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Wave Phenomena 1. Wave Fronts 2. The Doppler Effect 3. Interference of Waves 4. Standing Waves 5. Resonance 6. Diffraction 7. Light Polarization

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Page 2: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Wave Fronts

A wave front is the curve of all adjacent points on a wave that are in phase.

Page 3: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Moving source

Higher frequency, short λLower frequency, longer λ

The Doppler effect can be described as the effect produced by a moving source of waves, the observer, or both –

an apparent upward shift in frequency if the observers and the source is approaching each otheran apparent downward shift in frequency if the observers and the source is moving away from each other.

Relative motion creates an apparent change in frequency.

Doppler Effect

Page 4: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Explaining the Doppler Effect• The Doppler effect is observed because the distance between the

source of sound and the observer is changing. • If the source and the observer are approaching each other, then

the distance is decreasing and the waves is compressed into the smaller distance. The observer perceives sound waves reaching him or her at a more frequent rate (_______ pitch).

• If the source and the observer are moving apart, then the distance is increasing. the waves can be spread apart; the observer perceives sound waves reaching him or her at a less frequent rate (____pitch).

high

low

Page 5: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• It is important to note that both the speed and the frequency of the source does not change.

• The Doppler effect can be observed for any type of wave - water wave, sound wave, light wave, etc.

• car horn - coming and going• As the car approached with its siren blasting, the pitch of

the siren sound (a measure of the siren's frequency) was high; and then suddenly after the car passed by, the pitch of the siren sound was low. That was the Doppler effect - an apparent shift in frequency for a sound wave produced by a moving source.

Page 6: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Shock Waves and Sonic Booms• If a moving source of sound moves at the same speed as

sound or faster than sound, then shock waves will be created and sonic boom is heard.

• http://edweb.sdsu.edu/doppler/elab/elab1.htm

..\..\RealPlayer Downloads\Plane break sound barrier - sonic boom.flv

Page 7: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Blue shift and red shiftThe human eye perceives light waves of different frequencies as differences in color. The lowest frequency we can see is red and the highest frequency we can see is blue-violet.Due to Doppler effect, the apparent color of an approaching light source is shifted toward the blue end of the spectrum, while that of a receding source is shifted toward the red end.

Page 8: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Applications of the Doppler Effect• Police work – the speed of a car is determined by a radar system.

– when a car is at rest, the sent out frequency is the same as received frequency.

– If the car is moving toward the source of radar, the reflected waves have higher frequency, the greater the car’s speed, the greater the Doppler shift in frequency.

– If the car is moving away from the source of radar, the reflected waves have lower frequency.

• Weather stations – Doppler radars are used to determine the location and intensity of precipitation as well as directions and speed of the winds blowing around rain drops.

Page 9: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example

1. A police officer's stationary radar device indicates that the frequency of the radar wave reflected from an automobile is less than the frequency emitted by the radar device. This indicates that the automobile is

a. moving toward the police officer b. moving away from the police officer c. not moving

Page 10: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

example

2. The diagram shows radar waves being emitted from a stationary police car and reflected by a moving car back to the police car. The difference in apparent frequency between the incident and reflected rays is an example of

a. constructive interference b. refraction c. the Doppler effect d. total internal reflection

Page 11: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

3. As observed from the Earth, the light from a star is shifted toward lower frequencies. This is an indication that the distance between the Earth and the star is

a. decreasing b. increasing c. Constant

4. Suppose you are standing on the passenger-loading platform of the commuter railway line. As the commuter train approaches the station, what pitch or changes in pitch will you perceive as the train approaches you on the loading platform?

Page 12: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Wave Interference• A phenomenon which occurs when two WAVES MEET while

traveling along the same medium. • The interference of waves causes the medium to take on a

shape which results from the SUPERPOSITION of the two individual waves.

The two waves meet, produce a net resulting shape of the medium, and then CONTINUE on doing what they were doing before the interference.

