Electromagnetic Waves

• Electromagnetic waves are transverse waves consisting of changing electric and magnetic fields.

• Energy travels in the form of waves.• They can travel in a vacuum as well as

through matter. • Electromagnetic radiation- the transfer of energy by electromagnetic waves traveling through matter or across space.

Light, like sound and heat, is a form of energy.

The visible light we see is part of the electromagnetic spectrum.

Things to know…

• frequency– how often a wave passes a point in a certain time interval

• wavelength- the distance from one crest to the next or one trough to the next

The speed of light depends on the medium.

• The speed of light in a vacuum is: 3 X 108 meters per second (300,000,000 m/sec)

Electromagnetic Spectrum- the full range of frequencies of electromagnetic radiation.

This spectrum includes visible light and invisible waves:• radio wave• microwaves• infrared light• ultraviolet light• X-rays• gamma rays

The Electromagnetic Spectrum

Wavelength and Frequency

Wavelength and Frequency of Light

Because the wavelength of light is so small, scientists measure it in nanometers.

One nanometer (nm) is one billionth of a meter (0.000000001 m).

The electromagnetic spectrum includes:

Radio Waves• Has the longest wavelength and the

lowest frequency.• Uses: Radio, TV, radar, microwaves

– Radar: radio detection and ranging, a system that uses reflected radio waves to determine the velocity and location of objects

Microwaves• Microwaves are used in cooking and

communication.– Microwaves have wavelengths in the

range of centimeters.

Infrared Rays• Wavelength smaller than radio.• slightly longer than red visible light.• felt as warmth• Used as a source of heat/or to detect heat

differences.• Thermograms- color-coded pictures that show variations in temperature.

Visible Light• Each wavelength in the visible

spectrum corresponds with a specific frequency and a specific color.

• Light enables people to see, keeps people safe and helps them to communicate.

Ultraviolet Rays• Shorter wavelength and higher

frequency than violet light.• Sunlight contains ultraviolet light.

– The invisible light that lies just beyond violet light falls into the ultraviolet (UV) portion of the spectrum.

X-Rays• Have very short wavelengths.• Less than 10–8 m.

• Used in medicine, industry and

transportation by making pictures of the inside of

solid objects.

Gamma Rays• Shortest wavelength in the

electromagnetic spectrum.• wavelengths shorter than 10–10 m.

• Have the highest frequency.• Have the most energy.• Over exposure can be

deadly.• Used in the medical field

to kill cancer cells and make pictures of the brain, and in industrial situations as an inspection tool.