Section 1 – Electromagnetic Waves

What are electromagnetic waves? What do microwaves, cell phones, police radar,

television, and X-rays have in common?

All of them use electromagnetic waves

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

Electromagnetic Spectrum

What are electromagnetic waves? Electromagnetic waves differ from mechanical waves

in how they are produced and how they travel

How are they produced?

Electromagnetic waves are produced by constantly changing fields (electric field and magnetic field)

Changing electric fields produce changing magnetic fields and changing magnetic fields produce changing electric fields

The fields regenerate each other!

What are electromagnetic waves? Electromagnetic waves can travel through a vacuum,

or empty space, as well as through matter

Speed of Electromagnetic Waves Thunderstorm – You see the lightening before you

hear the thunder

Therefore electromagnetic waves travel faster than sound waves

In fact, electromagnetic waves travel at 300,000,000 m/s (3.00 x 108 m/s)

Electromagnetic waves always travel this speed (in a vacuum)

Speed of Electromagnetic Waves The wavelength of light from a laser is 630

nm (630 x 10-9 m). What is the frequency of the light?

Frequency = Speed/Wavelength

*Have to convert the wavelength into meters!!!

Frequency = 3.0 x 108 m/s = 4.8x1014 Hz

630 x 10-9 m

Wavelength and Frequency Because the speed of ALL electromagnetic waves is

3.00 x 108 meters the wavelength is inversely proportional to the frequency.

This means that if frequency increases, then wavelength decreases…and visa versa.

Wave vs. Particle?? Light has properties of both waves and particles

The particles of light are called photons

The photons of higher frequency light carry more energy

Blue light has a higher frequency than red light, and therefore more energy than red light

1800’s, Herschel – Measured temperature of different colors of light

Intensity Intensity of light decreases as photons travel farther

from the source

Think of how a street light closer to you looks brighter than one further away…they both are emitting the same amount of energy, but the one further away is less intense.

Section 2 – The Electromagnetic Spectrum

The Electromagnetic Spectrum The full range of frequencies of electromagnetic

radiation is called the electromagnetic spectrum

Visible light is only a SMALL portion of the spectrum

The electromagnetic spectrum includes radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays

Uses of the Electromagnetic Spectrum Radio Waves

Longest wavelength (lowest frequency)

Used in radio and television technology

Music and voices are changed into electronic signals coded onto radio waves

AM (amplitude modulation)

FM (frequency modulation)

Uses of the Electromagnetic Spectrum Microwaves

Are actually the shortest-wavelength radio waves

When water or fat molecules in the food absorb microwaves, the thermal energy of these molecules increases

Microwaves only penetrate a few cm into the food

Microwaves are also what make your cell phones work!

Process is much the same as how radios work

Uses of the Electromagnetic Spectrum Radar

Radio detection and ranging

Sends out short bursts of radio waves, measures the time it takes for them to return (much like sonar)

Uses the Doppler effect to calculate speed

Uses of the Electromagnetic Spectrum Infrared Red

Infrared rays are used as a source of heat and to discover areas of heat differences

You can’t see infrared, but you feel it has heat

Warmer objects give off more infrared radiation than cooler objects

Detect troubles in power lines, find Earthquake victims

Uses of the Electromagnetic Spectrum Visible Light

Each wavelength in the visible spectrum corresponds to a specific frequency and has a particular color

Birds can see ultraviolet light!

Uses of the Electromagnetic Spectrum Ultraviolet Rays (UV)

Exposure to ultraviolet rays helps your skin produce vitamin D (which helps your body absorb calcium)

Excessive exposure can cause sunburn, wrinkles, and skin cancer (melanoma)

Uses of the Electromagnetic Spectrum X-Rays

Teeth and bone (more dense) absorb X-rays, while the X-rays pass through the softer tissues leaving an image on a film

Dangerous in large amounts

Airports use X-rays to “see” inside of luggage

Uses of the Electromagnetic Spectrum Gamma Rays

Safe in VERY tiny amounts, otherwise deadly

Used in radiation therapy to kill cancer cells (chemotherapy)

Pipelines are checked for rust or cracks with machines that emit gamma rays