CHAPTER 3: THE ELECTROMAGNETIC SPECTRUMSECTION 2: WAVES OF THE ELECTROMAGNETIC SPECTRUM

I. What is the Electromagnetic Spectrum?

A. All electromagnetic waves travel at the same speed in a vacuum,

but they have different wavelengths and different frequencies.

1. Visible light = radiation in the wavelengths you can see

a. small portion of electromagnetic radiation is visible light

b. Rest is invisible

2. Different wavelengths for different types of

waves.

3. recall: speed = wavelength x frequency

a. so, as the wavelength decreases, the

frequency increases

a. Waves with the longest wavelengths have the lowest

frequencies

b. amount of energy carried by and EMW increases with

frequency

B. The electromagnetic spectrum- is the complete range of

electromagnetic waves placed in order of increasing frequency.

1. The electromagnetic spectrum is made up of radio waves,

infrared rays, visible light, ultraviolet rays, X-rays, and

gamma rays.

II. Radio Waves

A. Radio Waves- are the electromagnetic waves with the longest

wavelengths and lowest frequencies.

1. Example

a. Broadcast waves: radio and television

b. Microwaves

2.Broadcast waves- these are radio waves with longer

wavelengths.

a. Radio or TV antenna picks up these waves at

certain frequencies

b. Then converted to an electrical signal which is

converted to sound (radio) sound and picture (TV)

B. Microwaves – radio waves with the shortest wavelengths and

the highest frequencies

1. used in cooking, radar, and cellular phone communication

a. Radar = radio detection and ranging

b. Radar – is a system that uses reflected radio waves to

detect objects and measure their distance and speed.

1. distance determined by how long it takes the reflected

waves to return to the device

2. Speed determined by the doppler effect

a. Frequency of reflected waves off of car is different

from the original waves

b. Difference in frequency is the speed

III. Infrared Rays

A. Infrared rays- are electromagnetic waves with

wavelengths shorter than those of radio waves.

1. have more energy than radio waves bc they have a higher

frequency

Ex: the invisible heat (infrared radiation) you feel as burner

warms up before you see the glow

B. Heat lamps:

1. bulbs give off infrared rays

(often called heat rays) and very

little visible light.

B. Infrared Cameras-

1. take pictures using infrared rays instead of light

a. Most objects give off some infrared rays.

2. thermogram- an image that shows regions of different

temperatures in different colors

3. used to see objects in the dark

4. firefighters use infrared cameras to locate fire victims inside a

dark or smoky building.

IV. Visible Light

A. Visible light – electromagnetic waves you can see

1. shorter wavelengths and higher frequencies than infrared rays

a. Red light = longest wavelengths

b. All other colors appear as the wavelengths decrease

c. Violet light = shortest wavelength

d. White light = mixture of many colors

2. use a prism to separate out white light from the sun

a. Waves bend as they enter a new medium

b. Therefore, the prism refracts different wavelengths by different

amounts and separates them into different colors.

1. red light waves refract the least

2. violet light waves refract the most

V. Ultraviolet Rays

A. Ultraviolet rays – electromagnetic waves

with wavelengths just shorter than those of visible light.

1. have higher frequencies than visible light = more energy

2. energy is great enough to damage or kill living cells.

Ex: UV lamps used to kill bacteria on hospitals equipment

3. small doses of UV is beneficial to health: produces vitamin D

(needed for teeth and bones)

4. large doses is dangerous = burn skin,

cause skin cancer, damage eyes

VI. X-Rays-

A. X-Rays- are electromagnetic waves with wavelengths just shorter

than those of ultraviolet rays.

1. have higher frequencies and carry more energy

than UV rays

2. can penetrate most matter

a. Except bone or dense matter = absorbs the x-rays

= does not pass through

3. too much exposure to x-rays can cause cancer

4. lead apron absorbs x-rays preventing them from

reaching your body

VII. Gamma Rays

A. Gamma rays- are the electromagnetic waves with the shortest

wavelengths and highest frequencies

1. most penetrating of all electromagnetic waves

2. can be produced from some radioactive substances and

nuclear reactions

3. used in medicine: kill cancer cells

a. Patient injected with a fluid that emits

gamma rays = forming an image inside the body

4. Explosions of starts are thought to produce gamma rays in the

space

• https://www.youtube.com/watch?v=HPcAWNlVl-8