Find the microwave in the Figure 1.1. A microwave is an electromagnetic wave with a relatively long wavelength and low frequency. Microwaves are often classified as radio waves, but they have higher frequencies than other radio waves. With higher frequencies, they also have more energy. Thats why microwaves are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar. These uses are described below. Click image to the left or use the URL below. URL:
Cell phone signals are carried through the air as microwaves. You can see how this works in the Figure 1.2. A cell phone encodes the sounds of the callers voice in microwaves by changing the frequency of the waves. This is called frequency modulation. The encoded microwaves are then sent from the phone through the air to a cell tower. From the cell tower, the waves travel to a switching center. From there they go to another cell tower and from the tower to the receiver of the person being called. The receiver changes the encoded microwaves back to sounds. Q: Cell towers reach high above the ground. Why do you think such tall towers are used? A: Microwaves can be interrupted by buildings and other obstructions, so cell towers must be placed high above the ground to prevent the interruption of cell phone signals.
Radar stands for radio detection and ranging. In police radar, a radar gun sends out short bursts of microwaves. The microwaves reflect back from oncoming vehicles and are detected by a receiver in the radar gun. The frequency of the reflected waves is used to compute the speed of the vehicles. Radar is also used for tracking storms, detecting air traffic, and other purposes. Q: How are reflected microwaves used to determine the speed of oncoming cars (see Figure 1.3)? A: As the car approaches the radar gun, the reflected microwaves get bunched up in front of the car. Therefore, the waves the receiver detects have a higher frequency than they would if they were being reflected from a stationary object. The faster the car is moving, the greater the increase in the frequency of the waves. This is an example of the Doppler effect, which can also occur with sound waves.
defining electromagnetic waves
Electromagnetic waves carry energy through matter or space as vibrating electric and magnetic fields. Electromag- netic waves have a wide range of wavelengths and frequencies. The complete range is called the electromagnetic spectrum. The Figure 1.1 shows all the waves of the spectrum. The waves used in radar guns are microwaves.
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electromagnetic waves vary in their
a) speed. b) frequency. c) wavelength. --> d) two of the above
the electromagnetic spectrum is defined as the full range of colors of visible light.
a. true --> b. false
microwaves have lower frequencies than other radio waves.
a. true --> b. false
microwaves are used for
a) heating food. b) cell phone transmissions. c) radar. --> d) all of the above
microwave signals can be interrupted by buildings and other obstructions.
--> a. true b. false
radar is used for
a) computing the speed of vehicles. b) detecting air traffic. c) tracking storms. --> d) all of the above
No diagram questions associated with this lesson