Question

(a) Define 1 watt of power.
(b) A lamp consumes 1000J of electrical energy in 10s. What is its power?
(c) Define average power.

Answer 1

Hint: So, we have a question with three sub parts here. Two of them are basic definitions of physical quantities which one could easily recall and write down. Now for the second sub question, note down the given values and substitute in the expression for power so as to get the answer.

Formula used:
Power,
$P=\dfrac{W}{t}$

Complete step-by-step solution:
(a) Here, we are asked to define 1watt of power. For that let us define what power is. Power is actually defined as the rate at which work is done or in other words, work done per unit time is power and Watt is the SI unit of this quantity.
When the work done for the duration of 1s is found to be 1J, then the power is said to be 1watt.
(b) In the question, we are given the energy consumed by a lamp to be 1000J within the duration of 10s. We are asked to find the power of the lamp using this information.
We have the expression,
$P=\dfrac{W}{t}$
Substituting the given values,
$P=\dfrac{1000J}{10s}$
$\therefore P=100watt$
Therefore, we found the power to be 100watt.
(c) Average power could be defined as the ratio of total work done by a certain body to the total time taken by the body to do that work.

Note: 1 watt could be considered equivalent to 1joule-second from the very definition of power. The SI unit of average power is known to be kilowatt hour. Another definition for power is the energy that is being transferred for a time interval t. This is basically the same definition as that mentioned in the question.