Textbook Problem

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Speed of Light

The Sun is $\text{1}\text{.5 }\times {\text{ 10}}^{\text{8}}\text{km}$ from Earth. How long does it take light to travel from the Sun to Earth?

Interpretation Introduction

Interpretation:

The time taken by light to travel from the Sun to the Earth is to be determined.

Concept Introduction:

Electromagnetic radiation with a certain wavelength is called light.

Electromagnetic radiation is a type of energy that surrounds us. It may lie in the visible region.

Speed is the distance travelled per unit time.

The relation between speed, time and distance is as follows:

$\text{Time}=\frac{\text{Distance}}{\text{Speed}}$

Here, distance is in meters, speed is in $\text{meter/second}$ and time is in seconds.

Explanation of Solution

Given information: The distance of the Sun from Earth is $1.5\times {10}^8\text{km}$ and the speed of light is $3\times {10}^8\text{m/s}$.

First, the relationship between kilometer and meter is as follows:

$\begin{array}{l}1\text{km}=1\times {10}^3\text{m}\\ 1.5\times {10}^8\text{km}=\frac{1.5\times {10}^8\cancel{\text{km}}\times \text{1}\times {\text{10}}^3\text{m}}{1\cancel{\text{km}}}\\ =1.5\times {10}^8\text{m}\end{array}$

Also, the relationship between minute and second is as follows:

$\begin{array}{c}1\text{min}\text{=}\text{60 s}\\ \text{3}\times {\text{10}}^8\text{m/s}\text{= }\frac{\text{3}}{}\end{array}$