Page 13: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Constructive interference• Occurs where the two interfering waves have a displacement in

the same direction. The result is a LARGER AMPLITUDE.

2 units1 unit

-2 units-1 unit

MAXIMUM constructive interference occurs when the waves are in PHASE (phase difference is 0o or 360o) and crest superposes on crest or trough on trough.

The point of maximum displacement of a medium when two waves are interacting is called an ANTI-NODE.

Page 14: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Destructive interference• Occurs where the two interfering waves have a displacement in

the opposite direction. Destructive interferences result a SMALLER amplitude.

• Maximum destructive interference occurs when two waves of equal frequency and amplitude whose phase difference is 180o or ½ λ meet at a point. Maximum destructive interference results in the formation of NODES. Which are regions of ZERO displacement of the medium

Page 15: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Constructive Destructive

Page 16: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

principle of superposition• When two waves interfere, the resulting displacement

of the medium at any location is the ALGEBRAIC SUM of the displacements of the individual waves at that same location.

Displacement of Pulse 1

Displacement of Pulse 2 =

Resulting Displacement

+1 +1 =

-1 -1 =

+1 -1 =

+1 -2 =

+2

-2

0

-1

Page 17: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Two sources in phase in the same medium• ..\..\RealPlayer Downloads\Wave Motion Interference - You

Tube.flvConstructive interference: Point A, B are anti-nodes

Destructive interference: Point C, D, E, F are nodes

crests

troughs

Nodal lines

Page 18: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• Although both sources are repeatedly producing waves which move across the medium, a stable pattern is set up. The regions of constructive interference do not move, nor do the regions of destructive interference.

• These motionless regions have a pattern which can be measured. These measurements can be used to calculate the wavelength of the waves which are producing the pattern. In this way one can find the wavelength of a moving wave.

Page 19: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example #1Determine type of interference of each section as constructive or destructive.

I

II

III

Page 20: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example #2

Apply superposition principle to determine result of interference by sketch the resultant wave.

Page 21: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example1. Two waves having the same amplitude and the same

frequency pass simultaneously through a uniform medium.  Maximum destructive interference occurs when the phase difference between the two waves is

a.   0° c.  90°

b.   180° d. 360°

2. The diagram shows two pulses, each of length, traveling toward each other at equal speed in a rope. Which diagram below best represents the shape of the rope when both pulses are in region AB?

a.

b.

c.

d.

Page 22: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

3. Maximum constructive interference between two waves of the same frequency could occur when their phase difference is

a. 1λ b. ¼ λ c. ½ λ d. 1 ½ λ

4. The diagram below represents shallow water waves of wavelength λ passing through two small openings, A and B, in a barrier. How much longer is the length of path AP than the length of path BP?

a. 1λ b. 2λ c. 3λ d. 4λ

Page 23: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

8. Determine the interference pattern

Page 24: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Sound Interference and Beats• When sound waves meet, interference occurs. The interference

causes the medium to take on a shape which results from the net effect of the two individual waves upon the particles of the medium.

• Constructive interference occurs if compression meets up with compression and rarefaction meets up with rarefaction (in phase). Constructive interferences produce a anti-node, results a louder sound.

• Destructive interference occurs if compression of one wave meets the rarefaction of another wave (out of phase). Destructive interference produce a node, results no sound at all. It is used in noise reduction systems.

• ..\..\sound_en.jar

Page 25: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Musical Beats• When sound waves with slightly different frequencies traveling in

the same direction, the effect of interference is perceived as a variation in loudness, called beats.

• Note: the diagrams represents a sound wave by a sine wave. Because the variations in pressure with time take on the pattern of a sine wave. Sound is not a transverse wave, sound is a longitudinal wave.

Page 26: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• The beat frequency refers to the number of beats per second. For example, if two complete cycles of high and low volumes are heard every second, the beat frequency is 2 Hz. The beat frequency equals to the difference in frequencies of the two interfering notes.

