrical power of light bulbs connected as mentioned?

Homework Equations


##P=I^2R##
##P=\frac{V^2}{R}##

The Attempt at a Solution


Since the voltage is the same and i take a light bulb to be a resistor shouldnt it just be ##R_1/R_2##? It somehow should be 1/4 but i dont get how. Total resistance in the first case is ##2R## and in the second is ##2/R## right?
 

Answers and Replies

  • #2
cnh1995
Homework Helper
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In the second case, total resistance is not 2/R. What is the formula for equivalent resistance of two parallel resistors?
 
  • #3
In the second case, total resistance is not 2/R. What is the formula for equivalent resistance of two parallel resistors?
Parallel resistors ##1/R_t = 1/R+1/R## so its ##R/2## so its ##1/4## oh thanks!
 

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