Waves and Electromagnetic Radiation

1
Waves and Electromagnetic Radiation

• The Sciences chapter 6

2
Maxwell, in 1867, proposed that light is an
electromagnetic wave.

• The spectrum of visible light, from red to
  violet, is only an octave or so in the range of
  invisible radiations. There is a whole keyboard
  of information all the way from the longest
  wavelengths of radiowaves (the low notes) to the
  shortest wavelengths of X-rays and beyond (the
  highest notes) (Bronowski, p. 353).

3
Figure 6-11 The electromagnetic spectrum
includes all kinds of waves that travel at the
speed of light, including radio, microwave,
infrared, visible light, ultraviolet, X-rays, and
gamma rays. Note that sound waves, water waves,
seismic waves, and other kinds of waves that
require matter in order to move travel much
slower than light speed.
4
Waves transfer energy without transferring mass.
5
Energy Transfer by Waves
Figure 6-1 You can use a domino to knock over
other dominoes in two different ways (a) you can
throw a domino, or (b) you can trigger a wave of
dominoes.
6
A wave

• Is a traveling disturbance
• It carries energy from place to place without
  requiring matter to travel across the intervening
  distance.

7
Properties of Waves

• Wavelengths
• Frequency
• Velocity
• Amplitude

8
Figure 6-2 A cross section of a wave reveals the
characteristics of wavelength, velocity, and
amplitude. Successive wave crests are numbered 1,
2, 3, and 4. An observer at the position of the
clock records the number of crests that pass by
in a second. This is the frequency, which is
measured in cycles per second, or hertz.
9
Relationship among wavelength, frequency, and
velocity

• The velocity of a wave is equal to the length of
  each wave times the number of waves that pass by
  each second.
• Wave velocity (m/s) wavelength (m) x frequency
  (Hz)
• Sample Problem One tube of a wind chime produces
  sound at a frequency of 440 Hz. Assuming the
  speed of sound is 340 m/s, what is the wavelength
  of sound produced by this chime?
• Wavelength velocity / frequency
• 340 meters per second / 440 Hertz 0.77 m
• Also see Example 6-1, p. 119.

10
Two kinds of waves
Figure 6-4 Transverse (a) and longitudinal (b)
waves differ in the motion of the wave relative
to the motion of individual particles.
11
Speed of Light Speed of Sound

• 300,000,000 m/s
• 186,000 miles/s

• 340 m/s
• 760 miles/hr

12
Example problem 6-2The human ear can hear
sounds at frequencies from 20 to 20,000 Hz. Organ
pipes producing these notes would be about half
the wavelength.

• Lowest note wavelength
• Velocity / frequency
• 340 m/s / 20 Hz
• 17 m
• Organ pipe 8.5 m

• Highest note wavelength
• Velocity / frequency
• 340 m/s / 20,000 Hz
• 0.017 m
• Organ pipe 0.009 m

13
How Sound is Produced

• Sound is a form of energy caused by vibrating
  matter.

14
How Sounds Travel

• Vibrations push against molecules in the air and
  press them closer together
• Molecules pushed compression
• Molecules spread rarefaction

15
Sound Travel in Different States

• The speed of sound in air is about 336 meters/sec
  or 1100 ft/sec
• In liquids, the molecules are closer together and
  carry the vibrations more easily and quickly (4X
  gt).
• In solids, the atoms are very close together and
  carry the vibrations very easily and quickly
  (9-15X gt).

16
Characteristics of Sound

• Intensity the loudness or softness of a
  sound

• Pitch how high or low the sound seems

17
Characteristics of Sound

• Pitch - how high or low sound seems
• Intensity - loudness or softness
• Quality - the mix of frequencies that allow us to
  distinguish between different sounds
• Interference waves from two different sources
  come together (constructive or destructive)

18
Echoes

• An echo is a sound wave that bounces back
• must be at least 17 meters (or 56 ft) away from
  the reflecting surface (closer and reflected
  sound wave blends with original)

19
The Human Voice

• 2 strong bands of tissue called vocal cords
• --The tighter the vocal cords, faster
• they vibrate, the higher the pitch.
• --Increase volume by
• increasing force of air
• blown between the
• vocal cords.

20
Speed of Light Speed of Sound

• 300,000,000 m/s
• 186,000 miles/s

• 331 m/s
• 760 miles/hr

21
Doppler Effect

• If a listener or the source of a sound is moving,
  the listener may hear a pitch that is different
  from the frequency of the source.
• The change in pitch heard when the source of
  sound is moving relative to the listener is the
  Doppler effect.

22
Figure 6-9 The Doppler effect occurs whenever a
source of waves is moving relative to the
observer of the waves. (a) Sound waves spread out
from a source in all directions stationary
listeners hear the same pitch. (b) Sound waves
from a moving source seem to increase or decrease
in pitch, depending on whether the sound is
approaching or receding. (c) The Doppler shift
for light waves cause a blueshift for approaching
sources, and a redshift for receding sources.
23
(No Transcript)
24
Electromagnetic waves
25
Electromagnetic spectrum
26
Figure 6-11 The electromagnetic spectrum
includes all kinds of waves that travel at the
speed of light, including radio, microwave,
infrared, visible light, ultraviolet, X-rays, and
gamma rays. Note that sound waves, water waves,
seismic waves, and other kinds of waves that
require matter in order to move travel much
slower than light speed.
27
Anatomy of the Electromagnetic Wave

• Electrical and magnetic fields arranged at right
  angles to each other
• Perpendicular to the direction the wave is moving

28
The nature of light

• Ø Light is a form of radiant energy given out by
  the Sun and other light producing bodies in the
  form of waves.
• Ø Light is the one part of a group of the em
  spectrum that we can see.
• --Consists of transverse waves, --move up and
  down as they travel forward

29
Same Speed across the whole em spectrum!

• Velocity of em waves depends on electrical and
  magnetic interactions, not on the properties of
  the wave itself.

• All em waves move at the speed of light!
• Wavelength x frequency 300,000 km/sor 186,000
  mi/s

30
The energy of em wavesOscillating comb
andglowing embers p.125-6
31
Light travels in straight lines

• Light travels at a speed of 186,000 miles/sec
  (300,000 km/sec)
• (in 8 minutes, light to travels Sun to Earth)
• Thus we see things happen at the exact moment
  they are happening.

32
With regard to light, materials are

• Transparent
• Translucent
• Opaque

33
Law of Refection

• Ø      angle of incidence is equal to the angle
  of reflection (holds true for all smooth,
  polished surfaces)

34
The Plane Mirror

• light striking the mirror passes thru the
  transparent glass, and then almost all the light
  is reflected back by the shiny, opaque silver

35
Mirror Convex
Concave
36
Refraction of Light lenses

• convex lens
• light rays passing thru a convex lens are bent
  toward the thicker middle

• concave lens
• light rays passing thru a concave lens are bent
  toward the thicker ends

37
Spectrum of visible light
38
(No Transcript)
39
Mixing Colors of Light
40
Electromagnetic Spectrum

• Radio Waves
• Microwaves
• Infrared Radiation
• Visible Light

• Ultraviolet Radiation
• X-rays
• Gamma Rays

41
Study Guide, end of chapter 6

• Discussion Questions 1, 2, 3, 4, 6, 8, 9.
• Problems 1, 5, 6, 7.
• Chemistry Reading, push on to read chapters 8
  10.