Lesson 4 Electromagnetic Spectrum
Objectives- Describe what the electromagnetic spectrum is and how it is arranged;
describe important features of each of the electromagnetic waves.
Electromagnetic waves are transverse waves that do not require matter (a
medium) to travel. That means these waves can travel through space. These waves
allow for many different types of communication and for the energy from the sun to reach
earth. Without the sun’s energy, life could not exist.
The electromagnetic spectrum shows all the different kinds of electromagnetic
waves. (See page 540). All of the different types of electromagnetic waves travel at the
same speed- 300,000km/sec or 186,000miles/hour. However each has a different
wavelength and frequency. The spectrum is arranged so the waves on the left side have
the longest wavelengths and the lowest frequencies. As you go to the right, each wave’s
frequency increases while its wavelength decreases. Also, as you go the right, each
wave has an increasing amount of photons. Photons are a way of describing how much
energy the waves have.
The first group on the spectrum is the radio waves. Each type has its own
frequency and wavelength. When you change the station on the radio, you are detecting
different waves. The word modulation means to change radio waves. AM stations each
have a different amplitude (amplitude modulation) while FM stations have different
frequencies (frequency modulation). Microwaves are a type of radio wave. They have
enough photon energy to cause the water in food to begin to move more quickly, raising
the temperature and causing the food to cook.
We can not see infrared radiation but we know it exists. We feel it as heat. By
detecting infrared radiation with special viewing aids, we can do things such as detect
tumors (they give off more heat), find heat lose in homes, and used by military and
police to find people.
Visible light makes up the next part of the spectrum. Visible light is actually
made up of 6 different colors of light- red, orange, yellow, green, blue, and violet. It is a
very small part of the spectrum. All the different parts of the visible spectrum together
are called white light. By changing the ratio wavelengths we can get lights that produce
different colors and are useful for things like growing plants.
Ultraviolet light (UV) radiation is next on the spectrum. Ultraviolet light that
comes from the sun helps your body to produce vitamin D. It has enough photon energy
to allow it to be used by health care professionals to kill harmful bacteria. However, to
much ultraviolet light can cause skin cancer. The ozone layer in the atmosphere helps
to keep out some of the sun’s UV radiation.
Next on the spectrum are X-rays. X-rays have very short wavelengths and high
frequencies. X-rays are absorbed by objects that have a high a density like metals and
bones. These also have a large amount of photon energy. Overexposure to these can
be harmful. For this reason, health care professionals who work with X-rays leave the
room when taking X-rays and they lay a lead vest over the person who they are taking
the X-rays of.
The last type of waves shown on the electromagnetic spectrum is gamma rays.
Gamma Rays have very high levels of photon energy. These waves are used to treat
some forms of cancer in radiation therapy. However these waves do not distinguish
between “good and bad” cells and can kill many healthy cells while killing the cancerous
cells.
Questions Lessons 1
Define electromagnetic wave.
How fast do electromagnetic waves travel?
How is each wave different from the others on the electromagnetic spectrum?
What is a photon?
When you change FM radio stations, how is each stations wave different?
How is ultraviolet light useful? Harmful?
How are gamma rays useful?
Why do people need to protect themselves from overexposure to
X-rays?
Bonus questions
Which travel farther, AM or FM radio waves? Why?
What are the different parts of the visible light? How is each different?