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Physics > 3) Waves > Flashcards

3) Waves Flashcards

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1
Q

Two types of waves

A

-transverse
-longitudinal

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2
Q

Transverse waves

A

-waves that vibrate or oscillate perpendicular to the direction of energy transfer (wavy line)
-peak/ crest - highest point
-trough - lowest point
-e.g. ripples on water, vibrations in a guitar string, s-waves, electromagnetic (radio, light, x-rays)

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3
Q

Transverse waves features

A

-energy transfer is the same direction as the wave motion
-can move in a liquid or solid, not a gas
-some (electromagnetic waves) can move in a vacuum
-constant density, pressure

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4
Q

Longitudinal waves

A

-Waves where the points along its length vibrate parallel to the direction of energy transfer (like a spring)
-compressions - close together
-rarefactions - space apart
-represented by sets of lines
-e.g. sound waves, p-waves, pressure waves caused by repeated movements in a liquid or gas

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5
Q

Longitudinal waves features

A

-The energy transfer is in the same direction as the wave motion
-They can move in solids, liquids and gases
-They can not move in a vacuum (since there are no particles)
-changes in density, pressure

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6
Q

Waves & energy

A

-waves transfer energy and information, not matter
-described as oscillations or vibrations about a fixed point
-all waves can be refracted, reflected

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7
Q

Amplitude

A

The distance from the undisturbed position to the peak or trough of a wave
-Symbol A
-measured in metres

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8
Q

Wavelength

A

The distance from one point on the wave to the same point on the next wave
-transverse: measured one peak to the next
-longitudinal: measured from centre of one compression to the centre of the next
-symbol λ (lambda)
-measured in metres

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9
Q

Frequency

A

The number of waves passing a point in a second
-Symbol f
-measured in Hertz (Hz)

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10
Q

Time period

A

The time taken for a single wave to pass a point
-Symbol T
-measured in seconds (s)

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11
Q

Calculate wave speed

A

-wave equation
Wave speed (m/s) = frequency(Hz) x wavelength(m)
v=fλ

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12
Q

Calculate frequency

A

Frequency (Hz) = 1/Period (s)
f=1/T

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13
Q

The Doppler effect

A

The apparent change in wavelength and frequency of a wave emitted by a moving source
-when a stationary object emits waves, waves spread out symmetrically
-when object begins to move, the waves can get squashed together at one end, and stretched at the other
-squashed together - wavelength decreases, frequency increases - higher pitch
-stretched out - wavelength increases, frequency decreases - lower pitch

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14
Q

Electromagnetic waves

A

Transverse waves that transfer energy from the source of the waves to an absorber
-all transverse
-all travel through a vacuum
-all travel at the same speed in a vacuum

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15
Q

Electromagnetic spectrum

A

Lower energy, long wavelength, low frequency
-radio waves
-microwaves
-infrared
-visible light
-ultraviolet
-x-rays
-gamma rays
Higher energy, short wavelength, high frequency
Raging Martians Invaded Venus Using X-ray Guns

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16
Q

Electromagnetic spectrum - radiation

A

-higher the frequency, higher energy of radiation
-radiation with higher energy: highly ionising, harmful to cells and tissues causing cancer
-radiation with lower energy: useful for communication, less harmful for humans

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17
Q

Visible light

A

-the range of wavelengths which are visible to humans (only part of spectrum)
-each colour corresponds to a narrow band of wavelength and frequency
-Red: longest wavelength, lowest frequency and energy
-Violet: shortest wavelength, highest frequency and energy

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18
Q

Radiowaves use

A

-communication (radio and TV)
-broadcasting

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19
Q

Microwaves use

A

-heating food
-satellite transmission
-communication (WiFi, phones)

20
Q

Infrared use

A

-heaters
-night vision equipment
-remote controls

21
Q

Visible light use

A

-optical fibres
-photographs

22
Q

Ultraviolet use

A

-fluorescent lamps
-suntan

23
Q

X-rays use

A

-observing the internal structure of objects and materials (medical applications, airport security)

