4.16 Light Energy Lesson

​4.16 Light Energy

• ​Light Travels.

  • electromagnetic wave - a wave that travels at the speed of light

  • invisible - not able to be soon.

  • laser - a tool that uses a strong beam of light.

  • visible - able to be seen

• More about light.

  • opaque - not allowing light to pass through.

  • ray - a thin beam of light

  • translucent - allowing some light to pass through, but not all

  • transparent - allowing light to pass through.

• How does light Behave?

  • absorb - to soak up

  • reflect - to send light back from a shiny surface.

  • refract - to bend a light wave.

​Light Travels

The sun and other stars are always giving off energy in the form of electromagnetic waves. (Light is an electromagnetic wave.)

• Light travels a 186,000 miles per second or 300 thousand kilometers per second.

• The speed of light is the speed limit of the universe.

• X-rays, radio waves, and microwaves are electromagnetic waves but invisible to us.

• If you see an object, light has been emitted or reflected by the object.

  • a light source emits light

    • emit - to give off

​Light Travels very fast but on the scale of the universe it may be considered slow.

• If we shoot a laser at the moon it takes three seconds to get back from the moon.

• When astronaut were on the moon.

  • People had to wait 3 seconds to get an answer to their questions.

​Lasers

​A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Multiple Choice

Arianna sees the image of a duck in the water. What causes this image?

• Light is coming from under the water

• Light is being absorbed by the rays through the water.

• Light is being refracted through by the rays bending through the water

• Light is being reflected by the rays bouncing off the surface of the water

Multiple Choice

Construction workers wear reflector to be seen at night. Reflectors need __________ energy to be seen.

• Thermal

• Heat

• Light

• Mechanical

Light reflection

What is a light wave?

• Tiny particles called photons moving very fast.

How are we able to see things?

• Light travels in a straight line to an object, bounces off, then travels back to the human eye. We can see!

Behavior of a light wave

• Travels in a straight line

• Travels very, very fast

Types of light

• Natural light: made from Earth

• Artificial light: made by man

Multiple Choice

How are we able to see?

• Light travels in a circular wave and disappears.

• Light travels in a straight line, reflects off an object, and enters the eyeball.

• Light travels through the object, circles it, then returns to the eyeball.

Properties of a light wave

• Reflection: light bounces off the object

• Refraction: bending of light - when the light moves from one medium to another (air to water)

• Transmitting: light goes through an object

• Absorbing: Light soaks into something

Multiple Select

What object below would cause light to reflect off of it?

• wall in your house

• a pillow

• a rug

• a mirror

Multiple Choice

I can see light transmit (go through) what object below?

• mirror

• window

• bed

Multiple Choice

What object may absorb (soak in) light?

• white t-shirt

• black t-shirt

• no t-shirt

How does light travel through objects?

• tranparent: all light travels through the object.

• translucent: some light travels through the object.

• opaque: no light travels through the object

Multiple Choice

Which object below is transparent?

• wooden table

• a window

• a shower curtain

• a wall

How do sunglasses help us see?

• When light hits an object, the light reflects and enters our eyeballs.

• If the light that is reflected is super bright, we may have to close our eyes or shade our eyes.

• OR.... WEAR SUNGLASSES!!!

Light Travels: Refraction

• Light transmits through an object.

• It changes direction when it passes from one material (medium) to another.

• It is the bending of light.

Seeing Color

• Different materials absorb more light of certain colors and reflect more light of other colors.

• Colors are the way we see reflected light.

Multiple Choice

When light goes from one medium (material) to another, it will bend. This is called

• absorption

• reflection

• refraction

• transmission

Multiple Choice

The colors we see are the light that gets reflected off of the object.

• True

• False

To See Color: Black

• The object absorbs most colors of light

• Light energy changes to heat energy

Multiple Choice

What color is only seen when most of the colors of light are absorbed by an object?

• black

• green

• orange

• white

To See Color: White

• The object reflects most colors of light

• Not as much chance for light energy to change to heat energy.

Multiple Choice

What color is only seen when most the colors of light are reflected off the object?

• black

• green

• orange

• white

Light does 1 of 3 things when it hits an object

• Reflects

• Refracts

• Absorbs

​Movement of Light

​Light waves move in a straight line and can travel through empty space (vacuum).

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​Light will continue to move in a straight line unless an opaque object gets in the way. Then a shadow is formed.

​

​Light can also be reflected and refracted.

​Light Reflection

​Reflection happens when light bounces off an object and moves in another direction.

​

​The light will still travel in a straight line, but just in a different direction.

​Refraction

Refraction happens when light gets bent in transparent materials such as water, air, glass, or a prism.

​Refraction can cause:

• ​Objects to look bent like in water.

• ​Objects to look bigger like through a lens.

• ​A rainbow to appear when light gets broken into its 7 colors.

Multiple Choice

Lenses, like camera lenses or microscopes...

• reflect light

• refract light

• absorb light

Multiple Choice

What do smooth, shiny surfaces do?

• reflect light

• refract light

• absorb light

Multiple Choice

When we see a rainbow, we see

• light being reflected

• light being refracted

• light being absorbed

Multiple Choice

What spiral galaxy do we live in?

• Andromeda Galaxy

• Dwarf Galaxy Saggitarius

• Milky Way Galaxy

• Snickers Galaxy

What is a Light-Year?

For most space objects, we use light-years to describe their DISTANCE. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km).

The Andromeda Galaxy

The nearest large galaxy to us, Andromeda, is 2.5 million light-years away. So, we see Andromeda as it was 2.5 million years in the past. The universe is filled with billions of galaxies, all farther away than this. Some of these galaxies are much farther away.

Multiple Choice

The distance light can travel in one year is ______________

• 15,000 kilometers

• 1 light-year

• 15 Astronomical Units

• 6,000 miles

Multiple Choice

A light-year is a measure of

• time

• speed

• distance

• brightness

Multiple Choice

What travels the FASTEST?

• Light

• Sound

• You

Multiple Choice

How long does it take light from the Sun to reach us?

• 8 minutes

• 1 light year

• 5 milllion years

• 17 days