• For example, if two sound waves with frequencies of 256 Hz and 254 Hz are played simultaneously, a beat frequency of 2 Hz will be detected.

• http://www.phys.unsw.edu.au/jw/beats.html#sounds• http://www.acoustics.salford.ac.uk/feschools/waves/super3.ht

m#beats

Beat frequency

Page 27: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Interference of monochromatic light waves• When two same color light sources meet while traveling along the

same medium, Bright and dark bands appear on the screen as a result of interference.

• Constructive interference results in bright band, produced by two interfering waves have a displacement in the same direction.

• Destructive interference results in dark band, produced by two interfering waves have a displacement in the opposite direction.

Page 28: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Thin Film Interference• Another example of light interference is colorful soap bubbles

or streaks of color in a thin film of oil resting on a driveway.

Page 29: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Standing Waves• Standing wave is A WAVE PATTERN that results when two waves of

the SAME frequency, wavelength, and amplitude travel in OPPOSITE DIRECTIONS and interfere.

• A standing wave pattern is formed as the result of the perfectly timed interference of two waves passing through the same medium. A standing wave is NOT actually A WAVE; rather it is the PATTERN.

Page 30: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Nodes and anti-nodes in a standing wave

Nodes: the points of ZERO displacement of the resultant wave

Antinotes: the points of MAXIMUM displacement of a medium

The distance between two successive nodes is ½ λ

standingWaveDiagrams1/StandingWaveDiagrams1.html

Page 31: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• Standing wave patterns are only created within the medium at SPECIFIC FREQUENCIES OF VIBRATION. These frequencies are known as HARMONICS.

• ..\..\RealPlayer Downloads\Standing Wave on a String.flv

• Standing waves can be created for both transverse and longitudinal waves.

• pipe-waves.html

1st harmonic

2nd harmonic

3rd harmonic

Page 32: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Harmonic# of

Nodes # of Antinodes Pattern λ

1st 2 1

                                                      

2L

2nd

                                                      

L

3rd

                                                      

2/3 L

4th

                                                      

½ L

5th

                                                      

2/5 L

6th

                                                      

1/3 L

nth n + 1 n --

Page 33: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Standing waves in water• Standing waves in water are produced most

often by periodic water waves REFLECTING FROM A BARRIER.

Page 34: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example #1

• What is the number of nodes and antinodes in the standing wave shown in the diagram?

8 nodes

7 antinodes

Page 35: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example #2The diagram represents a wave moving toward the right.                    

Which wave shown below could produce a standing wave with the original wave?

1 2 3 4

Page 36: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Example #3• Two waves traveling in the same medium and

having the same wavelength (λ) interfere to create a standing wave. What is the distance between two consecutive nodes on this standing wave?

1. λ 2. ½ λ3. ¼ λ4. ¾ λ

Page 37: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Forced vibration and resonance

Natural Frequency• Nearly all objects, when hit or struck or plucked or strummed

or somehow disturbed, will vibrate. The frequency or frequencies at which an object tends to vibrate with when disturbed is known as the natural frequency of the object.

..\..\RealPlayer Downloads\Natural Frequency.flv

Page 38: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• If you were to take a guitar string and pluck it, you would hear a small sound; On the other hand, if the string is attached to the sound box of the guitar and you pluck it, the sound produced would be much louder.

• This is because the vibrating string force the bridge of the guitar to vibrate, and the bridge force the sound box to vibrate and the sound box forces air particles inside the box to vibrate. This forced vibrations are called sympathetic vibrations.

• The tendency of one object to force another adjoining or interconnected object into vibratio is referred to as a forced vibration. The forced vibration causes an increase in the amplitude and thus loudness of the sound.

Forced vibration

Page 39: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Vibration at natural frequency produces resonance

• Resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibration.

Condition for resonance: 1. when the frequency of the periodic force

equals to the natural frequency of the object it applied to.

