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POGIL: The Electromagnetic Spectrum (ANSWER ALL QUESTIONS IN YOUR NOTEBOOK)
We have learned that light is a wave, but what exactly is “waving”? Light is an electromagnetic wave; it is
called this because it consists of electric and magnetic force fields. If you’ve ever played with magnets or
charged objects, you can feel the magnetic or electric force field when the magnets or charges attract or repel. In
this POGIL we will look at the classes of electromagnetic waves that comprise the electromagnetic spectrum.
Electromagnetic Waves
The diagram at right shows a representation of
an electromagnetic wave.
The arrows labeled “electric field” are electric force fields; they are what push like charges apart and pull unlike
charges together. The arrows labeled “magnetic field” are magnetic force fields; they are what push like
magnetic poles apart and pull unlike magnetic poles together.
1. In a water wave, water vibrates to produce a wave pattern. In waves on a rope, the parts of the rope vibrate
to produce the wave pattern. What is vibrating in an electromagnetic wave?
2. Are electromagnetic waves a type of transverse wave or a type of longitudinal wave? Explain your answer.
The Electromagnetic Spectrum
Recall that light waves are electromagnetic waves that can have different frequencies, wavelengths, and
energies. These properties of light waves determine the color that we perceive. The color spectrum (ROYGBIV)
is simply the order of color from lowest frequency to highest frequency. But there are classes of electromagnetic
waves above and below these frequencies that our eyes do not detect.
There are seven different classes of electromagnetic waves: radio waves, microwaves, infrared, visible light,
ultraviolet, X-rays, and gamma rays. Each class can be imagined with the same representation shown in the
diagram above. However, each class has a different range of frequencies, wavelengths, and energies.
•
•
1 Hz
All electromagnetic waves have the same speed of 300,000,000 m/s (equal to approximately 186,000 miles
per second). In scientific notation, this is written as 3×108 m/s (a “3” followed by eight zeros).
The range of frequencies for each class is shown in the chart below. Note that the frequencies are shown on a
logarithmic scale, meaning that each increment represents another factor of 10 instead of an addition of 10 Hz.
102 Hz
104 Hz
radio waves
106 Hz
108 Hz
1010 Hz 1012 Hz 1014 Hz 1016 Hz 1018 Hz 1020 Hz 1022 Hz
microwaves
infrared
ultraviolet
visible
light
AM radio
FM radio, TV
X-rays
gamma rays
3. List the classes of electromagnetic waves in order from LOWEST frequency to HIGHEST frequency.
4. List the classes of electromagnetic waves in order from LOWEST speed to HIGHEST speed.
5. Recall that for any wave,
𝑤𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑=𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 ×𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ.
With this in mind, list the classes of electromagnetic waves in order from SHORTEST wavelength to
LONGEST wavelength.
6. The energy of an electromagnetic wave is directly proportional to its frequency. List the seven classes of
electromagnetic waves in order from LOWEST energy to HIGHEST energy.
7. In what sense is the electromagnetic spectrum just a continuation of the color spectrum?
8. How are infrared, X-rays, gamma rays, radio waves, ultraviolet, and microwaves:
(a) different from light?
(b) the same as light?
Problems
9. A radio station broadcasts its signal with electromagnetic waves at a frequency of 108 Hz.
(a) Is this an AM or FM station?
(b) What is the wavelength of the electromagnetic waves sent out by the station?
10. An electromagnetic wave has a frequency of 5×1014 Hz.
(a) To what class of the electromagnetic spectrum does this wave belong?
(b) What is its wavelength?
11. The distance between the Earth and Sun is approximately 150 billion (1.5×1011) meters.
(a) How much time in seconds does it take light to travel from the Sun to the Earth?
(b) How much time does it take an X-ray to travel from the Sun to the Earth?