ELECTROMAGNETIC

WAVES

Nature of Waves• A disturbance that transfers energy

from one place to another is called a wave.

• The source of any wave is a vibration.

• A substance or region through which a wave is transmitted is called a medium.–Mechanical waves, such as sound

waves, require a medium to travel.

Transverse Waves• An electromagnetic wave consists of vibrating

electric and magnetic fields.

• An electromagnetic wave is a transverse wave that transfers electrical and magnetic energy.• Transverse waves do NOT require a medium to travel

• Unlike sound waves, electromagnetic waves can travel in a vacuum, which means they can travel through space.

• Speed of electromagnetic waves –

– 300,000,000 meters/second

– Takes light 8 minutes to travel from the sun to earth {150 million miles} at this speed.

In order to create the vibrating electric and magnetic fields that are characteristic of an electromagnetic wave, electrons

must move.

• Electrons are arranged in energy levels.– electrons with the lowest energy are

found closest to the nucleus– electrons with higher energy are found

farther away from the nucleus

• If an electron moves closer to the nucleus, energy is released & an electric and magnetic field is created.

• These fields form electromagnetic waves.

How are electromagnetic waves created?

Types of Electromagnetic Waves• Radio waves• Microwaves (a type of radio wave)• Infrared light• Visible light – red, orange, yellow,

green, blue, & violet• Ultraviolet light (UV)• X-rays• Gamma rays

Electromagnetic Spectrum

Electromagnetic Spectrum

• Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.

• Used in radios & TVs– A radio picks up radio waves through an

antenna and converts it to sound waves.– Each radio station in an area broadcasts at a

different frequency. # on radio dial tells frequency.

• MRI (MAGNETIC RESONACE IMAGING)– Uses short wave radio waves with a magnet to

create an image

Electromagnetic Spectrum

Radio Waves

MRI Images

• Microwaves – have the shortest wavelengths and the highest frequency of the radio waves.– Used in microwave ovens –• Microwaves are absorbed by water, fats and

sugars. When they are absorbed they are converted directly into atomic motion = heat.• Metal reflects microwaves, which is why

metal pans do not work well in a microwave oven.

Electromagnetic Spectrum

Microwaves

• Other uses –– Used by cell phones and pagers.– RADAR (Radio Detection and Ranging)• Used to find the speed of an object by

sending out radio waves and measuring the time it takes them to return

Electromagnetic Spectrum

Microwaves

• Infrared = below red– Shorter wavelength and higher

frequency than microwaves.– You can feel the longest ones as

warmth on your skin–Warm objects give off more heat

energy than cool objects.

Electromagnetic Spectrum

Infrared Rays

• Thermogram –a picture that shows regions of different temperatures in the body.– Temperatures are calculated by the

amount of infrared radiation given off.– Therefore people give off infrared rays.

• Other uses –– cooking - special lamps that emit

thermal infrared waves are often used in fast food restaurants

– T.V. remote controls

Electromagnetic Spectrum

Infrared Rays

Electromagnetic Spectrum

Infrared Rays

• Visible spectrum – these are e/m waves we can see

• When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors –– Red, Orange, Yellow, Green, Blue, & Violet– Longest wavelength = red light– Shortest wavelength = violet (purple) light

Electromagnetic Spectrum

Visible Light

LIGHT: What is it?• Atoms -–electrons release light when falling

down to lower energy levels–photons - packets of energy

released when the electrons fall• Light = a stream of photons, or

packets of energy, released when electrons move from higher energy levels to lower energy levels

• Shorter wavelength and higher frequency than visible light

• Carry more energy than visible light• Use in hospitals to kill bacteria cells –

sterilization of equipment• Causes your skin to produce vitamin D –

good for teeth & bones (helps with the absorption of calcium)– Too much can cause skin cancer • Use sun block to protect against (UV rays)

Electromagnetic SpectrumUltraviolet Light

• Shorter wavelength and higher frequency than UV-rays

• Carry a great amount of energy• Can penetrate most matter• Bones and teeth absorb x-rays. (The light

part of an x-ray image indicates a place where the x-ray was absorbed)

• Too much exposure can cause cancer – lead vest at dentist protects organs from unnecessary

exposure

• Used by engineers to check for tiny cracks in structures– The rays pass through the cracks and the cracks appear dark

on film.

Electromagnetic Spectrum

X-Rays

• Gamma rays have the smallest wavelengths and the most energy of any other wave in the e/m spectrum.– They are generated by radioactive atoms and

in nuclear explosions.– They are also produced by such violent events

as supernova explosions (the way massive stars die).

• Gamma-rays are used to kill cancerous cells

• Gamma-rays travel to us from outer space & are absorbed by the Earth's atmosphere.

Electromagnetic Spectrum

Gamma Rays

• All electromagnetic waves travel at the same speed – 300,000,000 m/s in a vacuum

• They all have different wavelengths and different frequencies.– Longer wavelength lowest frequency– Shorter wavelength highest frequency– The higher the frequency the higher the

energy.

SUMMARY