# Lesson 3 Light Notes

Chapter 12 Lesson 3-Light
Vocabulary
1. Wavelength-
2. Photon-
3. Translucent-
4. Image-
5. Refraction-
6. Prism-
7. Spectrum-
8. Electromagnetism-
Notes
What is light?
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Light is made of vibrating electric and magnetic energy.
o
This energy travels as a wave.
o
It has both frequency and amplitude.
Light waves vibrate in the direction perpendicular to the direction of their motion.
o
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Transverse Waves
Light does not depend on compressions or rarefactions.
o
Can travel with or without a medium.
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In a vacuum, light travels very fast (300,000 km/s or 186,000 miles/s).
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Travels slowly through mediums like air, water, or glass.
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Scientists think that nothing travels faster than light.
o
Speed of light may be the speed limit of our universe.
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When you multiply the wavelength of a wave by its frequency, you get the speed of that wave.
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Light is also a particle.
o
Light travels in straight lines called light rays.
o
Does not have mass, but does have momentum.
o
Particles of light are called photons.
o
Energy of a single photon is very small.
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Photon of red light is 0.0000000000000000003 Joules of energy.
o
Each photon acts like a wave with frequency.
o
Higher frequency has more energy.
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Scattering-when light strikes an object’s surface causing photons to bounce off at random
angles.
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Absorbed objects gain energy.
o
Transformed into heat.
o
Darker objects absorb more light than lighter objects.
Light may pass through objects.
o
These objects are transparent.
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Objects that blur light as it passes through are translucent.
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Objects that allow little to no light through are opaque.
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Whether an object is opaque, translucent, or transparent depends on its material, thickness,
and color of light.
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Opaque and translucent objects block light.
o
Area behind these objects is darker (they have a shadow).


Shadows are just the absence of light.
When an object is between a light source and another object, it will cast a shadow on the other
object.

Light from the sun travels toward you at a small angle.
o
Takes a long distance for the light to hit the ground behind you.
o
As the sun rises, the angle of the sunlight increases and your shadow become shorter.
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Shadows depend on the angle and distance between a light source and an object, and between
the object and the place where the shadow is cast.
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The closer a light source is to an object, the larger the shadow an object will cast.
How does light bounce and bend?
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Light reflects off a mirror like sound echoes off a cliff.
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Reflection is just the organized scattering of a wave.
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Law of reflection
o
The angle of an incoming light ray equals the angle of the reflected light ray.
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An image in a flat mirror appears to be behind the mirror.
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Mirrors that curve in are concave.
o
Form many kinds of images.
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Mirrors that curve out are convex.
o
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Ex: upright, upside down, enlarged, reduced.
Always produce images that are upright and reduced.
When you place an object in a glass of water, it appears to bend.
o
It is the light from the object that is bending.
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When light changes mediums it also changes speed.
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When light changes speed, they refract.
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Refraction is not very noticeable with sound waves.
o
With light waves you see it easily.

Rays entering a denser medium bend to make a steeper angle with the surface.
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Rays leaving a denser medium bend in the opposite direction.
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Lenses use refraction to shape images.

o
Used in eyeglasses to make objects appear in focus.
o
Used in cameras and telescopes.
The size and location of the image depend on where the object and lenses are in relation to
each other.
Why do we see colors?
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Our eyes see light waves with different wavelengths as different colors.
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Visible light waves with longer wavelengths look red.
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Visible light waves with shorter wavelengths look violet.
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All the colors in between have wavelengths in the middle of those two.
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White light is actually just a collection of many different wavelengths mixed together.
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Different wavelengths of light will reflect and refract at different angles.
o
This is why when white light is refracted by raindrops it is spread out into a rainbow.
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You can separate light using a prism.
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Whether an object scatters, absorbs, or transmits light may depend on the wavelength of the
light.
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When light hits an opaque object it is scattered and/or absorbed.
o
Objects appear the color of light that they scatter.
o
Absorb all other colors of light.
Translucent object
o
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Some colors are absorbed and others pass through.
Translucent objects
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Appear the color of the light that passes through them.
o
Absorb all other colors of light.
The picture on a color television is made up of red, green, and blue dots of light.
o
We can create any color of light by mixing red, green, and blue light in the right
amounts.
o
Red, Green, and Blue are called primary colors of light.
o
If mixed equally, they will produce white light.
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Magenta, cyan, and yellow are often used to create color by scattering.
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Magenta scatters only red and blue.
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Cyan scatters only blue and green.
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When the two are mixed, magenta absorbs cyan’s green, and cyan absorbs magenta’s red.
o
Together they only scatter blue. (The color they share)
Is all light visible?
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Light is made of electric and magnetic waves that can move through space.
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Light is just a form of electromagnetic radiation.
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Different forms of electromagnetic radiation all travel at the speed of light and can move
through a vacuum.
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They differ in wavelength and energy.
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Together they make up the electromagnetic spectrum.
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The sun can produce all forms of electromagnetic radiation.
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Most of the radiation from the sun is infrared, visible and ultraviolet light.
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Solar flares give off all forms of electromagnetic radiation when they erupt.