Grade 8 - Unit 3: Light And Optical Systems ~ Topics 1-3

Front 1

What is light?

Back 1

A form of energy that you can see.

Front 2

What is a natural source of light?

Back 2

A natural source radiates light in all directions, and is not man-made. It is something that occurs naturally in nature. For example: Sun, stars, or fire.

Front 3

What is an artificial source of light?

Back 3

An artificial light source radiates light in all directions, and is man-made. For example: Light bulbs.

Front 4

What are photons?

Back 4

Photons are small bundles of energy that all light is made up of. Photons can be transformed into other types of energy.

Front 5

What is intensity?

Back 5

Intensity means how bright the light source is. If it is very bright, it has a high intensity, and if it is dim, it has a low intensity. The higher intensity something is, the more photons it has, meaning more energy can be transformed.

Front 6

What is an incandescent source?

Back 6

An incandescent source is the source of light that emits light when it is heated to a high temperature. The energy path for an incandescent source is Electrical Energy→Thermal Energy→Visible Light Energy

Front 7

What is a fluorescent source?

Back 7

The energy path for a fluorescent source is Electrical Energy→Energy Absorbed by Mercury Particles→Ultraviolet Light Energy→Energy Absorbed by Particles→Visible Light Energy, meaning that an electric current causes the mercury to vapor inside the tube and give off ultraviolet energy, and the phosphor coating on the inside of the tube absorbs the ultraviolet energy, and the coating glows, producing light immediately.

Front 8

Why is a fluorescent source hard to dispose of?

Back 8

A fluorescent source is hard to dispose of because of the toxic mercury inside.

Front 9

What is a phosphorescent source?

Back 9

A phosphorescent source is light energy stored by certain particles and released later as visible light later. For example: The star stickers on ceilings.

Front 10

What is a chemiluminescent source?

Back 10

A chemiluminescent source is light that can be released by chemical reactions. For example: Snap glow sticks. The energy path for a chemiluminescent source is Chemical Energy→Visible Light Energy.

Front 11

What is a bioluminescent source?

Back 11

A bioluminescent source is light emitted from chemical reactions inside living things. For example: Deep sea fish or fireflies.

Front 12

What are all objects that emit light called?

Back 12

All objects that emit light are called luminous.

Front 13

What is a ray?

Back 13

A ray is a straight imaginary line that represents the path of a beam of light. They are used in ray models or diagrams.

Front 14

How is a shadow made?

Back 14

A shadow is made in the absence of light from a certain light source, because light cannot bend around a opaque object.

Front 15

What is a transparent object?

Back 15

A transparent object is a completely clear or see-through object that light can pass through without being affected. For example: Glass, air, or the lenses of your eyes.

Front 16

What is a translucent object?

Back 16

A translucent object is an object through which light rays are deflected. This means you can still see the light, but not the objects behind it. For example: A piece of paper held up to a light bulb.

Front 17

What is an opaque object?

Back 17

An opaque object is an object through which light cannot pass. It will cast shadows behind it. The light rays are totally blocked. For example: Thick textbooks, humans, etc.

Front 18

How do you calculate the cost of lighting?

Back 18

Step 1: Convert watts (W) to kilowatts (kW).

(W/1000)=x

Step 2: Multiply kilowatts (kW) by hours (hrs).

(x times # of hrs)=kW•hrs

Step 3: Number of kilowatt hours (kW•hrs) x cents per hour = Money amount per hour of lighting.

Front 19

What is reflection?

Back 19

Reflection is the process in which light strikes a surface and bounces back off that surface.

Front 20

What is the incident ray?

Back 20

The ray that comes from a light source and strikes the surface.

Front 21

What is the reflected ray?

Back 21

The ray that bounces off the surface.

Front 22

Label the ray diagram.

Back 22

Front 23

What is the law of reflection?

Back 23

The angle of reflection equals the angle of incidence.

Front 24

What is the law of light?

Back 24

Light travels in straight lines.

Front 25

How does a smooth surface affect reflections?

Back 25

Smooth surface reflect light very uniformly.

Front 26

How does a rough surface affect reflections?

Back 26

Rough surfaces reflect light in a scattered manner because the normal lines point in different directions. This causes the reflected rays to be scattered and cannot form an image.

Front 27

What is a convex mirror?

Back 27

It is a mirror that curves outward, or has a bulge. It is useful for seeing more objects in a space. Cars use them, as well as stores to keep an eye out for shoplifters.

Front 28

What is a concave mirror?

Back 28

It is a mirror that curves inward, or caves in like a shiny bowl. It projects the image upside down.

Front 29

What is refraction?

Back 29

Refraction is the bending of light when it travels from one medium to another. Light bends because it changes speed when going through materials with different densities. The bending of light makes objects appear to be in a different position from where it really is.

Front 30

What is the difference between light entering a more dense medium versus leaving it?

Back 30

When light goes from one medium to one that is more dense, it will bend TOWARD the line of normal. For example: Light entering water.

When light exits a denser medium, light bends AWAY from the line of normal. For example: Light exiting water.

Front 31

How do the angle of incidence and the angle of refraction relate?

Back 31

When the angle of incidence increases, as does the angle of refraction.