ELECTROMAGNETIC SPECTRUM - NASA

E-Activity 10

Copy and complete the following sentences.
1. The case of a microwave oven is made of _____ this ____microwaves.
2. Food contains ____molecules. These _____microwaves and become hot.
3. The food is put into containers made of _____, _____ or _____. These materials allow microwaves to pass through them very easily. We say that they _____ the microwaves.
4. We use a _____ dish to collect enough microwaves for a strong signal. This _____ the microwaves on to an aerial.
5. The aerial transfer’s energy from the microwaves as an ______signal.
6. X-rays can pass easily through skin and flesh but not through _____ or _____.
7. Photographic _____ absorbs any X-rays that fall on it. These parts of the film then go _____ when the film is developed.
8. Gamma radiation can kill living _____.
9. It is used to kill harmful _____ or _____ cells inside people’s bodies.
10. Radiation from the sun, or from a sun bed, can give pale skins a _____. But it can also damage skin cells and cause skin _____. These things happen because of _____ radiation.
11. Some substances _____ ultraviolet radiation and use the energy to produce _____. We say that these substances are _____.
12. Toasters and grills cook food using _____ radiation. Foods become hot when they _____ this radiation.
13. Metal things _____ microwaves, even if they are full of small holes. Some microwaves can pass easily through the Earth’s _____. These microwaves are used to carry information to and from _____.
14. Infrared rays are used to control a _____ set or a _____ player, and to send telephone messages along _____ fibers.
15. In microwave ovens, the microwaves are strongly absorbed by _____molecules in food. The energy from the microwaves makes the food_____.

E-Activity 9

1. What substance will radio waves pass through easily?
2. What happens when radio waves are absorbed by an aerial?
3. Why can’t you send a radio message to or from a submarine?
4. Why is it useful to be able to reflect long wavelength radio waves?
5. What is the wavelength of these radio waves?
6. What wavelengths of microwaves are used for satellite television? And why are these wavelengths used?
7. How is your instruction carried to the television set or video player?
8. Why must you point the remote control at the television set or video player?
9. Doctors can use X-rays to see whether your lungs are healthy. How do they know if there is diseased tissue in your lungs?
10. Why can X-rays and gamma rays cause cancer?

Gamma Rays

Gamma rays are electromagnetic waves emitted by radioactive nuclei. They are also released during nuclear reactions.
Wavelengths of gamma rays range from about 10-10 m to less than 10-14 m.
They are very penetrating and cause serious damage when absorbed by living tissues.

X-Rays

X-rays are electromagnetic waves with wavelengths ranging from about 10-8 m (10 nm) down to 10-13 m (10-4 nm).
X-rays are used as a diagnostic tool in medicine and dentistry.
If you have experienced traveling by air, you would have noticed that your luggage are inspected by the security officer present using x-rays.

Ultra-Violet Radiation

Ultra-violet radiation is the radiation beyond the violet end of the visible spectrum.(wavelengths range from 10-8 to 10-7 m)
The main source of ultra-violet radiation is sunlight and it is this radiation which gives rise to suntans.
Ultra-violet radiation from the sun also stimulates our body to produce vitamin D, which we need for healthy bones.
However overexposure to ultra-violet radiation can cause skin-cancer and damage to the retina.
Ultra violet radiation also kills bacteria and viruses. Thus it is used to sterilize hospital operating rooms and surgical instruments.
Low intensity ultra-violet lamps are sometimes placed above grocery meat counters to reduce spoilage.

Infra-Red Radiation

The name infra-red means beyond red. There are waves just beyond the red end of the visible spectrum. In fact, all objects with temperatures above 0 K emit infra-red radiation.
When objects absorb infra-red radiation, they become hotter. This property of infra-red radiation is used to provide heat treatment for various illnesses.
We are not able to see in the dark because our eyes are sensitive only to the visible part of the electromagnetic spectrum. However, an infra-red camera, with special photographic films which are sensitive to infra-red radiation, can be used to take pictures in the dark without using a flashlight.
Infra-red radiation can also be used in intruder alarms. An intruder would unknowingly block the rays and set off an alarm.
One popular use of infra-red radiation today are the remote control devices for many electrical appliance via infra-red radiation which is produced by light emitting diodes (LEDs) inside the unit.

Microwaves

Microwaves are very similar to UHF radio waves. They have wavelengths of a few centimeters.
Microwaves are produced by special electronic devices such as the klystron tube.
Microwaves are used to transmit television signals and are also used in telecommunications.
Due to its short wavelength, relative to radio waves, the microwave signal can travel in a straight line without losing much of its energy.
Radar systems use microwaves to find the direction and distance of objects which reflect the microwaves back to a large receiving aerial mounted near the transmitter.
Nowadays, another common use of microwaves is in microwave ovens.

