The Electromagnetic Spectrum

I. Characteristics of EM Waves The EM spectrum is arranged from long to short wavelengths and from low to high frequency. The entire range of EM waves is the EM spectrum. Examples radio waves: low frequency & long wavelengths Microwaves infrared waves Visible light Ultraviolet rays X-rays gamma rays: high frequency & short wavelengths

How Big Are EM Waves?

II. Radio Waves Radio waves cover a large part of the EM spectrum. A radio station converts sound into an electric current. The current produces radio waves that are sent out in all directions. A radio receives the waves and converts them to electric current, which is then converted to sound.

III. What is the difference between AM and FM radio? If a radio station modulates (changes) the frequency of a wave, it is FM radio. This is known as frequency modulation. If a radio station modulates the amplitude of a wave, it is AM radio. This is known as amplitude modulation. FM waves have a shorter wavelength than AM waves, and are less affected by electrical noise, so the stations sound better. AM waves have a longer wavelength than FM waves. They can also travel very far. But they don’t sound as good as FM waves.

IV. TV and Radio Television signals are carried on radio waves. i. The waves have shorter wavelengths and higher frequency than those of radio stations. Both AM and FM signals are used for television signals.

V. Microwaves Microwaves have shorter wavelengths and higher frequencies than radio waves. The wavelengths are between 1mm and 30 cm. Microwaves are produced in a microwave oven. These waves bounce off a metal fan and penetrate several centimeters into the food. This causes the water molecules inside the food to rotate, which causes the food to get hotter.

VI. Microwaves and Radar Microwaves are also used in radar (radio detection and ranging). The radar gun sends out microwaves that reflect off the car and bounce back to the gun. This can tell the speed of a car. Radar can also be used to watch airplanes and help ships navigate at night.

VII. Infrared Waves Infrared waves have even shorter wavelengths and higher frequencies, even shorter than microwaves. You are warmed by the sun’s infrared waves. They cause the particles in your skin to vibrate faster, which heats you up. But all objects give off infrared waves. The hotter something is, the more infrared waves there are, even though you can’t see them.

d. Where is the heat on this person’s body d. Where is the heat on this person’s body? Look at the infrared waves to see.

VIII. Visible Light Visible light is the narrow range of wavelengths in the EM spectrum that humans can see with their eyes. Visible light from the sun is known as white light. We see the different wavelengths of visible light as color. The longest wavelengths are red, and the shortest wavelengths are violet. You can remember the colors of visible light in order from longest wavelength to shortest by remembering ROY G. BIV. This name stands for Red, orange, yellow, green, blue, indigo and violet.

IX. Ultraviolet Light Ultraviolet light (UV) is another type of EM wave produced by the sun. They have short wavelengths and higher frequencies than visible light waves. There are good and bad effects of UV light on human bodies.

Good or Bad? d. Bad Effects of UV light e. Good Effects of UV light Skin Cancer Wrinkles Damage to eyes Kills bacteria Produces vitamin D

X. X-Rays and Gamma Rays X-rays and gamma rays have the shortest wavelengths and highest frequencies of all EM waves. X-rays can pass through materials, so they are helpful to doctors. But too many X-rays can kill living cells. Gamma rays can also penetrate materials easily. They are used to treat some forms of cancer. They can kill the bad cells, but they can kill some healthy cells too. Gamma rays are also used to kill harmful bacteria in food. It is safe to eat if it has been treated with gamma rays.

Quickie Quiz Which radio waves have a stronger signal, AM or FM waves?

Quickie Quiz Which is not a type of electromagnetic wave? X rays Gamma rays Visible light Sound waves

Quickie Quiz Which is not a property of an electromagnetic wave? Needs a medium Magnetic field Doesn’t need a medium Electric field

Quickie Quiz Which electromagnetic wave has the shortest wavelength and highest frequency? Radio waves Infrared waves Gamma rays Ultraviolet light

Quickie Quiz What is one good thing about ultraviolet light?

Quickie Quiz Which visible light color has the largest wavelength and lowest frequency? Yellow Purple Green Red

Quickie Quiz Which one is NOT something microwaves do? Produces vitamin D Detect car speed Help ships navigate at night Watch airplanes