# Waves and Energy Physics, Grade 8.

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Waves and Energy Physics, Grade 8

Types of Waves Mechanical Waves need matter (medium) to travel through
Electromagnetic Waves can travel through empty space

Mechanical Waves May be longitudinal (compression) Or transverse

Transverse Waves Transverse waves move like a snake going up and down
Light energy moves in transverse waves

Parts of a transverse wave:
As wavelength increases, frequency decreases Wavelength Amplitude Crest Trough How often = Frequency

Compression Waves Compression waves move like a worm, squeezing and releasing Sound energy moves in compression waves

Longitudinal/Compression Waves – energy must move along the medium while traveling forward

Transverse Both Longitudinal
Moves in compressions (pulses) in same direction the wave does Example: sound waves Both have a frequency wavelength, amplitude Both transfer energy from one place to another Wave moves up and down or side to side while traveling forward Example: light waves

Review : Which letter shows the amplitude of the wave at right?
Which letter shows a wavelength of the wave at right? When frequency increases, what happens to the wavelength? b c d a

Electromagnetic Waves

-Identify positive and negative effects of waves on human activities -Compare and contrast the differing frequencies and energy levels of waves in the electromagnetic spectrum

Focus Question What effect does increasing frequency and wavelength have on energy of waves?

Electromagnetic (EM) waves
Light is an electromagnetic wave. EM waves are made up of 2 fields: electric and magnetic.

All EM waves travel at the same speed  the speed of light (c). c = λ f

Types of em waves

Radio Waves Longest wavelengths and lowest frequencies. Lowest energy.
Used to carry sound and picture info to TVs and radios.

Microwaves More energy than radio waves.
Used in microwave OVENS and radar guns. Draw a picture of something that will help you remember microwaves.

This is a microwave OVEN
Note: Microwaves This is a microwave OVEN This is a MICROWAVE Microwaves are used IN microwave ovens to help cook the food. Microwaves are EM waves. Microwave OVENS are NOT EM waves.

Infrared Waves More energy than radio waves and microwaves.
Infrared waves from the sun make you feel warm. Draw a picture of something that will help you remember infrared waves.

Visible Light The kind of light that humans can see.
Includes the colors ROY G BIV. Red has long waves; violet has short waves Draw a picture of something that will remind you of visible light.

Ultraviolet (UV) Light
More energy than visible light Used to kill bacteria on food or surgical instruments. UV rays from the sun can cause sunburn or cancer. Absorbed by the ozone layer. Draw a picture of something that will remind you of Ultraviolet Light.

X-Rays Can be used to take pictures of the inside of your body.
Have large amounts of energy. Draw a picture of something that will remind you of X-Rays

Gamma Rays Carry the most energy of all waves
Highest frequency & shortest wavelength Used to kill cancer cells Given off in nuclear reactions Most dangerous to humans! Draw a picture of something that will remind you of gamma rays.

Look at your spectrum. What happens to the wavelength of EM waves as you move right along the spectrum? The wavelength gets SHORTER as you move up the spectrum. What happens to the frequency of EM waves as you move up the spectrum to the right? The frequency gets HIGHER as you move up the spectrum.

Which waves have the least energy?
Waves on the left have less energy. Radio waves have the least. Which waves have the most energy? Waves on the right have more energy. Gamma rays have the most.

Which waves have a longer wavelength?
Radio or Gamma? Ultraviolet or Infrared? Microwaves or Visible Light? Which waves have a higher frequency? Visible Light or X-Rays? Microwaves or Infrared? Ultraviolet or Visible Light?

Which waves have more energy?
Radio or Gamma? Ultraviolet or Infrared? Microwaves or Visible Light?