Light

Facts

Light is energy – electromagnetic energy (energy that is electric and magnetic)

Travels in a straight path unless…it goes through a new material (medium) then it may bend or slow down

Travels in wavesTravels VERY fast!The speed of light:

186,000 mi/sec

How fast is 186,000 miles/second?

WavelengthsWe measure the length of a light wave by

measuring between two crests (high points) or troughs (low points).

If the waves are close together, it has a short wave length.

Far apart = long wave length

When light hits a surface, it bounces or REFLECTS off of the surface.

If light hits a smooth surface, it will bounce at a predictable angle.

If light hits a rough surface, it bounces off at all kinds of angles.

Look at how the surface affects these water reflections.

Concave mirrorscurve inward-like a “cave”

Close up – image is enlarged, right-side upFurther away – image is enlarged, but upside-

downThe further away you move, the smaller the

image gets

Convex Mirrors

curve outwardThe image is always

smaller and right-side up.

Used for side view mirrors on cars, to prevent shoplifting, and in our stairwells here at school.

Which is convex? Which is concave?

How light passes through objects

Opaquecompletely blocks light from coming

throughTranslucent

Lets only part of the light throughView is blurry

TransparentAllows light to pass through with almost no

disturbanceCan be clear or coloredClear view

Refraction

When light rays bend as they are passing from one substance to another

Happens when light rays pass through at an angle

Lenses – curved transparent materials that refract (bend) light to make images

Convex lensesCurve outLight rays bend together after passing through“e” in convex = together

Convex lens – the rays angle together

•If the lens is close to your eye, the image you see will be right-side up and enlarged.

•If the lens is further away, the image will be upside down.

Concave LensesCurves inward (like a cave)Light rays pass through and move apart“a” in concave = apart

Concave Lens

The image you see is always smaller and right-side up.

What would happen if you put both of them together?

Hmm…..

Visible Light WavesWhite light is actually all the colors of light combinedEach color of light has a different wave lengthRed has the longest; violet the shortest.

When the light ray passes through a prism, the rays bend at different angles because their wave lengths are different

Since red’s wavelengths are longer, they bend the least when passing through the prism

Violet’s are shortest, so they bend the most.

Visible Light Spectrum

A rainbow acts as a prism and a mirror. The sun shines through the drops of water (prism) and the backside of the raindrop is like a mirror, reflecting the bent colors back to us.

BrainPop Rainbow

ROY G BIV

Helps us remember the colors of the visible light spectrum.

R = redO = orangeY = yellowG = green B = blue I = indigoV = violetReview with BrainPop!!!

How does color work?

When light hits an object, it either reflects (bounces off) or is absorbed.

An object’s color depends on which light waves are absorbed or reflected.

If an object is yellow, it’s because all the colors except yellow are absorbed by the object. The yellow light is reflected back and what we see yellow!!

If none of the light colors are absorbed, then all of them reflect, and the object looks white.

If all are absorbed, no light is reflected, and the object looks black.

Electromagnetic Spectrum

Remember that visible light is electromagnetic energy that travels in waves

Our eyes are only sensitive to the wavelengths of light from violet to red.

Our eyes don’t pick up wavelengths shorter or longer than these

Electromagnetic Spectrum

BrainPop - Electromagnetic Spectrum