Electromagnetic Spectrum

The properties of EM waves change as the frequency or wavelength changes. They are split into 7 basic types:

1. Radio Waves

2. Micro Waves

3. Infrared

4. Visible Light

5. Ultra Violet

6. X-Rays

7. Gamma Rays

(Ranked in increasing danger).

EM waves at the top end of the spectrum (high frequency, small wavelength) tend to be able to pass through material, whilst those nearer to the middle are absorbed.

Acronym for remembering the waves: Guest (Gamma Rays) Experience (X-rays) Unusual (Ultraviolet) Vibrations (Visible Light) In (Infrared) My (Microwaves) Room (Radio Waves).

All Em waves travel at exactly the same speed as light in vacuum, and pretty much the same speed as light in other media like glass & water. The way any EM wave is absorbed, transmitted, or reflected by any given substance depends entirely on its wavelength.

When any EM radiation is absorbed, it can cause 2 effects:

1. Heating

2. The creation of a tiny alternating current with the same frequency as the radiation.

Radio Waves:

Uses: communication, broadcasting, radar

Effects on living tissue: probably none

Microwaves:

Effects on Living tissue: heating of water in tissues can cause a “cold burn”

They have 2 main uses: Cooking and satellite transmissions

However, cooking uses a microwave frequency that is readily absorbed by water, and satellite transmissions use a microwave frequency that passes easily through the Earth’s atmosphere.

How does a microwave work?

The microwaves easily pass into the food and are absorbed by the water molecules and turn into heat inside the food.

Infrared:

Effects on living tissues: Causes burning of tissues

Uses: radiant heaters, grills, remote controls, thermal imaging (night vision)

How does night vision/thermal imaging work?

This works by detecting the heat radiation given off by all objects & turning it into an electrical signal which is displayed on a screen. The hotter the object the brighter the image. Typically used by the police & military to spot run away miscreants.

Infrared is also ideal for remote controls of TVs and videos. It’s ideal for sending harmless signals over short distances without interfering with other radio frequencies (like the Tv channels).

Visible Light:

Effects on living tissue: activates sensitive cells in the retina

Uses: seeing, optical fiber communication

UV (Ultraviolet) Rays:

Effects on living tissue: kills living cells in high doses, lower doses can cause cells to become cancerous, causes tanning

Uses: fluorescent tubes, tanning, security, marking

X-Rays:

Effects on living tissue: kills living cells in high doses, lower doses can cause cells to become cancerous.

Uses: imaging internal structures in the body, studying the atomic structure of materials

Gamma rays:

Effects on living tissue: kills living cells in high doses, lower doses can cause cells to become cancerous, kills cancerous cells

Uses: kills bacteria in food, sterilize medical equipment, treat tumors, treats cancer without surgery

Similarities between Gamma, UV, and X-rays:

• Can kill normal cells in high doses

• in lower doses can cause cells to become cancerous