Question

Unit of power is
(A). watt per second
(B). joule
(C). watt
(D). none of these

Answer 1

- Hint: Power is a measure of how much energy is utilized to complete the given work. So, you can convert the formula of work and time and get the unit of power in the MKS (Meter Kilogram Second) system.

Complete step-by-step solution -

In our daily routine, we sell and buy so many things. In this case, we make sure what we take or give is in a specific amount. For instance, when we want to buy some fruits, we denote them in kg, in the same way, when you purchase some water bottles, you denote them in litres. So, basically the quantity is important for anything you deal with in your daily routine that makes you easy in calculations.
In this regard, there are certain standards being created and are called Units. These units are categorized and recognized as S.I units (International System of Units)
Before, we derive the formula for power, let us understand what is power. To do work, we need energy and the energy we spend in this regard when measured with respect to time, gives us power.
To derive a power unit, we need to consider the formula of power, so, from the definition of power, we can write power in terms of energy and time. If P is power, E is energy spent to do work, and T is time taken to do work, then power is given as,
$P=\dfrac{E}{T}$,
Since, energy is measured in joules and time is measured in seconds, we can say that the unit of power is joule per second which is nothing but one watt. Hence, we even understood the definition of one watt, which means one joule of energy at a rate of one second of time.
Hence,
\[P=\dfrac{E}{T}=\dfrac{\text{1joule}}{\text{1second}}\text{=1watt}\]

Note:- Power can be expressed as Energy and Time and its unit is Watt.
In general, power is expressed in terms of voltage (V), current (I) and resistance (R) and the formula is P=VI, $P={ I }^{ 2 }R$.