Question

$P=\dfrac{{{V}^{2}}}{R}$ is applied when
A) Current is constant
B) Potential difference is constant
C) Resistance is constant
D) None

Answer 1

Electromagnetic force is the force that causes an electric current to flow in an electric circuit while the potential difference (Pd) between two points in an electric current is that difference in their electrical state which tends to cause flow of electric current between them. Volt is a unit of electromotive force.

Complete step-by-step solution:
Electric power is defined as the rate per unit time, at which electrical energy is transferred by a circuit. Electric power is produced by an electric generator and SI unit of power is watt. Electric power is a scalar quantity which does not have any direction.
Electric current is defined as the time rate of net motion of an electric charge across a cross-sectional boundary. A random motion of electrons in a metal does not consume current unless there is a net transfer of charge with time
Electric current (I) =Rate of transfer of electric charge
$I=\dfrac{dQ}{dt}$
Power is defined as the product of voltage and current
Power is expressed in terms of watts and is given as
$P=V\times I={{I}^{2}}Rwatts$
At constant potential difference power is given as:
$P=\dfrac{{{V}^{2}}}{R}$
So the correct option is B.

Note: Students the watt is often found to be inconveniently small and so a bigger unit, the kilowatt is frequently used as the unit of power.1kilowatt (kW) =1000 watts or joules per second. Electrical energy is expressed in terms of kilowatt-hour (kWh) and 1kwh=1000watt-hours=3.6MJ. SI unit of current is ampere (A).