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MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 10: SOUND AND LIGHT WAVES
CLASS NOTES
WAVE DEFINITIONS
1. The amplitude, A, is the maximum distance an object moves away from its equilibrium.
2. The period, T, is the time it takes an object to execute one complete cycle of motion.
3. The frequency, f, is the number of cycles or vibrations per unit of time.
4. The wavelength, , is the distance between crests or troughs.
WAVE DIAGRAM
PERIOD AND FREQUENCY
The period (T) of a wave is the time required to complete a full cycle of its motion. Frequency (f) is
the reciprocal of period:
f = 1 cycle / T
FREQUENCY
Frequency is measured in hertz, the number of cycles completed per second:
1 Hz = 1 cycle / sec
Example 1. A hummingbird’s wings move back and forth in 0.002 seconds. What is the frequency of
their waves?
1A.
(1) f = 1 cycle / T
(2) f = 1 cycle / 0.002 s
(3) f = 500 cycles / s
(4) f = 500 Hz
WAVE SPEED EQUATION
Since waves occur at regular intervals, they are a type of simple harmonic motion. One common wave
equation is:
v=f
[velocity = frequency x wavelength]
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INTEGRATED SCIENCE
MR. SURRETTE
VAN NUYS HIGH SCHOOL
Example 2. If a train of freight cars, each 10 m long, rolls by you at the rate of three cars a second,
what is the speed of the train?
2A.
(1) v = f 
(2) v = (3 Hz) (10 m)
(3) v = (3 cycles / sec) (10 m)
(4) v = 30 m/s
Example 3. If a water wave vibrates up and down three times each second and the distance between
wave crests is 2 meters, what is the wave speed?
3A.
(1) v = f 
(2) v = (3 Hz) (2 m)
(3) v = (3 cycles / sec) (2 m)
(4) v = 6 m/s
Example 4. A 60-Hz source produces air waves that spread out at 340 m/s. What is the wavelength of
these waves?
4A.
(1) v = f 
(2)  = v / f
(3)  = 340 m/s / 60 Hz
(4)  = 340 m/s / 60 cycles / s
(5)  = 5.68 m
TRANSVERSE WAVES
A transverse wave is a pulse or wave in which the motion of the medium is perpendicular to the motion
of the wave.
TRANSVERSE WAVES
COMPRESSIONAL WAVES
A compressional wave is a longitudinal pulse or wave caused by the compression of a fluid, like a
sound wave in air.
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INTEGRATED SCIENCE
MR. SURRETTE
VAN NUYS HIGH SCHOOL
COMPRESSIONAL WAVE
SOUND
Sound is a compressional wave that travels through an elastic medium. The speed of sound depends on
air temperature. It is about 340 m/s.
SOUND WAVES
PITCH
Pitch is a quality of sound that depends on the frequency of the sound waves: the higher the frequency,
the higher the pitch.
THE DOPPLER EFFECT
The apparent change in frequency heard by an observer because of relative motion is called the Doppler
effect.
THE DOPPLER EFFECT
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
DOPPLER EFFECT EQUATION
The general equation for the Doppler effect is:
f’ = f [(V +/- Vo) / (V +/- Vs)]
f’ = the frequency heard
f = frequency of the source
V = speed of sound (usually 340 m/s)
Vo = relative speed of observer
Vs = relative speed of source
THE ELECTROMAGNETIC SPECTRUM
Visible light is part of the electromagnetic spectrum (EMS). Other parts of the spectrum include
ultraviolet, infrared, x-rays, gamma rays, microwaves, and radio waves.
SPEED OF LIGHT
All light waves travel at the speed of light:
c = 3.0 x 108 m/s
ELECTROMAGNETIC WAVE
ELECTROMAGNETIC SPECTRUM
REFLECTION AND REFRACTION
A line drawn perpendicular to a surface where an incident ray strikes is called the normal line. Angles
of reflection and refraction are measured relative to the normal.
