Question

Name and define the S.I. unit of time. How is it related to (i)minute (ii)hour (iii)day and (iv)year?

Answer 1

We need to understand the standard international unit used to measure the time quantity. Knowing this we can relate the other quantities which are used for the same purpose on different scales to measure the time as required in this problem.

Complete answer:
We know that time is the basic physical quantity that helps us understand the duration of another quantity or the comparative scale of how long or when. The seconds is regarded as the S.I. unit of the physical quantity time. The unit ‘second’ is defined as the time taken for Caesium-133 atoms to undergo 9,192,631,770 ground state transitions. We have both larger and smaller scales of measuring time. Some of them are given below.
(i)Minute: It is defined as a time interval which is equal to sixty seconds. It is also one-sixtieth of an hour. We can give the relation between the minute and seconds as –
$\text{1 minute}=60\ \text{seconds}$
(ii)Hour: It is defined as the time interval which is equal to 60 minutes. It is also the one-twenty fourth of a day. The relation between an hour and seconds is given as –

& \text{1 hour}=60\text{ minutes} \\\ & \therefore \text{1 hour =3600 seconds} \\\ \end{aligned}$$ (iii)Day: It is the time taken for the earth to rotate once on its axis. It is defined as twenty-four hours. We can relate one day to the seconds as – $$\begin{aligned} & \text{1 day}=24\text{hours} \\\ & \Rightarrow \text{1 day = 24}\times \text{3600 seconds} \\\ & \therefore \text{1 day = 86400 seconds} \\\ \end{aligned}$$ (iv)Year: It is defined as the time taken for earth to undergo one complete revolution around the sun. It normally consists of 365days normally. We can relate the year and the seconds as – $$\begin{aligned} & \text{1 year = 365 days} \\\ & \Rightarrow \text{1 year = 365 }\times \text{ 86400 seconds} \\\ & \therefore \text{1 year = 31,536,000 seconds} \\\ \end{aligned}$$ So, we get the relation of the seconds with all the larger time scales. This is the required solution. **Note:** The revolution around the sun for earth takes three hundred sixty-five days and a one-fourth of a day. We usually neglect this one-fourth and add up the quarter once in four years to give a complete day and this year becomes the leap year.