Chp 18.1 - Electromagnetic Waves

Chp 18.1 - Electromagnetic Waves

Pg 532-538Pg 532-538

Electromagnetic waves Electromagnetic waves Waves make it possible for us to:

Heat up our food in the Microwave oven Take xrays of our bones and teeth Watch television and get our favorite music to our radio

Carry cell phone conversations See different colors

Without light waves we wouldn’t be able to see anything at all

Waves make it possible for us to: Heat up our food in the Microwave oven Take xrays of our bones and teeth Watch television and get our favorite music to our radio

Carry cell phone conversations See different colors

Without light waves we wouldn’t be able to see anything at all

Electromagnetic WavesElectromagnetic Waves Are transverse waves consisting of changing electric fields and changing magnetic fields

Carry energy from place to place like mechanical waves but differ in how they are produced and how they travel

Are transverse waves consisting of changing electric fields and changing magnetic fields

Carry energy from place to place like mechanical waves but differ in how they are produced and how they travel

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How are they produced?How are they produced? Produced by constantly changing fields

An electric field in a region of space exerts electric forces on charged particles.

Electric fields are produced by electrically charged particles changing magnetic fields.

A Magnetic field in a region of space produces magnetic forces

Magnetic fields are produced by Magnets changing electric fields vibrating charges.

Produced by constantly changing fields

An electric field in a region of space exerts electric forces on charged particles.

Electric fields are produced by electrically charged particles changing magnetic fields.

A Magnetic field in a region of space produces magnetic forces

Magnetic fields are produced by Magnets changing electric fields vibrating charges.

How are they produced?How are they produced? Electromagnetic waves are produced when an electric charge vibrates or accelerates.

Electromagnetic waves are produced when an electric charge vibrates or accelerates.

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How they travelHow they travel Because changing electric fields produce changing magnetic fields, and changing magnetic fields produce changing electric fields, the fields regenerate each other

As they regenerate, their energy travels in the form of a wave

Electromagnetic waves do not need a medium to travel through

Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter

Because changing electric fields produce changing magnetic fields, and changing magnetic fields produce changing electric fields, the fields regenerate each other

As they regenerate, their energy travels in the form of a wave

Electromagnetic waves do not need a medium to travel through

Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter

How they travelHow they travel Electromagnetic Radiation = Transfer of energy by electromagnetic waves traveling through matter or across space

Electromagnetic Radiation = Transfer of energy by electromagnetic waves traveling through matter or across space

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Michelson’s ExperimentMichelson’s Experiment In 1926 Albert Michelson measured the speed of light more accurately than ever before

Completed his experiment on the top of Mount Wilson in California

Shined a bright light and used a stationary mirror and a rotating mirror 53.4 km away. With his values he calculated the speed of light quite accurately

In 1926 Albert Michelson measured the speed of light more accurately than ever before

Completed his experiment on the top of Mount Wilson in California

Shined a bright light and used a stationary mirror and a rotating mirror 53.4 km away. With his values he calculated the speed of light quite accurately

Speed of Electromagnetic Waves

Speed of Electromagnetic Waves When a thunderstorm is approaching you can see the

sky light up before you hear the thunder rumble As the storm comes closer the time between when the flash occurs and the rumble begins becomes smaller

Light travels much faster than sound

Light and all Electromagnetic waves travel at the same speed in a vacuum

The speed of light in a vacuum or c is equal to 300,000,000 m/s. Or 3.00 x 108 m/s c = 3.00 x 108 m/s

When a thunderstorm is approaching you can see the sky light up before you hear the thunder rumble

As the storm comes closer the time between when the flash occurs and the rumble begins becomes smaller

Light travels much faster than sound

Light and all Electromagnetic waves travel at the same speed in a vacuum

The speed of light in a vacuum or c is equal to 300,000,000 m/s. Or 3.00 x 108 m/s c = 3.00 x 108 m/s

Wavelength and Frequency of Electromagnetic Waves

in a vacuum

Wavelength and Frequency of Electromagnetic Waves

in a vacuum Electromagnetic Waves vary in wavelength and frequency

The speed of an electromagnetic wave is the product of its wavelength and frequency Speed = wavelength x frequency As the wavelength increases, the frequency decreases

Electromagnetic Waves vary in wavelength and frequency

The speed of an electromagnetic wave is the product of its wavelength and frequency Speed = wavelength x frequency As the wavelength increases, the frequency decreases

EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.

Wave Model

Particle Model

EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.

Wave Model

Particle Model

Theories of Electromagnetic Radiation

In 1801, Thomas Young showed that light behaves like a wave Interference only occurs when two or more waves overlap

Double Slit Experiment - pass light through two slits and an interference pattern is observed

Constructive Interference – an overlap in waves cause an increase in amplitude

Destructive interference – an overlap in waves cause a decrease in amplitude

In 1801, Thomas Young showed that light behaves like a wave Interference only occurs when two or more waves overlap

Double Slit Experiment - pass light through two slits and an interference pattern is observed

Constructive Interference – an overlap in waves cause an increase in amplitude

Destructive interference – an overlap in waves cause a decrease in amplitude

Evidence for Wave Model

Photoelectric Effect - light striking a metal can cause electrons to be emitted from the metal

Photons – are packets of electromagnetic energy The greater the frequency of an EM wave, the more energy each of its photons have

Blue light has a higher frequency than red light so photons of blue light have more energy than photons of red light

Blue light causes emissions of electrons from metal but red light does not because blue light is higher energy

Photoelectric Effect - light striking a metal can cause electrons to be emitted from the metal

Photons – are packets of electromagnetic energy The greater the frequency of an EM wave, the more energy each of its photons have

Blue light has a higher frequency than red light so photons of blue light have more energy than photons of red light

Blue light causes emissions of electrons from metal but red light does not because blue light is higher energy

Evidence for the Particle Model

The closer you are to a source of light the brighter the light appears

Intensity is the rate at which a wave’s energy flows through a given unit of area – (brightness of light)

Intensity of light decreases as photons travel farther from the source

The closer you are to a source of light the brighter the light appears

Intensity is the rate at which a wave’s energy flows through a given unit of area – (brightness of light)

Intensity of light decreases as photons travel farther from the source

What is Intensity of light?

Ex. Flashlight’s brightness Ex. Distance a paint nozzle is to the piece

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