1. 16.1 Properties and Sources of Light

2. Chapter 16 Objectives Describe at least five properties of light.
Describe the meaning of the term “intensity.”
Use the speed of light to calculate the time or distance traveled by light.
Explain how we perceive color in terms of the three primary colors.
Explain the difference between the additive and subtractive color processes.
Arrange the colors of light in order of increasing energy, starting with red.
Describe light in terms of photons, energy, and color. 2

3. Chapter 16 Vocabulary Terms
additive process
black
blue
CMYK color process
color
cone cell
cyan
fluorescence
green
incandescence
infrared
intensity
inverse square law
light ray
magenta
photoluminescence
photon
photoreceptor
pixel
red
RGB color model
rod cell
speed of light
spherical pattern
subtractive process
ultraviolet
white light
yellow

4. Inv 16.1 Properties and Sources of Light
Investigation Key Question:
What are some useful properties of light? 4

5. 16.1 Properties and Sources of Light
Light travels almost unimaginably fast and far.
Light carries energy and information.
Light travels in straight lines.
Light bounces and bends when it comes in contact with objects.
Light has color.
Light has different intensities, it can be bright or dim.

6. 16.1 Electric Light
The process of making light with heat is called incandescence.
Incandescent bulbs generate light when electricity passes through a thin piece of metal wire called a filament.
The filament heats up and gives off light.

7. 16.1 Electric Light
The other common kind of electric light is the fluorescent bulb.
Fluorescent bulbs convert electricity directly to light without generating a lot of heat.
Fluorescent bulbs use high-voltage electricity to energize atoms of gas that fill the bulb.

8. 16.1 Light carries energy and power
Light is a form of energy that travels.
The intensity of light is the amount of energy per second falling on a surface.
Most light sources distribute their light equally in all directions, making a spherical pattern.
Because light spreads out in a sphere, the intensity decreases the farther you get from the source.

9. 16.1 Light intensity
The intensity of light from a small source follows an inverse square law because its intensity diminishes as the square of the distance.

10. 16.1 Light carries information
The fiber-optic networks you read about are pipelines for information carried by light.

11. 16.1 Light carries information
In some cities, a fiber-optic cable comes directly into homes and apartments carrying telephone, television, and Internet signals.

12. 16.1 The speed of light
The speed at which light travels through air is approximately 300 million meters per second.
Light travels almost a million times faster than sound.

13. 16.1 The speed of light
The speed of light is so important in physics that it is given its own symbol, a lower case c.
The best accepted experimental measurement for the speed of light in air is 299,792,500 m/sec.
For most purposes, we do not need to be this accurate and may use a value for c of 3 × 108 m/sec.

14. Calculating time for light and sound
Calculate the time it takes light and sound to travel the distance of 1 mile, which is 1,609 meters.
You are asked for time.
You are given distance.
Use v = d ÷ t , rearrange to solve for t = d ÷ v
Solve for sound: t = (1,609 m) ÷ (340 m/s) = 4.73 s
Solve for light: t= (1,609 m) ÷ (3 x 108 m/s) = 5.4 x 10-6 s

15. 16.1 Reflection and refraction
When light moves through a material it travels in straight lines.
When light rays travel from one material to another, the rays may reflect.
The light that appears to bounce off the surface of an object is shown by a reflected ray.

16. 16.1 Reflection and refraction
Objects that are in front of a mirror appear as if they are behind the mirror.
This is because light rays are reflected by the mirror.
Your brain perceives the light as if it always traveled in a straight line.

17. 16.1 Reflection and refraction
Another example of refraction of light is the twinkling of a star in the night sky
As starlight travels from space into the Earth’s atmosphere, the rays are refracted.
Since the atmosphere is constantly changing, the amount of refraction also changes.

18. 16.1 Reflection and refraction
The light that bends as it crosses a surface into a material refracts and is shown as a refracted ray.