Calculating Light Speed Worksheet

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Conversions and Calculations Using Light Speed

Everyone knows that light travels fast. In fact, current physical laws state that nothing in the universe should be capable of moving faster than the speed of light. But exactly how fast is this? How do we know?

The first attempts to measure the speed of light were the same way the speed of any other object is measured, distance traveled over time. The problem with this is that light is so fast it travels between points on Earth seemingly instantaneously. The first real calculations of light speed came from the shadows of Jupiter’s moons. When Earth was closest to Jupiter, the orbit of Io seemed ahead of schedule and vice versa. More accurate measurements after that came from rotating mirror systems. The most accurate and modern measurements come from atomic clocks. You will be making the same measurements, but your job will be much easier as you get to work with more known values.

Known Values and equations:

V = d / t (where V = velocity, d = distance, and t = time)

distance of Earth to Sun = 149,597,870.7 km

Time it takes light to travel from the Sun to Earth = ~ 8 minutes and 19 seconds

Calculate the following:

1.) Speed of light:

2.) Light year:

3.) Time for light to travel from Earth to mars (avg. distance of 225 million km):

Now that you have calculated the velocity of light, you are able to make more calculations based on it. As you may know, there is more than one type of light. Each type of light has a different range of frequency and a different range of wavelength. Because of this, the speed of light can be broken down into a slightly different equation:

V = f * (where f = frequency and = wavelength)

frequency = waves per second

wavelength = length of individual waves (duhh….)

For these problems, calculate values with the actual speed of light: 299,792,458 m / s

4.) Wavelengths of visible light: (frequencies of 430 THz to 790 THz)

5.) Frequency of atomic hydrogen hyperfine transition:

= 21 cm

6.) Calculate the frequencies corresponding to each wavelength provided:

a - 3 m:

b - 500 nm:

c - 30 pm:

7.) Calculate the wavelengths corresponding to each frequency provided:

a - 50 MHz:

b - 30 kHz:

c - 200 GHz:

Metric prefixes