Holt Science & Technology O3: Nature of Light

1. WARMUP
 What do you think light is?
 Is light made of matter? Can light travel through space?

2. THE NATURE OF LIGHT
APPLIED PHYSICS: BOOK O, CHAPTER 3

3. SECTION 1: WHAT IS LIGHT?
By the end of this section, you should be able to:
 Describe light as an electromagnetic wave.
 Calculate distances traveled by light by using the speed of light.
 Explain why light from the sun is important.

4. LIGHT: AN ELECTROMAGNETIC WAVE
 Light is a type of energy that travels as a wave. But unlike most
other types of waves, light does not require matter through
which to travel.
 Light is an electromagnetic wave (EM wave).

5. LIGHT: AN ELECTROMAGNETIC WAVE
 An electromagnetic wave is a wave that consists of electric and
magnetic fields that vibrate at right angles to each other.

6. LIGHT: AN ELECTROMAGNETIC WAVE
 An electric field surrounds every charged object. You see the
effect of electric fields whenever you see objects stuck together
by static electricity.
 A magnetic field surrounds every magnet. Because of magnetic
fields, paper clips and iron filings are pulled toward magnets.

7. LIGHT: AN ELECTROMAGNETIC WAVE
 An EM wave can be produced by the vibration of an electrically
charged particle.
 This vibration makes electric and magnetic fields vibrate also.
Together, the vibrating fields are an EM wave that carries energy.
 The transfer of energy as electromagnetic waves is called
radiation.

8. LIGHT FROM THE SUN
 Scientists have yet to discover anything that travels faster than
light.
 In the near vacuum of space, the speed of light is about 300,000
km/s. Light travels slightly slower in air, glass, and other types of
matter.

9. HOW FAST IS LIGHT?

10. LIGHT FROM THE SUN
 EM waves from the sun are the major source of energy on Earth. For
example, plants use photosynthesis to store energy from the sun.
 Animals use and store energy by eating plants or by eating other
animals that eat plants.
 Even fossil fuels store energy from the sun. Fossil fuels are formed
from the remains of plants and animals that lived millions of years
ago.

11. LIGHT FROM THE SUN
 Only a very small part of the total energy given off by the sun
reaches Earth. The sun gives off energy as EM waves in all
directions. Most of this energy travels away in space.

12. SECTION 1 REVIEW
p.65 #2-9

13. WARMUP
 Describe the weather conditions necessary to see a rainbow.
 Why do rainbows form?

14. SECTION 2: THE ELECTROMAGNETIC SPECTRUM
By the end of this section, you should be able to:
 Identify how electromagnetic waves differ from each other.
 Describe some uses for radio waves and microwaves.
 List examples of how infrared waves and visible light are
important in your life.
 Explain how ultraviolet light, x-rays, and gamma rays can be
both helpful and harmful.

15. CHARACTERISTICS OF EM WAVES
 The light that you can see is called visible light. However, there
is light that you can’t see.
 The light that you can see and light that you cannot are both
kinds of electromagnetic (EM) waves.
 Other kinds of EM waves include x-rays, radio waves, and
microwaves.

16. CHARACTERISTICS OF EM WAVES
 All EM waves travel at 300,000 km/s in a vacuum.
 The entire range of EM waves is called the electromagnetic
spectrum. The electromagnetic spectrum is divided into regions
according to the length of the waves.

18. RADIO WAVES
 Radio waves cover a wide range of waves in the EM spectrum.
Radio waves have some of the longest wavelengths and the
lowest frequencies of all EM waves.
 Radio waves are any EM waves that have wavelengths longer
than 30 cm. Radio waves are used for broadcasting radio
signals.

19. RADIO WAVES
 Radio stations can encode sound information into radio waves
by varying either the waves’ amplitude or frequency.
 Changing amplitude or frequency of a wave is called
modulation. AM stands for amplitude modulation, and FM
stands for frequency modulation.

20. RADIO WAVES

21. RADIO WAVES
 AM radio waves have longer wavelengths than FM radio waves.
AM radio waves can bounce off the atmosphere and thus can
travel farther than FM radio waves.
 But FM radio waves are less affected by electrical noise than AM
radio waves, so music broadcast from FM sounds better than
music from AM stations.

22. RADIO WAVES
 TV signals are also carried by radio waves. Most TV stations
broadcast radio waves that have shorter wavelengths and higher
frequencies than those from radio stations.
 Some waves carrying TV signals are transmitted to artificial
satellites orbiting Earth. The waves are amplified and sent to
ground antennas. They the signals travel through cables to TVs
in homes.

23. MICROWAVES
 Microwaves have shorter wavelengths and higher frequencies
than radio waves. Microwaves have wavelengths between 1 mm
and 30 cm.
 Microwaves are used to send information over long distances.

24. MICROWAVES

25. MICROWAVES
 Cellular phones send and receive signals using microwaves.
Signals sent between Earth and artificial satellites in space are
also carried by microwaves.
 Microwaves are used in radar. Radar (radio detection and
ranging) is used to detect the speed and location of objects.

26. MICROWAVES
 Radar sends out microwaves that reflect off an object and return
to the transmitter. The reflected waves are used to calculate
speed.

27. INFRARED WAVES
 Infrared waves have shorter wavelengths and higher frequencies
than microwaves. The wavelengths of infrared waves vary
between 700 nanometers (nm) and 1 mm.
 Almost everything give off infrared waves, including the sun,
buildings, trees, and your body. The amount of infrared waves
an object emits depends on the object’s temperature. Warmer
objects give off more infrared waves than cooler objects.

28. INFRARED WAVES

29. VISIBLE LIGHT
 Visible light is the very narrow range of wavelengths and
frequencies in the EM spectrum that humans’ eyes respond to.
Visible light waves have wavelengths between 400 nm and 700
nm.
 The visible light from the sun is white light. White light is visible
light of all wavelengths combined.

30. VISIBLE LIGHT
 Humans see different wavelengths of visible light as different
colors. The longest wave-lengths are seen as red light. The
shortest wave-lengths are seen as violet light.
 The range of colors is called the visible spectrum.

31. ULTRAVIOLET LIGHT
 Ultraviolet light (UV light) is another type of EM wave produced
by the sun. Ultraviolet waves have shorter wavelengths and
higher frequencies than visible light.
 The wavelengths of UV light wave vary between 60 nm and 400
nm.

32. ULTRAVIOLET LIGHT
 Too much UV light can cause sunburn. UV light can also cause
skin cancer and wrinkles, and damage the eyes.
 Ultraviolet waves produced by UV lamps are used to kill bacteria
on food and surgical tools. Small amounts of UV light are
beneficial to your body, causing skin cells to produce vitamin D.

33. X-RAYS & GAMMA RAYS
 X-rays have wavelengths between 0.001 nm and 60 nm. X-rays
can pass through many materials, making them useful in the
medical field.
 However, too much exposure to x-rays can damage or kill living
cells.

34. X-RAYS & GAMMA RAYS

35. X-RAYS & GAMMA RAYS
 Gamma rays have wavelengths shorter than 0.1 nm. They can
penetrate most materials easily.
 Gamma rays are used to treat some forms of cancer. Doctors
focus the rays on tumors inside the body to kill the cancer cells.
 Gamma rays are also used to kill harmful bacteria in foods, such
as meat and fresh fruits.

36. SECTION 2 REVIEW
p.73 #2-12