The electric power consumed by a device may be calculated by the using either of the two expressions P = I2R or P = V2/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.
Both the expressions are correct. In the first case where P = I2R current (I) remains constant. Whereas in the second expression where P = V2/R the Voltage (V) remains constant.
Therefore P = I2R is used where the resistors are connected in series because in the series connection the current in each resistance is constant.
P = V2/R is used where the resistors are connected in parallel because in the parallel connection the voltage in each resistance is constant. So power becomes inversely proportional to resistance.