24
Q

Gamma rays use

A

-sterilizing medical instruments/ food
-treating cancer

25
Q

Microwaves - danger

A

-high intensity microwaves can cause heating of internal organs
-as water molecules absorb microwaves strongly

26
Q

UV waves - danger

A

-if eyes exposed to high levels - severe eye damage
-ionizing - can kill cells, cause them to malfunction
-premature ageing - skin cancer

27
Q

Light waves

A

-visible light is part of the electromagnetic spectrum - transverse wave
-can undergo reflection, refraction

28
Q

Sound waves

A

-vibrations of air molecules - longitudinal wave
-When a sound wave comes into contact with a solid those vibrations can be transferred to the solid

29
Q

Reflection

A

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

30
Q

Refraction

A

A wave passes a boundary between two different transparent media and undergoes a change in direction

31
Q

Angle of incidence vs reflection

A

-angle of incidence: angle of the wave approaching the boundary
-angle of reflection: angle of the wave leaving the boundary
-angles measured between the wave direction and a line 90 degrees to the boundary

32
Q

The Law of Reflection

A

Angle of incidence (i) = Angle of reflection

33
Q

Refraction - density of materials

A

-from less dense to more dense: light bends towards the normal - rays slow down
-more dense to less dense: light bends away from the normal
-pass along the normal (perpendicular): light doesn’t bend

-frequency of waves do not change

34
Q

Practical: investigating the refraction of light

A
  1. trace around glass object using a pencil
  2. direct a beam of light at the side face of the block
  3. mark point on ray close to the block and point on the exit light ray
  4. mark where the ray enters and exits the block
  5. connect points
  6. repeat process for the ray at a different angle
  7. repeat the procedure for each shape of block (semi-circular, prism)
35
Q

Snells’ Law

A

-less dense –> more dense - i>r
-more dense –> less dense - i<r
n = sin i/ sin r
n = refractive index = speed of light in vacuum/ speed of light in material

36
Q

Critical angle

A

-the angle of incidence when angle of refraction is exactly 90
-light is refracted along the boundary

37
Q

Total internal reflection

A

Occurs when:
-the angle of incidence > the critical angle
The light ray moves from a more dense medium to a less dense medium

38
Q

Total internal reflection - optical fibres

A

-consists of very thin core of high purity glass covered by a second layer of less dense high purity glass
-light passing along the core at the angle greater than the critical angle are totally internally reflected
-acts like a mirror, light ray continuously reflected along the length of the optical fibre core

39
Q

Total internal reflection - prisms

A

Light is internally reflected by 90 degrees

40
Q

Calculating critical angle

A

sin c = 1/n
-large refractive index, smaller critical angle
-light rays inside a material with a high refractive index are more likely to be totally internally reflected

41
Q

Frequency range for human hearing

A

20-20000 Hz

42
Q

Practical: investigate the speed of sound in air

A
  1. Have two people 100m between each other
  2. One person bangs wooden blocks together to generate sound
  3. Second person have a stopwatch, start when they see person banging blocks, stop when they hear the sound
  4. Repeat, average taken
  5. Calculate speed = distance/ time
43
Q

How oscilloscope and microphone used to display a sound wave

A

-microphone plugged into oscilloscope
-sound into microphone
-microphone will transfer sound into electrical signal
-oscilloscope displays signal

-x-axis - time
-y-axis - height of wave

44
Q

Practical: investigate the frequency of a sound wave using an oscilloscope

A
  1. Connect microphone to oscilloscope
  2. adjust time base of oscilloscope until signal fits onto screen
  3. Strike tuning fork, hold near mic
  4. Freeze/ take a picture of oscilloscope screen
  5. Measure, record time period of wave signal by counting number of divisions for one complete wave cycle
  6. Repeat steps 3-5 with different tuning forks
45
Q

Pitch relative to frequency

A

-high frequency, high pitch
-low frequency, low pitch

Physics (8 decks)

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