2. The amplitude of the original wave is big enough.

Page 40: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Examples of resonance• A non vibrating tuning fork, having a natural

frequency of 256 Hz, will resonate when a vibrating tuning fork with a natural frequency of 256 Hz is brought near it.

• It is possible for an opera singer to Shattering a glass by maintaining a note with a frequency equal to the natural frequency of the glass.

• Collapse of the Tacoma Narrows Bridge due to high wind induced resonance.

• Pushing a child on the swing with the same rhythm as the swing will make the swing go higher.

Page 41: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Blue Skies• The two most common types of matter present in the

atmosphere are gaseous nitrogen and oxygen. These particles are most effective in _____________________________ portions of the visible light spectrum such as blue and violet light. This scattering process involves the absorption of a light wave by an atom followed by reemission of a light wave in a variety of directions.

• All high frequency light are scattered. However, our eyes are more sensitive to light with blue frequencies. Thus, we view the skies as being blue in color.

Page 42: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

What Makes a Red Sunset? • There are two reasons:1. As the Sun gets lower in the sky, its light is passing through

more of the atmosphere to reach you. Even ________________________________, allowing the reds and yellows to pass straight through to your eyes.

2. The sky appears red because ________

______________________, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows.

Page 43: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• In conclusion, resonance occurs when two interconnected objects share the same vibrational frequency. When one of the objects is vibrating, it forces the second object into vibrational motion. The result is a large vibration. And if a sound wave within the audible range of human hearing is produced, a loud sound is heard.

In conclusion

Page 44: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.

Diffraction

Page 45: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

How much diffraction?• The amount of diffraction is

determined by the how the wavelength and the size of opening of the barrier compare.

• When the opening is comparable to the wavelength, most diffraction occurs

• When the opening is much larger than the wavelength, diffraction is less.

Page 46: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

example

• The diagram shows straight wave fronts passing through an opening in a barrier. This wave phenomenon is called

1. reflection 2. refraction 3. polarization 4. diffraction

Page 47: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

example• The diagram shows a wave phenomenon. The

pattern of waves shown behind the barrier is the result of

1. reflection 2. refraction 3. diffraction 4. interference

Page 48: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

example

• A wave is diffracted as it passes through an opening in a barrier. The amount of diffraction that the wave undergoes depends on both the

1. amplitude and frequency of the incident wave 2. wavelength and speed of the incident wave 3. wavelength of the incident wave and the size of the

opening 4. amplitude of the incident wave and the size of the

opening

Page 49: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Polarization of light waves• Light is a transverse wave that vibrate in different planes. A

light wave which is vibrating in more than one plane is referred to as un-polarized light.

Page 50: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• Polarized light waves are light waves in which the vibrations occur in the same plane.

• The most common method of polarization involves the use of a Polaroid filter. Polaroid filters are made of a special material which is capable of blocking one of the two planes of vibration of an electromagnetic wave. When un-polarized light is transmitted through a polaroid filter, it emerges with one-half the intensity and with vibrations in a single plane; it emerges as polarized light.

Light can be polarized

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Note: a longitudinal wave can not be polarized. Sound wave is a longitudinal wave, sound wave can not be polarized. Only transverse wave can be polarized.

Page 53: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

Applications of PolarizationUsed in sun glasses.• Light reflected from surfaces such as a flat road or

smooth water is generally horizontally polarized. This creates an annoying and sometimes dangerous intensity of light that we experience as glare.

• Polarized lenses contain a special filter that blocks this type of intense reflected light, reducing glare.

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Page 55: Wave Phenomena 1.Wave FrontsWave Fronts 2.The Doppler EffectThe Doppler Effect 3.Interference of WavesInterference of Waves 4.Standing WavesStanding Waves

• Three-dimensional movies are actually two movies being shown at the same time through two projectors.

Polarization and 3D films

http://www.physics.org/article-questions.asp?id=56