Question

$P = \dfrac{{{V^2}}}{R}$ is applied when
(1) Current is constant
(2) Potential difference is constant
(3) Resistance is constant
(4) None

Answer 1

Hint When in the circuit only resistors are present, then real power comes into action. With capacitors and inductors, reactive power comes into action. That is why in both cases the answers do not match.

Complete step by step solution
Power : Electrical Power in a circuit is the rate at which energy is produced or absorbed within a circuit. Any source of energy such as a voltage will produce or deliver power while the connected load absorbs it.
In simple words, If a current I flows through through a given element in your circuit, dropping voltage V in the process, then the power dissipated by that circuit element is the product of that current and voltage. Power is represented by P.
And the formula is given by :
$P = V \times I$
And we can use ohm’s law that is ( $V = I \times R$ ) and form the other relationship of this formula
$P = {I^2}R$
Or
$P = \dfrac{{{V^2}}}{R}$
When applied potential difference is constant, we use $P = \dfrac{{{V^2}}}{R}$
When current flowing is constant then we use $P = {I^2}R$
As resistance is always constant
We use $P = V \times I$ only when both the current as well as voltage is constant across the element or circuit.

The correct option is: Potential difference is constant.

Note All the formulas are correct or are just re-arrangements of each other using Ohm’s law. Before using the formula always observe which value is constant (voltage or current) as resistance is constant. So in the formula you use, your values used must be constant for the interval you want to calculate the power.