What is Light? Light is a form of energy that you can see. We have two types of light sources: 1. Natural Light Sources 2. 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 energy Electrical 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 Sources 2.Fluorescent Sources 3.Phosphorescent Sources 4.Chemiluminescent Sources 5.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 ($) (kWh) (c/kWh) ($) (kWh) (c/kWh)
Calculate the cost of running a 60 W light bulb for 10 hours Convert 60W to kW (divide by 1000) Convert 60W to kW (divide by 1000) = 0.06 kW Calculate how many kWh by multiplying the energy by the time run 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) 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 Light Some 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 Light Natural light source Natural light source Radiates Radiates Radiation Radiation Radiant energy Radiant energy Artificial light source Artificial light source Ray model Ray model Ray diagram Ray diagram Transparent Transparent Translucent Translucent Opaque Opaque Incandescent Incandescent Fluorescence Fluorescence Phosphorescence Phosphorescence Chemiluminescence Chemiluminescence Bioluminescence Bioluminescence Non-luminous Non-luminous
Homework One page 187 in your textbook, do questions 1-7. Be neat Be neat Use complete sentences Use complete sentences
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