Name____________________________________________ Period _______________

Electromagnetic wave worksheet

On a separate sheet of paper, answer the following questions. Staple your answers to this sheet.

1. What kind of wave is a light wave?

A light wave is a transverse wave. It is also an electromagnetic wave.

2. What is a medium? Give some examples.

A medium is a substance that longitudinal waves (also known as compressional waves) travel through. The longitudinal wave compresses and rarifies the medium as the wave transfers energy from one place to another.

Some examples of mediums are air, water, wood and metal. When I speak to you, my voice creates sound waves by compressing and rarifying the air. This sound wave carries energy to your eardrum. The compressions and rarifications cause your eardrum to vibrate at the same pattern as the vibrations that left my vocal cords. That is how you hear what I say. This is easier to understand if you look at the cone of a speaker. You can watch it vibrate, and imagine the compressions in creates in the air.

3. What is a vacuum?

A vacuum is a lack of a medium. A vacuum is “nothingness”. Space is a vacuum. There is no air on the Moon, so if you were standing on the Moon, you would be in a vacuum.

4. Can sound travel through a vacuum?

No. Sound is a longitudinal wave (also known as a compressional wave). It needs a medium to compress and rarify in order for the wave to carry energy from one place to another. Although we can see the Sun, we can not hear the Sun. That is because a vacuum exists in between Earth and the Sun. If sound could travel through a vacuum, the Sun would be deafeningly loud. We are lucky sound doesn’t travel through vacuums.

5. Can light travel through a vacuum?

Yes. We know this because we can see the Sun, and other objects in space.

6. Is light the only electromagnetic wave? If not, give some other examples.

No. Other electromagnetic waves include radio waves, infrared waves, ultraviolet waves, microwaves, x-rays and gamma rays.

7. What is the wavelength range for the FM radio band (88 MHz – 108 MHz)?

(Don’t let the lengthiness of my response scare you. I’m just spelling it out in great detail. The actual solution I expect on a test is only about 2 lines long.)

Wavelength is a distance. It is the distance between a point on a wave, and the next identical point on a wave. Hz is a frequency. It means 1/second. Frequency is the inverse of period, which is the amount of time it takes a wave to move one wavelength. M means “mega”, which means million. So replace mega with .

To solve this problem, start with the formula you are already familiar with:

Before you even set foot in a Physics class, you knew this formula. I’ve reminded you many times in class by asking you “If you travel at 60 miles per hour for 2 hours, how far have you gone?” All of you confidently answer “120 miles”, which is what you get if you multiply your velocity by your time, demonstrating that you already knew this formula.

Since wavelength is a distance, we can replace it with the Greek letter Lambda, λ, which is the variable we use to represent wavelength. And since time = 1/frequency, we can replace t with 1/f. Since the velocity of any electromagnetic wave is the speed of light, and we use the letter c to represent the speed of light, we can replace v with c. Remember, . Then we are ready to solve for wavelength with the data from the question.

For 88 MHz

And for 108 MHz

So the wavelength range for the FM radio band is 2.78 m to 3.4 m.

8. What is the frequency of an electromagnetic wave if it has a wavelength of 1.0 km? In what part of the electromagnetic spectrum is this wave? (Refer to p. 387 of Hewitt).

(

In the following solution, I again start out with the formula we are all familiar with, d=vt, and modify it to fit this problem. But you could always start with f=v/d if you want, to make your solution simpler.)

Looking at p. 387 of Hewitt, I can see that this is a radio wave.

9. Shortwave radio is broadcast between 3.50 and 29.7 MHz. To what range of wavelengths does this correspond? Why do you suppose this part of the spectrum is called shortwave radio?

So the rage of wavelengths is 10 m to 86 m.

Since radio waves can be as long as 1000 km, these are pretty short for radio waves. That’s why they call them shortwave radio.

10. A burst is a brief flash or pulse of light or other electromagnetic wave. Gamma-ray bursters are objects in the universe that emit pulses of gamma rays with high energies. The frequency of the most energetic bursts has been measured at around . What is the wavelength of these gamma rays?

11. The portion of the visible spectrum that appears brightest to the human eye is around 500 nm in wavelength, which corresponds to yellow-green. What is the frequency of 560 nm light?

12. What is the frequency of highly energetic ultraviolet radiation that has a wavelength of 125 nm?