Units and Measurement

Question : 29 of 33

Marks: +1, -0

A laser is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?

Solution:

Here,

t = 2.56\,\text{s}

velocity of laser light in vacuum,

c = 3 \times 10^{8}\,\text{m/s}

The radius of lunar orbit is the distance of moon from earth. Let it be

x

x = \frac{c \times t}{2}

\therefore x = \frac{3 \times 10^{8} \times 2.56}{2}

= 3.84 \times 10^{8}\,\text{m}

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