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Unit IV - Wave Phenomena

I. Introduction to Waves

Wave a vibratory disturbance that travels through a material or space

Ex) sound, water waves, light, microwaves, heat rays

A.Waves and Energy

1. Waves transferenergy from one place to another with no transfer of mass

2. Waves can be produced in two ways:

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a. Vibration of particles

(requires a medium for transfer)

(mechanical wave)

b. Small changes in the strength of an electromagnetic field

(requires no medium for transfer)

ex) light, microwaves, x-rays

B.Pulses & Periodic Waves

1. Pulse single vibratory disturbance that moves from point to point

Medium only moves up and down

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Ex)

In which direction will segment X move as the wave passes through it?

(1) down, only (2) up, only

(3) down, then up, then down

(4) up, then down, then up

(4) up, then down, then up

a. When the pulse (wave) reaches a boundary with another medium, part is reflected and partis transmitted (goes through)

b. When a pulse reaches a fixed, unyielding boundary, then the pulse is completely reflectedand inverted (180)

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2. Periodic Wave series of evenly timed disturbances in a medium

C. Vibrations and Waves

1.Longitudinal medium moves parallel to the direction in which the wave travels

ex) sound - Guitar String

2.Transverse vibrational disturbance which is perpendicular to the direction in which the

wave travels

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Unlike longitudinal waves,transverse waves can be oriented in many different planes.

Ex) water waves, seismic waves, electromagnetic waves (light, microwaves, radio waves)

Ex) Longitudinal, Transverse?

Transverse

(Vibration perpendicular to wave travel)

II.Characteristics of Periodic Waves

A.Frequency(f) = #vibrations/sec

= # Cycles/sec

= Hertz (Hz)

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Frequency

- Determined by

Source of Wave,

Not Medium

Cycle = (single vibration)

Ex)

How many cycles between the dots?

3 Cycles

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Ex) 10 cycles pass a fixed point in a wave train in 5 seconds.What is the frequency of the wave?

f = 10 cycles = 2 cycles5 seconds 1 sec

f = 2 Hertz (Hz)

Ex) A wave generator operating for4 seconds produces the waves drawn below.

Top view of a periodic wave

(Each line is a crest)

How many waves are drawn between A and B? (Be careful!!)

What is the frequency of this periodic wave train?

8 cycles

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f = 8 cycles/4 sec

f = 2 cycles/sec

Sound, frequency is pitch.

Light, frequency is color.

Human Ear:

Frequency Range

20 Hz - 20,000 Hz.

dogs are capable of hearing higher pitch sounds than humans

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The range of frequencies youcan hear changes with age.

B.Period(T) time for an entire wave cycle to pass a given point in a medium

- determined by source of vibration not medium

T

(sec)

(Period)

=

1

f

Ex) The frequency of a light wave is 5.0 x 1014

hertz.

What is the period of the wave?

T = 1/f

= 1/(5.0 x 1014

hertz)

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a) 2.0 x 10-15

s

Which has the largest period?

C.Amplitude maximum change in position of a particle from its rest position during a single

vibration

determined by source of vibration, not medium

Ex) Compare waves A & B

Same Frequency

Different Amplitude

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1. Amplitude of a wave shows the amount ofenergy in the wave

a. Amplitude is a measure ofloudness forsound and brightness forcolor

A. Phase

"In Phase" (0) points on a single periodic wave that have the same displacement (from

equilibrium position) and moving in the same direction

Whole number of wavelengths apart?

A & ____ A & ____ B & ___ B & ___

A & E, A & I, A & M

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B & F, B & J, B & N

"Out of Phase" (1800)

- same displacement from equilibrium position but going in a different direction

, 1, 2 etc wavelengths apart

A & C, B & D, F & H

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B. Wavelength distance between two consecutive points in phase

y determined by medium

y symbol = lambda

- length of one cycle #m/cycle

Ex) Wavelength?

June 2000

= 5.0 m/2.5 cycles

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= 2.0 m

Ex)

Amplitude? Wavelength?

Amplitude = .10 m

Wavelength = .60 m

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Ex)

Amplitude A?, B?, C?

Jan 2004

C. Speed the number of meters a single cycle travels per second

1. V = f solve for f:

f = v/

inverse relationship

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C. Speed the number of meters a single cycle travels per second

1. V = f solve for f:

f = v/

inverse relationship

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2.Speed of wave depends on the medium

(slower in dense media)

3. Velocity sound = 3.3 x 102

m/s

(Air, Reference Table, room temperature)

Velocity light in a vacuum

= 3 x 108

m/s

About how many times faster is light

than sound?

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Reference Table

About 1 million times

Gap between time you see lightning and time you hear thunder tells ....

... distance of lightning

If time gap is small?

Lightning is close

Large gap of time?

Lightning far away

D. Doppler Effect variation in the observed frequency of a wave when there is relative motionbetween the source of the wave and the receiver

Doppler Effect V = 14 m/s

Doppler Effect V = 18

Stationary Ambulance

E. Wave Front locus of adjacent points on a wave which are in phase

Top View

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Ex) Distance between arrows= .90 cm

Wavelength of wave?

= .30 m

III. Periodic Wave Phenomena

Interference effect produced by two waves passing simultaneously through a region

1. Superposition when waves overlap, the resultant displacement is the algebraic sum of the

individual displacements of each wave

a) Constructive Interference

1)

2)

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Amplitude?

2A

3)

Waves reemerge as separate waves

b) Destructive Interference

1.

At moment of overlap, amplitudes cancel (for a moment)

Waves reemerge as separate waves

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2. Symmetrical Lines of Interference

- wave patterns produced by the overlap of 2 wave fronts in phase

Maximum Destructive Interference -

Phase Difference - 1/2 wavelength

B) Standing Wave waves produced when two waves of the same frequency and amplitude

travel in opposite direction

C) Resonance Building up of energy by adding small amounts of energy in time with thenatural frequency of an objectections in the same medium (Musical instruments)

Resonance Frequency natural frequency that an object vibrates when disturbed

D) Diffraction the spreading out of a wave into the region behind an obstacle

Amount of Diffraction

Depends on

Wavelength &

Size of Slit

IV. Light (electromagnetic waves)

A. Speed

1. 3 x 108 m/s = c (in vacuum)

(fastest speed in universe)

In air v 3 x 108 m/s

1. Law ofReflection

a. of incidence = of reflection

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... reflection always makes a V

Half the sizeof the person

The image from a plane mirror:

a. Virtual (realistic) & Upright (Straight up and down)b. Incident ray, normal line, and reflected rays are all in the same planec. The distance the object is in front of the mirror equals the distance the image is

behind the mirroryyy 2. Two Basic Kinds ofReflection

yyy a.Regular Reflection reflection off a polished surface (produces images)

yb.Diffuse Reflection reflection off an irregular surface causing light to scatter (no image)

C. Refraction the bending of light that occurs when a light wave passes through a boundary

between two media