Waves

Introduction to Wave pt 3: EM vs Mechanical Waves

Multiple Choice

1. What property of a wave is represented by letter A?

• A. Wavelength

• B. Amplitude

• C. Speed

• D. Frequency

Multiple Choice

2. What property of a wave is represented by letter B?

• A. Wavelength

• B. Amplitude

• C. Speed

• D. Frequency

Multiple Choice

3. What property of a wave is represented by letter C?

• A. Wavelength

• B. Amplitude

• C. Speed

• D. Frequency

Multiple Choice

4. What part of a wave is represented by letter D?

• A. Crest

• B. Compression

• C. Rarefaction

• D. Trough

Multiple Choice

7. Which of the following occurs as the frequency of a wave decreases?

• A. The wavelength increases
• B. The wavelength decreases
• C. The wavelength increases and then decreases
• D. The wavelength remains the same

Multiple Choice

16. The highest part of a transverse wave is known as a ____________________.

• Crest
• Trough
• Compression
• Rarefaction
• Medium

​Types of Waves

• Waves may be categorized based on whether or not they need a medium.

• ​There are two types of waves:

  • 1.) Mechanical waves: require a medium (matter) to travel.

    2.) Electromagnetic (EM) waves: do NOT require a medium to travel.

​Mechanical waves

• ​These require a medium for the vibrations to travel and so cannot travel through space (vacuum)

• ​

• ​May either move as transverse or longitudinal waves.

• ​

• ​Ex. sound, water wave, slinky,

​​Mechanical waves

• ​The speed at which they travel depends on either the type of wave or the medium they are in.

• ​

• ​They travel fastest in more dense medium. Therefore, they move fastest in solids and slowest in gases.

• ​

• ​Generally, these have longer wavelengths than electromagnetic waves.

​Electromagnetic Wave

• ​A waves that does NOT require a medium (matter to travel), has an electric field component and a magnetic field component.

​

• ​These two fields move perpendicular to the propagation of the wave and so they are all transverse waves

​Electromagnetic waves

• ​All electromagnetic waves travels at the speed of light 3.0 x 10⁸ m/s in a VACUUM. However, they travels at different speeds when traveling through matter.

• They travel fastest in less dense medium, so fastest in gases and slowest in solids.

• Ex: Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, and Gamma Ray.

​Electromagnetic Spectrum

• ​Shows a visual display of various electromagnetic waves to compare their relative wavelengths and frequencies.

Multiple Choice

Which type of waves must have a medium in order to travel?

• electromagnetic wave

• mechanical wave

Multiple Choice

Mechanical waves usually travel fastest through:

• solids

• liquids

• gases

Multiple Choice

Which type of waves must have a medium in order to travel?

• electromagnetic wave

• mechanical wave

Multiple Choice

Wave with the longest wavelength

• microwave
• radio
• gamma
• visible light

Multiple Choice

When the wavelength increases the frequency will

• increase

• decrease

• remain same

• none of these

Multiple Choice

EM waves  

• Must travel through a vacuum
• Can travel through a medium or a vacuum
• Are the same type of wave as mechanical waves
• Can only travel through a vacuum

Multiple Choice

All electromagnetic waves have the same...

• frequency
• speed
• wavelength
• energy

Multiple Choice

When a wave is travelling through matter, what happens to the matter?

• The matter is pulled along behind the wave as that makes it a longitudinal wave.

• The wave is making the matter move back and forth as that will make a transverse wave.

• The wave is making the matter move up and down.

• The matter is pulled along behind the wave as that makes it a compressional wave.

• The matter does not move along with the wave.

Multiple Choice

It depends on the medium in which the wave is traveling. It varies in solids, liquids and gases.

• Frequency

• Wave speed

• Amplitude

• Wavelength

Multiple Choice

Which wave in the diagram has the greatest wavelength?

• 1

• 2

• 3

• 4

Wave Properties

​

Wave Interactions

Let's see what we know...

Parts of a Wave

Amplitude, Wavelength, Frequency, Wave Speed

All waves have these properties, regardless of their classification

Multiple Choice

What type of wave interaction is described by the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through?

• Reflection

• Refraction

• Diffraction

• Interference

Amplitude

• Amplitude is the maximum distance the particles vibrate from the rest position.

• Rest position is the place where the particles of a medium stay when there is no disturbance. The taller the wave = larger amplitude

• The taller the wave = larger amplitude

Multiple Choice

A water wave is an example of what type of wave?

• electromagnetic wave

• mechanical wave

Poll

If a wave has a small amplitude, do you think it has low energy or high energy?

• Low energy

• High Energy

Multiple Choice

The angle of incidence (incoming ray) will always equal the ray of reflection (outgoing ray).

• True

• False

Amplitude & Energy

• Small amplitude = low energy

• Large amplitude = high energy

Multiple Choice

What type of interaction is described a the bending of a wave as it passes at an angle from one medium to another?

• Reflection

• Refraction

• Diffraction

• Interference

Measuring Amplitude on a Transverse Wave

• Measured from the rest position to the crest or trough of the wave

Measuring Amplitude on a Longitudinal Wave

• It is difficult to show amplitude on this wave.

