Science Focus Topic 1 Notes: What is Light
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Simply stated, light is the form of energy you can see. This energy can be produced naturally by the sun or fire, or artificially by light-producing technologies, like batteries.
Radiation is the wave like transfer of light from its source in all directions. Light is often called radiant energy. Light from the sun is formed by nuclear fusion (Off the Wall p. 176)
The First Basic Principle of Light
'Light is a form of energy' When light reaches a surface, it can be absorbed and transformed into other types of energy.
The amount of energy a surface receives depends on the intensity of the light.
? into electrical energy
? into thermal energy
? into chemical energy
Solar cells change light into electricity
Cameras change light into thermal images
Trees convert light energy into food (chemical energy)
The more intense the light, the more light can be absorbed.
Sources of Light
Other sources of Light Energy can come from the Earth's minerals including:
Natural Light Sources
Artificial Light Sources
(heat causing a filament of metal to glow - visible light)
Electrical energy ---? Thermal energy ---? Visible light energy
Candles or Oil Lamps
(ultraviolet light is absorbed by fabric particles, which in turn emit some of the energy as light - glowing)
Ultraviolet light ---? Energy absorbed ---? Visible light
energy by particles energy
(light energy is stored and released later as visible light)paint
Bioluminescence(light produced by living organisms)
(light energy released by chemical reactions)glow sticks
Chemiluminescence Movies (Shackwave/Flash)
Chemical energy ---? Visible light energy
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UV Light Technologies Light and Color
THERMOLUMINESCENCE and TRIBOLUMINESCENCE
The Cost of Lighting
Electrical energy costs money to produce. A watt is a unit of electrical power.
The cost is calculated by how much of the electrical energy is used over a certain period of time. Calculations are made in kW.h's. 1 kW.h is 1000 watts of electrical energy operating for 1 hour.
Example: Calculate the cost of leaving a 60W light bulb on for 10 hours.
Convert 60W to kW by dividing by 1000
60 W / 1000 = 0.06 kW
Calculate the number of kW hours
0.06 kW x 10 hours = 0.6 kW.h
Calculate the cost by multiplying the number of hours by the cost per kW.h
If the cost per kW.h is $0.08
The cost of electricity to operate the 60W light bulb for 2 hours would be
0.6 kW.h x $0.08 = $0.048
(4.8 cents - or about 5 cents)
The Ray Model of Light
'Light travels in straight lines'
Because of this principle, the ray model of light can help to explain certain properties light. A ray is a straight line that represents the path of a beam of light. The ray model helps to explain how shadows can be formed, when the ray of light is blocked by an object.
Light travels in straight lines until it strikes a surface.
The type of surface will determine how the light will continue.
If the surface is transparent, the light will continue in a straight path through the object
If the surface is translucent, the light will be diverted (refracted) after it passes through
If the surface is opaque, the light will be blocked and not allowed through the object
Diagram (Figure 3.12 p.185)