## Light - Behavior and Principles

**1.** The average distance between Earth and the Sun is 150,000,000 km. How long does light take to reach Earth? (Considering c = 300,000 km / s).

*The first step is to understand the displacement of light. How ç is a constant velocity, the movement must be uniform, ie:*

*With this, simply replace the values given in the exercise:*

*We can still express this time in minutes:*

*Therefore, the light takes approximately 8 minutes and 20 seconds to travel from the sun to the earth.*

**2.** When the space missions reached the moon mirrors were left on its surface so that experiments could be done with them. Suppose that, using one of these mirrors, you want to find out the distance between the Earth and the Moon. *laser* which is captured after 2.54 seconds. Disregarding the movements of the earth and the moon, and using c = 300,000 km / s, how far is our planet from its natural satellite?

*As in the previous exercise, the light describes a uniform movement, thus:*

*The time required for the laser to reach the receivers is equivalent to the round trip of light, so we need to use half this time, ie 1.27 seconds:*

**3.** Light year is the measure of distance used in astronomy that refers to the space traveled by light during a terrestrial year. Considering c = 300,000 km / s and 1 year = 365.25 days, how many kilometers is one light year?

*We need to convert the unit of time to seconds and for that we need to know that:*

*1 minute = 60 seconds*

*1 hour = 60 minutes = 3600 seconds*

*1 day = 24 hours* = *1440 minutes = 86400 seconds*

*1 year = 8766 hours = 525960 minutes = 31557600 seconds*