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# Which of the following is not the unit of time?A.) HourB.) Nano secondC.) $\mu$ secondD.) Light year

Last updated date: 26th Feb 2024
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Hint: The unit of a physical quantity is an arbitrarily chosen standard which is widely accepted by the society and in terms of which other quantities of similar nature may be measured.
A unit of time is any particular time interval, used as a standard way of measuring or expressing duration.
In this question, we will check which of the given options is not representing the unit of time.

Complete Step by step complete answer
SI unit of time is second. Other important units of time are minute, hour, day, week, month and year.
So, 1 Nano second = ${{10}^{-9}}$ second
1 microsecond = ${{10}^{-6}}$
Thus, options A, B, C are units of time.
On the other hand, light year is the unit used to describe astronomical distances. It is defined as the distance travelled by light in one earth year.
Thus, option D is the correct answer.

Also note that the light year is used to measure the distance of astronomical objects and one light year is equivalent to about $9\cdot 46$ trillion kilometres (or $5\cdot 88$ trillion miles).