High School Physics : Light and Electromagnetic Waves

Study concepts, example questions & explanations for High School Physics

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Example Questions

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Example Question #1 : Light And Electromagnetic Waves

A microwave has a wavelength of . What is the speed of the wave?

Possible Answers:

Correct answer:

Explanation:

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 : Light And Electromagnetic Waves

A microwave has a frequency of . A gamma ray has a frequency of . Which one has a greater speed?

Possible Answers:

They have the same speed

The gamma ray

We need to know the magnitude of the frequencies to solve

The microwave

We need to know the wavelengths to be able to solve

Correct answer:

They have the same speed

Explanation:

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 : Light And Electromagnetic Waves

The frequency of a particular photon of infrared light is . What is the wavelength of the photon?

Possible Answers:

Correct answer:

Explanation:

The relationship between wavelength, frequency, and velocity is:

In this case, because infrared light is a part of the electromagnetic spectrum, we would use  for .

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 : Light And Electromagnetic Waves

An electromagnetic wave travels with a frequency of . What is the wavelength of the wave?

Possible Answers:

Correct answer:

Explanation:

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 : Understanding The Electromagnetic Spectrum

Radio waves and X-rays are both on the electromagnetic spectrum. Which of the following statements is true?

Possible Answers:

Both waves have the same period

Both waves travel at the same speed

None of these are true

Both waves have the same frequency

Both waves have the same wavelength

Correct answer:

Both waves travel at the same speed

Explanation:

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 #2 : Light And Electromagnetic Waves

Why is it that photons can move at the speed of light, but other particles cannot?

Possible Answers:

Photons lack electrical charge

Photons are similar in size to electrons

Photons do not have mass

Photons contain more energy than other particles

Correct answer:

Photons do not have mass

Explanation:

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  to the vertical. If it is moving from air to water, what will be the angle of refraction?

 

Possible Answers:

Correct answer:

Explanation:

For this problem, use Snell's law: .

In this equation,  is the index of refraction and  is the angle of refraction to the vertical. Using the values given in the question, we can find the resultant angle of refraction.

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 . What is the speed of light in this crystal?

Possible Answers:

Correct answer:

Explanation:

The relationship between speed of light and the index of refraction is:

In this formula,  is the speed of light in a vacuum,  is the observed speed of light in the substance, and  is the index of refraction. We are given the speed of light in a vacuum and the index of refraction, allowing us ot solve for the speed of light in the crystal.

Example Question #3 : Understanding Refraction

A new crystal is discovered. The speed of light inside of this crystal is measured to be . What is the index of refraction of the crystal?

Possible Answers:

Correct answer:

Explanation:

The relationship between speed of light and the index of refraction is:

In this formula,  is the speed of light in a vacuum,  is the observed speed of light in the substance, and  is the index of refraction. We given the values for the speed of light in the crystal and the speed of light in a vacuum, allowing us to solve for the index of refraction.

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 #1 : Light And Electromagnetic Waves

A certain gas has an index of refraction of . What is the speed of light in the gas?

Possible Answers:

Correct answer:

Explanation:

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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