What is light? Light is a form of energy that can be detected by - - PowerPoint PPT Presentation

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Light Energy and Its Sources 308-8 identify and describe properties of visible light What is light? Light is a form of energy that can be detected by the human eye. Light cannot be touched or tasted, but it can warm things up so it gives

SLIDE 1

Light Energy and Its Sources

308-8 identify and describe properties of visible light

SLIDE 2

What is light?

Light is a form of energy that can be detected by the human eye. Light cannot be touched or tasted, but it can warm things up so it gives heat energy to

bjects.

SLIDE 3

Energy

Energy is the ability to do work. Energy can be neither created nor destroyed. Energy can only be transformed from one form to another.

SLIDE 4

Where does light energy come from?

Light energy comes form two different sources, natural and artificial.

SLIDE 5

What is the most important source for natural light?

The sun is the most important source for natural light.

SLIDE 6

Objects that emit (give off) their own

light are called luminous.

Objects that do not emit light, but

reflect it from other sources are called nonluminous.

SLIDE 7

What are some examples

f luminous objects?

SLIDE 8

Luminous objects are objects that give off their own light.

SLIDE 9

What are some examples

f nonluminous objects?

SLIDE 10

Nonluminous objects are objects that do not give off light.

SLIDE 11

Why is the Moon nonluminous?

The Moon is nonluminous because it reflects light from the Sun

SLIDE 12

What are some common forms of luminous energy?

Chemical energy Electrical energy Nuclear energy Thermal energy

SLIDE 13

Sources of Light

1. Light from Incandescence –

Incandescent source means the process of giving off light because of the high temperature. Light produced by a flame, candle, campfire, or light bulb.

SLIDE 14

SLIDE 15

2. Light from Phosphorescence –

Some materials, called phosphors, give off light for a short time after you shine a light on them. They store the energy and then release it as light energy.

SLIDE 16

3. Light from Electric Discharge – An

electric discharge is the process by which a gas releases light because of electricity passing through it.

SLIDE 17

4. Light from Fluorescence –

The release of light from a substance caused by exposure to radiation from an external source.

SLIDE 18

Where are fluorescent lights used?

Schools Offices Homes

SLIDE 19

What happens inside a fluorescent light?

In fluorescent lighting, the tube glows when ultraviolet light energy strikes the phosphors lining the tube. Phosphorescent light sources continue to emit light for much longer period after receiving light energy. The tube stops emitting light immediately after the electric current is turned off.

SLIDE 20

What is a chemical reaction?

When two chemicals react and a new compound is formed. When substances are mixed and new substances are formed, a chemical reaction has occurred. Change that takes place when two or more substances (reactants) interact to form new substances (products).

SLIDE 21

5. Light from Chemiluminescence –

Chemiluminescene is the process of changing chemical energy into light energy with little or no change in temperature.

SLIDE 22

6. Light from Bioluminescence –

some living things, such as fish, can make themselves luminous using a chemical reaction like chemiluminescence.

SLIDE 23

Give examples of bioluminescence.

Firefly Glow worm Zebra Fish Hawaiian bobtail squid

SLIDE 24

Bacteria Fungi (mushrooms)

SLIDE 25

Daytime Nighttime

SLIDE 26

Properties of Light

Light travels in a straight line (rectilinear

propagation)

Light travels at a speed of 300 000 km/s

in air

Reflection
Refraction and dispersion
Light travels in a vacuum and in some
ther types of media

* We will explore these properties in more detail throughout this unit.

SLIDE 27

Understanding Concepts

SLIDE 28

Questions
Page 271
1, 2, 3, 4

SLIDE 29

Which of the following are luminous?

A. Campfire
B. The Moon
C. A hot toaster filament

SLIDE 30

The campfire and hot toaster are luminous.

WHY?

For, luminous objects are objects that give off their own light.

SLIDE 31

Describe how a flashlight can be luminous.

A flashlight becomes luminous when it is switched

n, allowing the chemical energy in the battery to

become electrical energy, which in turn becomes light energy (heat) in the bulb.

SLIDE 32

Describe how it can also be nonluminous.

The flashlight can be nonluminous when it is turned off.

SLIDE 33

Investigation

On your own, you are going to investigate

“fuzzy” and “sharp” shadows.

What are they? Show some examples

(draw or print pictures 2 pictures for each)

What causes one to be sharp and the
ther to be fuzzy?
I am just looking for a little write-up about

each to be passed in for evaluation.

SLIDE 34

Light Box

You are going to make a light box to

see how light travels in a straight line.

See instruction sheet.