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The electric power consumed by a device may be calculated by using either of the two expressions P = I2R or P = V 2/R . The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained.

The electric power consumed by a device may be calculated by using either of
the two expressions P = I2R or P = V 2/R . The first expression indicates that it is
directly proportional to R whereas the second expression indicates inverse
proportionality. How can the seemingly different dependence of P on R in these
expressions be explained.

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1 Answers

aditya suman
39 Points
13 years ago

The expression P=I2R IS USED ONLY WHEN RESISTANCES ARE CONNECTED IN SERIES BECAUSE IN SERIES COMBINATION CURRENT IN EACH RESISTANCE IS CONSTANT

FOR EXAMPLE : IF R & R' ARE CONNECTED IN SERIES & I CURRENT IS PASSING THROUGH BOTH OF THEM THEN TOTAL POWER P=I2R+I2R'

P=P+P' THIS IS THE EXPRESSION FOR POWER WHEN RESISTANCES ARE CONNECTED IN SERIES

SIMILARLY WHEN RESISTANCES ARE CONNECTED IN PARALLEL THEN POWER BECOMES INVERSELY PROPORTIONAL TO R BECAUSE VOLTAGE IS CONSTANT IN THIS CASE

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