Question

When a work of 1 joule($1J$) is done in 1s, the power is:
 (A) One kilowatt
 (B) One watt
 (C) One watt-second
 (D) One joule

Answer 1

HINT In this question use the direct formula that energy is the product of power consumed by the equipment and the time for which the equipment is running that is $E = P \times t$. Use the respective units of energy and time and substitute the values given in the problem to get the required power.

Complete step by step solution
As we know that the capacity of doing work is called energy consumed by the system and it is often measured in joule.
And we all know that the energy consumed is equal to the product of power consumed by the equipment and the time interval (t) i.e., how long the equipment is running.
$ \Rightarrow E = P \times t$ ………………. (1)
Where, E = energy consumed.
P = power of the equipment and t= time interval
Now it is given that $1J$ of work is done in 1 sec.
Therefore, energy consumed = $1J$
And the time interval in which this energy is consumed = 1sec
Therefore, E = $1J$and \[t = 1sec.\]
Now substitute this value in equation (1) we have,
$ \Rightarrow 1 = P \times 1$
Now simplify this we have,
Therefore, $P = \left( {\dfrac{1}{1}} \right) = 1J/s$
Another form of joule per sec (J/s) is watts having symbol (W)
Therefore, $P = 1Watt(W)$
So, the power spent is equal to 1W
So, this is the correct answer.

Hence option (B) is the correct answer.

NOTE Power is defined as the rate of doing work whereas energy is simply the capacity of doing work. The S.I unit of power is watt and that of energy is joule. So, if we use the formula constraints then we get to know that $J/s = Watt$. Time in such problem are standardize taken in seconds and not in hours or minute so if time is given in units others than sec is advised to convert this to sec using basic unitary transformation that
$1\min = 60\sec and 1 hour = 60\min $