# Light Waves Unlike sound, light does NOT need a medium to propagate or move through. Light travels the fastest through vacuum space – whereas sound does.

## Presentation on theme: "Light Waves Unlike sound, light does NOT need a medium to propagate or move through. Light travels the fastest through vacuum space – whereas sound does."— Presentation transcript:

Light Waves Unlike sound, light does NOT need a medium to propagate or move through. Light travels the fastest through vacuum space – whereas sound does not exist in a vacuum! The speed of light in vacuum space is 300,000,000 m/s (3.0 x 108 m/s). Unlike sound, light is a transverse propagation of energy.

Light is an electromagnetic wave
Light is an electromagnetic wave. It has an electric part and a magnetic part.

The Electromagnetic Spectrum or EM spectrum
contains all of the frequencies or wavelengths of visible and invisible light .

Frequency vs. Wavelength
Waves with the longest wavelengths (λ) have the lowest frequencies and the lowest energy. Ex: Radio, Microwave, Infrared Waves with the shortest wavelengths (λ) have the highest frequencies and the highest energy. Ex: Ultraviolet, X-Ray, Gamma

Selective Transmission
Some substances allow only some frequencies of light to pass through; also called partial transparency. Ex: Blue glass allows blue light frequencies to pass through but absorbs all other frequencies and turns them into heat. The glass warms up a little. Ex: The earth’s atmosphere allows us to send radio waves to operate spacecraft.

Reflection of Light Law of reflection:
Light waves bouncing off a surface or at the boundary of a medium. Law of reflection: Angle of incidence = angle of reflection

Selective Reflection Things reflect the colors they do NOT absorb.
The reflected color (frequency) is visible to the human eye. Ex: The leaves of plants have a chemical called chlorophyll that absorbs all colors (light energy), except the green frequencies they reflect.

Visible Light = R O Y G B V ed range e l l ow reen i o l et l ue
Only reflected colors are visible to the human eye.

Chlorophyll Light Absorption
Chlorophyll b Chlorophyll a V B G Y O R

Refraction of Light Light refracts (bends) when it goes from one medium into another, like from air to water. This pencil appears broken in water because of the refraction of light.

When white light passes through a narrow slit and then through a prism, each wavelength (λ) refracts (or bends) at a different angle. Violet (the shortest wave) bends the most and red (the longest wave) bends the least, hence the rainbow.

Illusions caused by refraction
During sunsets, the sun appears higher in the sky than it actually is because of refraction.

The amount of bending depends on the material’s index of refraction.
Diamonds have a high index of refraction (lots of bending), while glass has a lower index of refraction (less bending).

Wavelengths (λ) of visible light
Human eyes send a different signal to the brain for each λ. The brain interprets each as a different color.

Polarization of Light Light is polarized when all its planes of travel are reduced to one single plane. We can use this property of light to make sunglasses or other polarized materials.

Doppler Effect: The shift in frequency when the light source and the observer are moving toward or away from each other. Ex: Galaxies that are moving away from ours appear red (redshift) , while those moving toward ours appear blue (blueshift).

Doppler Effect:

Light Diffraction A light beam going through a very narrow opening spreads out as the opening gets smaller. The light blurs and loses its brightness. Light diffraction is a problem to scientists who study things with a light microscope.

Lenses A convex lens focuses parallel light rays onto a focal point.
A concave lens spreads parallel light rays away from each other.

Compare: Light and sound can be refracted.
Light and sound can be reflected. Light and sound can be diffracted. Light and sound have a Doppler effect. Light and sound are both waves of energy.

Contrast: Light can be polarized; sound cannot.
Light speed is almost a million times faster than sound. Light is a transverse wave; sound is longitudinal. Light can go through a vacuum; sound cannot. Light is electromagnetic; sound is compressional.

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