P6 Flashcards

1
Q

What is a transverse wave?

A

waves that oscillate perpendicular to the direction of energy transfer

e.g. light waves, EM waves, ripples on water

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2
Q

What is a longitudinal wave?

A

waves that oscillate parallel to the direction of energy transfer

e.g. sound wave, ultrasound

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3
Q

What is the amplitude?

A

the maximum displacement of a point on the wave from its undisturbed position

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4
Q

What is the wavelength?

A

the distance from a point on one wave to the same point on the adjacent wave

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5
Q

What is the frequency?

A

the number of waves passing a point each second

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6
Q

How do you calculate the time period of a wave?

A

T= 1/f

T= period (s)

f= frequency (Hz)

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7
Q

What is the definition of wave speed?

A

the speed at which energy is being transferred through the medium

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8
Q

What is the equation for wave speed?

A

v = f λ

wave speed= frequency x wavelength

v= m/s

λ= m

f= Hz

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9
Q

What are the two different types of waves?

A

Mechanical- waves which require a medium to travel through
- can be transverse or longitudinal

Electromagnetic- waves that do not require a medium to travel through
- always transverse

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10
Q

How can you measure the speed of sound waves in air?

A

Using an oscilloscope- by attaching a signal generator to a speaker you can generate sounds with a specific frequency and use two microphones and oscilloscope to find the wavelength

  1. Set up the oscilloscope so that the detected waves at each microphone are shown as separate waves
  2. start with both microphones next to the speaker and then slowly move one away until the two waves are aligned on the oscilloscope display but have moved 1 wavelength apart
  3. measure the distance between the microphones to find one wavelength
  4. use the formula wave speed = frequency x wavelength to find the speed of sound waves passing through the air
  5. the frequency is whatever you set the signal generator to
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11
Q

How can you measure the speed of ripples on a water surface?

A

Using a ripple tank (a shallow tray with a clear bottom)

  1. use a power pack and set the voltage, this makes the dipper vibrate and produces the frequency
  2. to find the wavelength, take a photograph of the wave with the ruler in the shot
  3. to find the frequency record a video for 10 secs and play it back in slow-mo
  4. Then pick a point and count the number of waves that pass that point in the given time and divide it by 10
  5. to calculate wave speed= frequency x wavelength
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12
Q

What can happen to wave once it meets the boundary between two different materials?

A

It can be refracted or reflected or absorbed

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13
Q

What is reflection?

A

When a wave bounces off a medium after meeting a boundary between two media

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14
Q

What are the two different types of reflection?

A

Specular: when a wave is reflected in a single direction by a smooth surface e.g. a mirror

Diffuse: when a wave is reflected by a rough surface and the reflected rays are scattered and in lots of different directions

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15
Q

What is refraction?

A

When a wave changes direction as it crosses the boundary between two media at an angle to the normal

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16
Q

What effect does the optical density of a material have on the speed of light through it?

A

The higher the optical density, the slower light waves travel through it

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17
Q

What is the critical angle?

A

The angle at which the angle of incidence causes the refracted ray to be at 90 degrees to the normal

  • only happens from more optically dense to less optically dense
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18
Q

What is the total internal reflection?

A

When the angle of incidence is greater than the critical angle

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19
Q

What do sound waves travel through the air as?

A

Sound travels through the air as a series of compressions and rarefactions

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20
Q

What are compressions?

A

Regions of high pressure, the particles are close together

21
Q

What are rarefactions?

A

regions of low pressure, the particles are spread further apart

22
Q

How do we hear sounds?

A
  • As the speaker vibrates, it meets air particles and the air particles experience a pressure change and begin to vibrate
  • the series of vibrations pass the sound wave to the ear
  • sound waves of a certain frequency reach your eardrum and cause it to vibrate
23
Q

What is the human hearing range?

A

20 Hz to 20 kHz (20000Hz)

(this is limited to the size and shape of our eardrums and the structure within the ear)

24
Q

What happens to sound wave as it enters a denser medium?

A

its velocity (wave speed) increases whilst its frequency remains constant and the wavelength increases

25
Q

What is ultrasound?

A

a sound wave with a frequency greater than 20 kHz (above the human hearing range)

26
Q

What is infrasound?

A

sound waves below 20Hz

27
Q

How do ultrasounds work?

A

ultrasound waves are partially reflected when they meet a boundary between two media. The time taken for the reflections to reach a detector can be used to determine how far away a boundary is (using distance= speed x time)

28
Q

Give uses of ultrasounds

A
  • industrial imaging (finding cracks in pipes)
  • medical imaging (prenatal scanning)
  • echo sounding (to determine the depth of the water below)
29
Q

What are produced when there is an earthquake?

A

Seismic waves which travel through the Earth and carry away energy from the earthquake

30
Q

Describe P-waves

A

• are longitudinal waves
• can pass through both solids and liquids
• travel faster than S-waves

31
Q

Describe S-waves

A

• transverse waves
• cannot travel through a liquid; only solids
• slower than P-waves

32
Q

How do we know about the structure of the Earth?

A

P-waves and S-waves provide evidence for the structure and the size of the Earth’s core

• S-waves are not able to pass through liquids and consequently they do not pass through the outer core, which suggests that there is a liquid iron structure within the Earth

33
Q

What are electromagnetic waves?

A

Transverse waves that transfer energy from the source of waves to an absorber

34
Q

List the electromagnetic spectrum from longest wavelength to shortest.

A
  1. Radio waves
  2. Microwaves
  3. Infrared radiation
  4. Visible light
  5. Ultraviolet
  6. X-rays
  7. Gamma rays
35
Q

What speed do EM waves travel at (in a vacuum)?

A

3 x 108

36
Q

What happens when radio waves are absorbed?

A

They may create an AC with the same frequency as the radio wave

37
Q

What EM waves can have hazardous effects on human body temperature?

A

ultrasound waves, X-rays, gamma rays

38
Q

What is radiation dose?

A

a measure of the risk of harm resulting from an exposure of the body to the radiation

39
Q

What is radiation measured in?

A

Sieverts

40
Q

What are uses of electromagnetic waves?

A

• radio waves – television and radio
• microwaves – satellite communications, cooking food
• infrared – electrical heaters, cooking food, infrared cameras
• visible light – fibre optic communications
• ultraviolet – energy efficient lamps, sun tanning
• X-rays and gamma rays – medical imaging and treatments

41
Q

How does a lens form an image?

A

by refracting light

42
Q

What are the two types of lenses?

A

Convex - image produced is either real or virtual

Concave - image produced is always virtual

43
Q

How do colour filters work?

A

By absorbing certain wavelengths and transmitting other wavelengths

44
Q

How is the colour of an opaque object determined?

A

By which wavelengths of light are more strongly reflected

  • If all wavelengths are reflected equally the object appears white
  • If all wavelengths are absorbed the object appears black
45
Q

What is a perfect black body?

A

an object that absorbs all of the radiation incident on it; it does not reflect or transmit any radiation

  • it would be the best possible emitter
46
Q

What do all bodies (objects) emit and absorb?

A

Infrared radiation

  • the hotter the body, the more infrared radiation it radiates in a given time
47
Q

Explain what is happening to a body at constant temperature

A

It is absorbing radiation at the same rate as it is emitting radiation

  • the temperature of a body increases when the body absorbs radiation faster than it emits radiation
48
Q

What does the temperature of the Earth depend on?

A
  • the rates of absorption and emission of radiation
  • reflection of radiation into space