• Amplitude of a longitudinal wave is related to how tightly packed the compressions are.

• The tighter the packing = greater amplitude

Wavelength

• Wavelength is the distance from any point on a wave to an identical point on the next wave

Multiple Select

What changes as a wave passes through a new medium?

• Speed

• Wavelength

• Amplitude

• Direction of the wave

Wavelength on Transverse Waves

• The distance between two adjacent crests

• OR the distance between two adjacent troughs

Multiple Choice

What wave interaction is described as the bending of a wave as it moves around an obstacle or passes through a narrow opening?

• Reflection

• Refraction

• Diffraction

• Rarefaction

Wavelength on Longitudinal Waves

• The distance between two adjacent rarefactions

• OR the distance between two adjacent compressions

Wavelength & Energy

• The shorter the wavelength the greater the energy

• OR the longer the wavelength the lower the energy

• They are inversely proportional

• The symbol for wavelength is the Greek letter lamda--> λ

Frequency

• The number of vibrations (waves, cycles) that occur per second

• Unit is Hertz (Hz)

• 1 Hz = one wave per second

• High frequency carry high energy

Multiple Choice

There is _______ relationship between the size of the opening a wave passes through and the amount of diffraction it experiences.

• no apparent

• a direct

• an indirect

Frequency in Transvese Waves

• Frequency is measured by the number of crests OR troughs that pass a certain point over a certain amount of time

Multiple Choice

What type of wave interaction is the interaction between waves that meet and overlap?

• Reflection

• Transmission

• Transmutation

• Interference

Frequency in Longitudinal Waves

• To find the frequency, count the number of compressions or rarefactions.

Multiple Choice

Which wave carries more energy?

• Wave A

• Wave B

Wave Speed

• Wave speed is the speed at which a wave travels

• The speed depends on the medium in which the wave is traveling

• Wave speed = wavelength x frequency

Multiple Choice

Which type of interference would result if waves A & B overlapped?

• Constructive interference

• Destructive interference

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Multiple Choice

What type of interaction does this picture represent?

• Reflection

• Interference

• Refraction

• Diffraction

Doppler Effect

Learning Outcomes

• State the Doppler Effect

• Be able draw the Doppler effect

• Give examples

• Explain in terms of frequency

Multiple Choice

What can you tell about this object's motion?

• Moving to the North (up).
• Moving to the South (down). 
• Moving to the West (left). 
• Moving to the East (right). 

Multiple Choice

What can you tell about the motion of this object?

• Moving left.
• Moving right quickly.
• Standing still. 
• Moving up slowly. 

Multiple Choice

The vast majority of galaxies in our universe are moving away from us.  We know this because we observe __________ in the galaxies absorption spectra.

• Redshift
• Blueshift
• Turbulance
• Superposition

Multiple Choice

If a star is being observed from Earth and it's light has shifted towards the blue side of the electromagnetic spectrum it would be...

• Moving towards the Earth
• Moving away from the Earth
• This is a trick question that cannot be answered
• It isn't a star, it is a very large blueberry.

Multiple Choice

What best describes the doppler effect?

• An apparent change in frequency of a wave due to the relative motion between a wave source and an observer
• When sound changes pitch
• When light changes color
• An apparent change in the amplitude of a wave due to the relative motion between a wave source and an observer.

Multiple Choice

The Doppler effect is seen when a wave-making source moves toward an observer. 

• True
• False

Multiple Choice

When an ambulance move TOWARD you it sounds ________ pitched. 

• high
• low
• medium

Multiple Choice

When the car moves AWAY from you, its horn seems...

• Low pitched
• High pitched
• Normal

Multiple Choice

Short sound waves are...

• high pitched
• low pitched
• medium pitched

Multiple Choice

Long sound waves are...

• high pitched
• low pitched
• medium pitched

Multiple Choice

Sound does not travel in space because

• Space is too far away.
• There is no matter in space.
• Space is the final frontier
• Space has planets.

Multiple Choice

Roughly what is the speed of sound in water?

• About 350 m/s

• About 1 500 m/s

• About 5000 m/s

• About 1800 m/s

Multiple Choice

Roughly what is the speed of sound in air?

• The speed of light.

• About 10 m/s

• About 340 m/s

• About 1 500 m/s

Multiple Choice

Why does sound travel faster in solids than in liquids or gases.

• They are harder.

• The particles are closer together.

• Solids have more energy.

• Gases fill their container.

Multiple Choice

Which state of matter do sounds travel fastest in?

• Solid

• Liquid

• Gas

• Plasma

Multiple Choice

Which factor does not affect the speed of sound:

• temperature
• distance
• density
• elasticity

Poll

How are you at stating the Doppler Effect

• Very confident

• Okay

• Not sure

• Not a clue

Poll

How are you at giving examples of the Doppler effect?

• Very confident

• Okay

• Not sure

• Not a clue

Poll

How are you at explaining frequencies?

• Very confident

• Okay

• Not sure

• Not a clue