1. Section 25.1 – Properties of Light pp. 604-611
Chapter 25 - Light
Section 25.1 – Properties of Light pp

2. TERMS TO LEARN
Electromagnetic (EM) wave– a wave that can travel through space and matter. It consists of changing electric and magnetic fields.
Radiation – the emission of energy in the form of EM waves

3. LIGHT Light is an EM wave. Light can travel through space and matter.
A field is a region around an object that can exert a force on another object without actually touching it (ex.: a magnet is surrounded by a magnetic field that can pull a paper clip toward it).

4. AN ELECTROMAGNETIC WAVE

5. 25.1 Properties of light
Light travels fast over long distances and carries energy and information.
Light travels in straight lines, but can be bent by lenses or reflected by mirrors heat and warmth.
Light has color and can be bright or dim.

6. 25.1 The electromagnetic spectrum
Light, like sound and heat, is a form of energy.
The visible light we see is part of the electromagnetic spectrum.

7. 25.1 Properties of light
You see book pages because light in the room reflects from the page to your eyes.
Your eyes and brain use the information carried by the light to make a mental picture.

8. 25.1 Light is produced by atoms
Most light is produced by atoms.
When you put some energy into the atom, it excites the atom’s electrons.
Light is produced when the electron releases this energy.

9. 25.1 Incandescent light
Making light with heat is called incandescence.
Atoms in the filament convert electrical energy to heat and then to light.
Incandescent bulbs are inefficient, but their waste heat can be useful.

10. 25.1 Fluorescent light
To make light, fluorescent bulbs use high-voltage electricity to energize atoms of gas in the bulb.
These atoms release the electrical energy directly as light (not heat), in a process called fluorescence.

11. 25.1 Color and energy
When all the colors of the rainbow are combined, we see light without any color.
We call the combination of all colors white light.

12. 25.1 Color and energy
Compare the hot, blue flame from a gas stove to the orange flame of a match.
The light from a gas flame is blue (high energy) and the light from a match is red-orange (low energy).

14. 25.1 The speed of light
The speed at which light travels through air is about 300 million meters per second.
The speed of light is so important in physics that it is given its own symbol, a lower case “c”.

15. 25.1 Speed of light
The speed at which electromagnetic waves travel through air is about 300 million meters per second.
The speed of light is so fast that when lightning strikes a few miles away, we hear the thunder after we see the lightning.

16. 25.1 Wavelength and Frequency of Light
Because the wavelength of light is so small, scientists measure it in nanometers.
One nanometer (nm) is one billionth of a meter ( m).

17. 25.1 Wavelength and Frequency of Light

18. 25.1 What kind of wave is light?
A sound wave is a oscillation of air.
A water wave is an oscillation of the surface of water.
An oscillation of electricity or magnetism creates electromagnetic waves.

19. 25.1 Electromagnetic waves
If you could shake the magnet up and down 450 trillion times per second, you would make waves of red light with a frequency of about 450 THz.

20. 25.1 Electromagnetic spectrum
The entire range of electromagnetic waves, including all possible frequencies, is called the electromagnetic spectrum.
This spectrum includes visible light and invisible waves:
radio wave
microwaves
infrared light
ultraviolet light
X-rays
gamma rays

22. RADIO WAVES
Have some of the longest wavelengths and lowest frequencies of all the EM waves
Are low energy waves

23. AM VS. FM WAVES Amplitude Modulation (A.M.)
Frequency modulation (F.M.)
Can travel farther than FM
More information can be encoded than AM
Can reflect off the ionosphere
Passes through the ionosphere
Have longer wavelengths than FM
Have shorter wavelengths than AM

24. TV AND RADIO WAVES
TV uses radio waves that have shorter wavelength and higher frequency than those used by radio stations.
Most TV stations are broadcast using A.M. and F.M.
F.M. waves carry sound; A.M. waves carry pictures

25. MICROWAVES
Have shorter wavelength and higher frequency than radio waves.
Carry more energy than radio waves.
Microwaves are also used in radar (radio detection and ranging).

26. INFRARED WAVES
Have shorter wavelengths and higher frequency than microwaves.
Can carry more energy than microwaves and radio waves

27. INFRARED WAVES The Sun is a source of IR waves.
Stars, planets, buildings, humans and trees also emit IR waves.

28. IR WAVES
The amount of IR radiation emitted by an object depends on the temperature of the object. Warmer objects give off more IR radiation than cooler ones.
Your eyes cannot see IR radiation but there are devices that can detect it (i.e. night vision goggles)

29. VISIBLE LIGHT

30. UV LIGHT Also produced by the Sun.
Has shorter wavelength and higher frequency than visible light.
Carries more energy than visible light.

31. EFFECTS OF UV WAVES Positive Effects Negative Effects
Used to kill bacteria in food
Overexposure can cause sunburn, skin cancer, eye damage
Causes skin cells to produce Vitamin D
Overexposure can cause wrinkles and premature aging of the skin

32. X-RAYS
Have the shortest wavelengths and highest frequency of all EM waves.
X-rays carry a lot of energy and can penetrate many materials.
Too much exposure to x—rays can damage or kill living cells

33. GAMMA RAYS
Carry large amounts of energy and can penetrate materials very easily.
Every day you are exposed to small amounts of gamma rays that do not harm you.
Radiologists focus these on tumors to kill cancer cells.
A negative effect of gamma radiation is that they kill healthy cells.