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Electrical power of a lightbulb

  1. Jun 19, 2016 #1
    1. The problem statement, all variables and given/known data
    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?
    2. Relevant equations
    ##P=I^2R##
    ##P=\frac{V^2}{R}##
    3. 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?
     
  2. jcsd
  3. Jun 19, 2016 #2

    cnh1995

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    Homework Helper

    In the second case, total resistance is not 2/R. What is the formula for equivalent resistance of two parallel resistors?
     
  4. Jun 19, 2016 #3
    Parallel resistors ##1/R_t = 1/R+1/R## so its ##R/2## so its ##1/4## oh thanks!
     
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