## Note on Measurement of Time

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#### Measurement of time

The duration between any two events is called time. The SI unit of time is second. In a pendulum clock, the oscillation is made for the measurement of time. One second is defined as the 1/86,400 th part of the mean solar day. A particular point in the space is called zenith. A solar day is defined as the time interval between the consecutive passages of the sun through the zenith.
The time taken by the earth to revolve once around the sun is called one year. Large distances such as the distance between the earth and the moon etc. are measured in the light year. It is the distance travelled by light in one year.

We have,

1 year = 365 days = 365 × 24 h = 365 × 24 × 3600 s = 31,536,000 s
Since the speed of the light in air or vacuum is 3× 108m/s
And distance travelled = speed × time
Therefore, 1 light year = 3 ×108× 31,536,000 s
= 9.4608 × 1015m

One standard second is defined as the time taken by cesium -133 atom to make 9192631770 vibrations. The watch based on such vibrations is called an atomic watch. Scientists use an atomic clock for the measurement of time.In quartz, watch time is measured by the oscillation of the pendulum and in an electronic watch, time is measured by frequency of alternating current. Automatic watch or mechanical watch may gain or lose time by few seconds or minutes in a day

Activity

You must have a clock in your home. Set the time of your clock according to the time of the news program of the radio. Then observe the time of your clock and news program of the radio after 1 month. What do you observe? Discuss with your friends and with your teachers.

• The duration between any two events is called time.
• The SI unit of time is second.
• One standard second is defined as the time taken by cesium -133 atom to make 9192631770 vibrations.
• One second is defined as the 1/86,400 th part of the mean solar day. A particular point in the space is called zenith.
• A solar day is defined as the time interval between the consecutive passages of the sun through the zenith.
• The time taken by the earth to revolve once around the sun is called one year.
.

### Very Short Questions

The duration between any two events is called time. The SI unit of time is second.

One standard second is defined as the time taken by cesium -133 atom to make 9192631770 vibrations.

A solar day is defined as the time interval between the consecutive passages of the sun through the zenith.

One second is defined as the 1/86,400 th part of the mean solar day.

Solution:
We have,
1 year = 365 days = 365 × 24 h = 365 × 24 × 3600 s = 31,536,000 s
Since, the speed of the light in air or vacuum is 3× 108m/s
And distance traveled = speed × time
Therefore, 1 light year = 3 ×108× 31,536,000 s
= 9.4608 × 1015m

I think it's a physicist.

2 min

\begin{align*} \text {Converting into seconds} \\ &= 2\: \text {min} \\ &= 2\times 60\: \text {seconds} \:\:\: [\because 1  \:\text {min} = 60 \: \text {seconds}]\\ &= 120 \: \text {seconds} \\ \end{align*}

3 years

\begin{align*} \text {Converting into seconds} \\ &= 3\: \text {years} \\ &= 3\times 12\: \text {months} \:\:\: [\because 1 \: \text {year} = 12 \: \text {months}]\\ &= 36\: \text {months} \\ &= 36 \times 30\: \text {days} \: \:\:\: [\because 1\: \text {month} = 30 \: \text {days generally}] \\ &= 1080 \: \text {days} \\ &= 1080 \times 24 \: \text {hours} \:\:\: [\because 1\: \text {day} = 24 \: \text {hours}] \\ &= 25920 \: \text {hours} \\ &= 25920\times 60 \: \text {minutes} \:\:\: [\because 1\ \text {hour} = 60 \: \text {minutes}] \\ &=1555200 \:\text {minutes} \\ &=1555200 \times 60\:\:\: [\because 1\: \text {minute} = 60 \: \text {seconds}] \\ &= 93312000\: \text {seconds}\end{align*}

\begin{align*} 1 \: \text {mean solar day} &= 24 \: \text {hours} \:\:\: [\because 1\: \text {mean solar day} = 24\: \text {hours}] \\ &= 24 \: \text {hours} \\ &= 24 \times 60 \: \text {minutes} \: [\because 1 \: \text {hour} = 60 \: \text {minutes}]\\ &= 1440 \:\text {minutes} \\ &= 1440 \times 60\: \text {seconds}
\:\:\: [\because 1\: \text {minute} = 60 \: \text {seconds}] \\ = 86, 400 \: \text {seconds}\\\end{align*}

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• ### A particular point in the space is called ______.

Horizon
Zenith
Astronomical unit
Light year
• ### Which of the follwing is true?

Acceleration = Speed × Time
Acceleration = Speed/Time
Distance Travelled = Speed × Time
Distance Travelled = Speed / Time
• ### The time interval between the consecutive passages of the sun through zenith is ______.

Solar Day
Lunar Day
Blue Moon Day
Astronomical Unit

One Year
6 months
300 days
1 century
• ### Which one of the following is most precise clock?

Mechanical clock
Analog clock
Digital clock
Quantum clock

Meter
Kilometer
Miles
Light year