The electric power consumed by a device may be calculated by using either of the two expressions : `P = I^2 R` 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 ?

Explanation

Both the expressions `(P = I^2 and P = V^2//R)` are correct and are used to calculate electric power. The experssion `P = I^2 R` is used ton calculate electric power when the current flowing through the circuit is constant. This is the case when the electric devices are connected in series. The expression `P = V^2//R` is used to calculate electric power when the pd (v) across the circuit is constant. This is the case when the electric devices are connected in parallel.