Topic 1: What is light?

Essential Learning Outcome

What is Light?

Light is a form of energy that you can see.

We have two types of light sources:1. Natural Light Sources2. Artificial Light Sources

The Sun is a Star

All stars in the universe are sources of light.

Light spreads out or radiates, from the sun and other stars in all directions.

This type of energy transfer does not require matter; it is known as radiation.

Energy such as light that travels by radiation is often called radiant energy.

Less than one tenth of a millionth of a percent of the sun’s energy actually reaches the earth.

Nonetheless plants, people and other animals are totally dependent on this energy.

Where does energy come from?

The first basic principle of light is that “light is a form of energy”.

Light can be converted from one form of energy to another form of energy;

Thermal energyElectrical energy Chemical energy

Light intensity

The brightness or intensity of light is the amount of energy a surface will receive.

The greater the brightness or intensity, the more energy the surface receives per unit time.

Sources of Light

Light sources can be natural or artificial.

There are 5 Light sources;1. Incandescent Sources2. Fluorescent Sources3. Phosphorescent Sources4. Chemiluminescent Sources5. Bioluminescent Sources

Fill in the table in your notes by reading pages 179-183 in your textbook.

The Cost of Lighting

Electrical energy costs about eight cents per kilowatt hour.

A Watt (W) is a unit of electrical power.

A kilowatt hour (kWh) is one thousand watts of electrical power operating for one hour.

Formula for Cost

Cost = Amount of energy x Unit price

($) (kWh) (c/kWh)

Calculate the cost of running a 60 W light bulb for 10 hours• Convert 60W to kW (divide by 1000)

= 0.06 kW• Calculate how many kWh by

multiplying the energy by the time run

= 0.06 kW x 10 hours = 0.6 kWh• Calculate how much money by

multiplying by the unit price of electricity (8 cents per kWh)

= 0.6 x 8 = 4.8 cents

The Ray Model of LightSome properties of light

are best described by considering light as a wave. Other properties of light are best described by considering light as a particle.

The ray model of light uses a straight line, or ray, to show the direction the light wave is traveling.

Different materials can either transmit, absorb, or reflect light.

Transparent materials allows light to pass through freely.

Translucent materials lets most light through but scatters the light leaving.

Opaque materials prevent light from passing through.

How are Shadows created?

A shadow is created when an opaque object absorbs light rays.

Shadows demonstrate that light travels in straight lines.

A ray diagram shows how the distance from the light source affects the size of the shadow an object makes.

Vocabulary• Light• Natural light source • Radiates • Radiation • Radiant energy• Artificial light source• Ray model • Ray diagram • Transparent • Translucent • Opaque

• Incandescent • Fluorescence• Phosphorescence • Chemiluminescen

ce• Bioluminescence • Non-luminous

Homework

One page 187 in your textbook, do questions 1-7.

• Be neat• Use complete sentences