High School Physics : Light and Electromagnetic Waves
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Example Questions
Example Question #1 : Understanding The Electromagnetic Spectrum
A microwave has a wavelength of 
Since a microwave is a part of the electromagnetic spectrum, its velocity will be equal to the speed of light:
Any wave on the electromagnetic spectrum will have the same velocity, though their wavelengths and frequencies will vary, defining their individual characteristics.
Example Question #2 : Understanding The Electromagnetic Spectrum
A microwave has a frequency of 
We need to know the wavelengths to be able to solve
They have the same speed
We need to know the magnitude of the frequencies to solve
The gamma ray
The microwave
They have the same speed
Both of these waves are on the electromagnetic spectrum. Any wave on the spectrum will have the same speed, the speed of light.
Radio waves, microwaves, infrared waves, visible light, ultraviolet light, and gamma rays are all on the spectrum. They all have the same ultimate speed, but vary in their wavelengths, frequencies, and energy levels.
Example Question #3 : Understanding The Electromagnetic Spectrum
The frequency of a particular photon of infrared light is 
The relationship between wavelength, frequency, and velocity is:
In this case, because infrared light is a part of the electromagnetic spectrum, we would use 
We are given the speed of light and the frequency of the photon. Using these values, we can solve for the wavelength.
Example Question #4 : Understanding The Electromagnetic Spectrum
An electromagnetic wave travels with a frequency of 
The relationship between velocity, frequency, and wavelength of a waveform is given by the formula:
In this case, we are dealing with an electromagnetic wave. All electromagnetic waves travel at the same velocity: the speed of light.
Using this value and the given frequency of the wave, we can solve for the wavelength.
Wavelength is traditionally reported in nanometers, corresponding to 
Example Question #1 : Light And Electromagnetic Waves
Radio waves and X-rays are both on the electromagnetic spectrum. Which of the following statements is true?
Both waves have the same period
Both waves have the same wavelength
Both waves travel at the same speed
None of these are true
Both waves have the same frequency
Both waves travel at the same speed
Any wave on the electromagnetic spectrum will travel at the same constant speed, the speed of light. Each type of wave is determined by changes in the frequency, wavelength, and energy, but these factors always reflect a constant velocity. The types of waves in the electromagnetic spectrum are radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. Radio waves will have the largest wavelength, smallest frequency, and lowest energy. Gamma rays will have the smallest wavelength, highest frequency, and greatest energy.
The inverse relationship between frequency and wavelength means that the velocity can remain constant.
Example Question #1 : Light And Electromagnetic Waves
Why is it that photons can move at the speed of light, but other particles cannot?
Photons contain more energy than other particles
Photons lack electrical charge
Photons do not have mass
Photons are similar in size to electrons
Photons do not have mass
Photons can move at the speed of light because they have no mass. Anything with mass can not be accelerated to the speed of light—it takes an infinite amount of energy to do so. We can get very close, but never exactly there.
Example Question #1 : Understanding Refraction
A ray of light strikes the surface of a pond at an angle of 
For this problem, use Snell's law: 
In this equation, 
Take the arcsin of both sides to find the value of 
Example Question #2 : Understanding Refraction
A new crystal is discovered with an index of refraction of 
The relationship between speed of light and the index of refraction is:
In this formula, 
Example Question #3 : Understanding Refraction
A new crystal is discovered. The speed of light inside of this crystal is measured to be 
The relationship between speed of light and the index of refraction is:
In this formula, 
Plug in our given values and solve.
Note that the index of refraction is a ratio of two velocities, and therefore has no units.
Example Question #4 : Understanding Refraction
A certain gas has an index of refraction of 
The index of refraction is defined as the relationship between the speed of light in a vacuum over the speed of light in the gas/liquid/solid.
We know the index of refraction of the gas, and the speed of light in a vacuum. Using these values, we can solve for the speed of light in the gas.
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