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INTEGRATED SCIENCE
MR. SURRETTE
VAN NUYS HIGH SCHOOL
REFLECTION AND REFRACTION
REFLECTION/REFRACTION RULES
1. When an incident ray undergoes partial reflection and partial refraction, the incident, reflected and
refracted rays are all in the same plane.
2. The path of a light ray through a refracting surface is reversible.
3. As light travels from one medium into another, the frequency does not change.
THE LAW OF REFLECTION
The law of reflection states that the angle of incidence equals the angle of reflection:
1 = 1’
INDEX OF REFRACTION
Each transparent medium is characterized by the index of refraction n which equals the ratio of the
speed of light in the medium to the speed of light in a vacuum:
n=c/v
(c = 3.0 x 108 m/s)
Example 5. If the velocity of light through an unknown liquid is measured at 2.40 x 108 m/s, what is the
index of refraction?
(c = 3.0 x 108 m/s)
5A.
(1) n = c / v
(2) n = 3.0 x 108 m/s / 2.40 x 108 m/s
(3) n = 1.25
Example 6. A beam of light in air is incident on the surface of a rectangular block of clear plastic (n =
1.49). If the velocity of the beam before it enters the plastic is 3.0 x 108 m/s, what is its velocity after
emerging from the block?
6A.
3.0 x 108 m/s
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INTEGRATED SCIENCE
MR. SURRETTE
VAN NUYS HIGH SCHOOL
DIRECTION OF REFRACTION
Light rays bend towards the normal line as they pass into a denser medium and away from the normal
line as they pass into a lighter medium.
SNELL’S LAW
Snell’s law predicts the path of refracted light rays. This is one practical form of Snell’s law:
n = sin1 / sin2
Example 7. A ray of light in air is incident on an air-to-glass boundary at an angle of 30.0o with the
normal. If the index of refraction of the glass is 1.65, what is the angle of the refracted ray within the
glass with respect to the normal?
7A.
(1) n = sin1 / sin
(2) sin2 = sin1 / n
(3) sin2 = sin 30o / 1.65
(4) sin2 = 0.5 / 1.65
(5) sin2 = 0.303
(6) 2 = sin-1
2 = 17.64o
DISPERSION AND PRISMS
As light travels from one medium into another, its frequency remains constant but the wavelength
changes:
n = o / n
Note: One result of dispersion is the rainbow of colors that emerges when white light strikes a prism.
Example 8. Light with a wavelength 0f 700 nm becomes 545 nm as it enters a sheet of glass. What is
the index of refraction for this glass? (one nm = 1 x 10-9 m)
8A.
(1) n = o / n
(2) n = 700 nm / 545 nm
(3) n = 1.28
TOTAL INTERNAL REFLECTION
Total internal reflection occurs when light rays traveling in a denser medium (n1) are incident on a
medium of lesser index of refraction (n2). Total internal reflection occurs at angles of incidence  > c.
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INTEGRATED SCIENCE
MR. SURRETTE
VAN NUYS HIGH SCHOOL
TOTAL INTERNAL REFLECTION
sinc = n2 / n1
Example 9. If the critical angle for internal reflection inside a certain transparent material is 48.0o, what
is the index of refraction of the material? (Air is outside the material).
9A.
(1) sinc = n2 / n1
(2) n1 = n2 / sinc
(3) n1 = 1.00 / sin 48o
(4) n1 = 1.35
LENSES
A very practical case of refraction occurs in lenses. Lens (a) below converges light and is called a
converging lens. Lens (b) diverges light, and is called a diverging lens.
CONVERGING AND DIVERGING LENSES
FEATURES OF LENSES
Some key features of lenses are shown below. The principle axis is the line joining the centers of
curvatures of the two surfaces of the lens. The focal point is the point at which a beam of light parallel
to the principal axis converges. The focal length of the lens is the distance between the center of the
lens and either focal point.
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
KEY FEATURES OF CONVERGING LENS
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