Radio Waves

Radio waves have the longest wavelengths of the waves in the electromagnetic spectrum. The wavelengths range from several hundred meters (long wave, LW) to a few centimeters (ultra high frequency, UHF).
They are used in radio and television communication to transmit sound and picture information over long distances.

ELECTROMAGNETIC SPECTRUM

Electromagnetic waves

All electromagnetic waves have certain fundamental properties in common. They basically differ from each other in their wavelengths and in the effects produced.
Properties of Electromagnetic Waves
An electromagnetic wave is produced by the simultaneous vibration of electric and magnetic fields.
Features common to all the electromagnetic waves include the following:
They transfer energy from one place to another.
They are transverse waves.
They can travel through a vacuum.
They travel through a vacuum at 300 000 000 meters per second (3 x 108 m/s). This speed is commonly known as the speed of light.
They all show wave properties like reflection and refraction.
They obey the wave equation  = ƒ 
Application of Electromagnetic Waves
Electromagnetic waves have wavelengths ranging from several kilometers (in the case of radio waves) to less than a picometer(10-12 m) (in the case of gamma rays).
The shorter the wavelength, the higher the frequency.
As the frequency gets higher, the energy also increases. This causes different electromagnetic waves to have different properties and applications.

E-Activity 8

1. What is the velocity of a wave of frequency 600 Hz and wavelength 0.5m?
2. What is the frequency of a wave of wavelength 0.9m and velocity 300 ms-1 ?
3. What is the wavelength of a wave of velocity 300 ms-1 and frequency 1000 Hz?
4. A source of frequency 500 Hz emits waves of wavelength 0.2 m. how long does it take the waves to travel 400m?
5. A wave of frequency 500 Hz travels between two points P and Q with a velocity of 300 ms-1 . How many wavelengths are there in PQ if the length of PQ is 600 m?
6. To understand the wave motion of a transverse wave or a longitudinal wave, we have to examine how the wave particles vibrate as the wave propagates through the medium.
7. Surf the Internet to locate information on transverse and longitudinal waves. Choose the web sites that show animation of the waves. Write down the similarities and the differences of the two types of waves and give examples of each.

Waves

There are different kinds of waves. All waves have one thing in common: they transfer energy from one place to another.
• A wave is a phenomenon in which energy is transferred through vibrations. The wave carries energy away from the wave source. You can see the effect of rope waves if you fix one end of a rope by tying it round a rod and move the other end up and down. A series of crests and troughs can be seen to pass along the rope. Each section of the rope is set into an up-and-down motion by the previous section as the wave passes along the rope.
• The rope is the medium through which the wave propagates. Note that the particles in the rope itself do not move forward with the wave.
• A similar effect is obtained with water waves. A small cork on the water surface will bob up and down (or vibrate) as the wave passes, but will not travel forward with the wave. In this case, water is the medium through which the energy is transmitted.
Types of Waves
1. Transverse waves
2. Longitudinal waves
Transverse waves• Water waves and rope waves are examples of transverse waves. Transverse waves are waves which travel in a direction perpendicular to the direction of the vibrations. If you move the end of a slinky coil from side to side, transverse waves are set up. Light waves and other electromagnetic waves are also transverse waves.
At home you produce transverse waves when you shake the dust from a blanket or rug. Watch closely the motion of your hand, flipping the edge of your blanket, and the waves that are produced.
Longitudinal waves
• Another type of wave is the longitudinal wave. Longitudinal waves travel in a direction parallel to the direction of vibrations.
• If a slinky coil is pushed and pulled at one end, longitudinal waves are set up. Watch the way the compression travels along the coil. The compressed coils themselves do not travel. They just vibrate forward and back. Sound waves are examples of longitudinal waves.
Wave Terms• Some of the terms and quantities used to describe transverse wave motion are as follows:
1. The high points are called crests or peaks while the low points are called troughs.
2. The amplitude is the maximum displacement from the rest position. It is the height of a crest or depth of a trough measured from the normal undisturbed position.
3. The wavelength, l, is the distance between two successive crests or two successive troughs. It is also equal to the distance between any two identical points on successive waves, for example points A and B, and points C and D in figure
4. The frequency, ƒ, is the number of crests (or troughs) that pass a point per second. This is equivalent to the number of complete waves generated per second. Frequency is measured in hertz (Hz). A frequency of 1 hertz means that one wave cycle or one oscillation is completed per second.
5. The period, T, is the time taken to generate one complete wave. It is also the time taken for the crests, or any given point on the wave, to move a distance of one wavelength. T = 1 / ƒ
6. The speed, n, of the wave is the distance moved by a wave in one second. Since the wave crest travels a distance of one wavelength in one period, the wave speed, n = l/T or n = ƒ l
7. In longitudinal waves, the part where the particles of matter are closest together is called the compression. The part where the particles are spread apart is the rarefaction.

Three Laws of Motion