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CGP Physics > Section 3-Waves P1 > Flashcards

Section 3-Waves P1 Flashcards

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1
Q

Define Wavelength:

A

Wavelength(λ)

-the distance from one peak to another

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2
Q

Define frequency:

A

Frequency(f)

  • how many complete waves there are per second(passing a certain person)
  • measured in hertz(Hz) [1 Hz is 1 wave per second]
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3
Q

Define Amplitude:

A

-the height of a wave (from rest to crest)

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4
Q

Define speed:

A

Speed(v for velocity)

-how fast the wave goes

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5
Q

Define period:

A

Period(T)

-the time it takes(in seconds) for one complete wave to pass a point

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6
Q

What’s the equation to work out frequency?

A

1
Frequency,f(Hz) = ————————
Time period,T(s)

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7
Q

What’s the equation linking Wavelength, Wave Speed and Frequency?

A

Wave Speed(m/s) = Frequency(Hz) x Wavelength(m)

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8
Q

What are the two types of waves?

A
  • Transverse

- Longitudinal

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9
Q

Define Transverse Waves:

A

In TRANSVERSE waves the vibrations are at 90° to the direction is transferred by the wave.

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10
Q

What’re examples of transverse waves?

A

Most waves are transverse

  • light and all other EM waves
  • slinky spring wiggled up and down
  • waves on strings
  • ripples on water
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11
Q

Define Longitudinal Waves:

A

In LONGITUDINAL waves the vibrations are along the same direction as the wave transfers energy.

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12
Q

What’re examples of Longitudinal Waves?

A
  • sound and ultra sound
  • shock waves
  • slinky spring when you push the end
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13
Q

What ways do Waves transfer energy and information?

A

All Waves transfer energy and information without transferring matter.

  • all Waves carry and transfer energy in the direction they’re travelling
  • Waves can also be used as signals to transfer information from one place to another
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14
Q

What are wavefronts?

A

Wavefronts are imaginary planes that cut across all the waves, connecting the points on adjacent waves which vibrating together.
-the distance between each wavefront is equal to one Wavelength

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15
Q

What’s the Doppler effect?

A
  • Waves produced by a source which is moving towards or away from an observer will appear to have a different Wavelength than they would if the source was staitionary
  • wave speed is constant so if a source is moving it ‘catches up’ to the waves in front of it
  • the frequency of a source moving toward you will seem higher and the wavelength shorter whereas when a source is moving away its opposite(the faster the source is travelling the shorter the wavelength)
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16
Q

What’re the seven types of electromagnetic waves? (In order- increasing in frequency and decreasing wavelength)

A
  • radio waves
  • microwaves
  • infrared
  • visible light
  • ultra violet
  • x-rays
  • gamma rays
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17
Q

What are features of electromagnetic waves?

A
  • electromagnetic waves with different wavelengths have different properties
  • they’re grouped into seven types depending on their wavelength
  • it’s a continuous spectrum
  • all transverse waves and travel at the same speed through a vacuum
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18
Q

What are the different wavelengths in visible light?

A

Different colours have different wavelengths

-red has the longest wavelength(lowest frequency) and violet has the shortest wavelength(highest frequency)

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19
Q

What’s the spectrum of visible light? In order increasing in frequency and decreasing in wavelength

A 
Red (Richard)
Orange (Of)
Yellow (York)
Green (Gave)
Blue (Battle)
Indigo (In)
Violet (Vain)
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20
Q

What’re the uses of radio waves and what’s are the different types of radio waves?

A

Radio waves(wavelength >10cm) are used mainly for communication

  • long-wave radio(wavelength 1-10km) are bent around the surface of the earth, transmitted a long way
  • short-wave radio(wavelength 10-100m) can be received at long distances from the transmitter because they’re reflected from the ionosphere
  • radio waves(wavelength 0.1-1m) used for TV and FM, must be in direct sight of the transmitter
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21
Q

What’re the uses of microwaves?

A

Microwaves(wavelength 1-10cm)

  • satellite communication, a signal from a transmitter is transmitted into space where it’s picked up by a satellite receiver dish the satellite dish then transmits the signal back to earth
  • mobile phone calls
  • microwaves used for cooking, microwaves are absorbed by water molecules in the food these waves only penetrate a few centimetres so the heat is spread out by conduction or convection
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22
Q

What’re uses of infrared(heat) radiation?

A
  • electrical heaters radiate IR to keep us warm
  • grills use IR to heat food
  • IR is given out by all objects(the hotter the more IR)
  • IR can be detected by night-vision equipment, it turns IR into an electrical signal which is displayed on a screen as a picture
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23
Q

How can light signals travel through optical fibres?

A
  • visible light can be used for communication(optical fibres), they carry data as pulses of light
  • optical fibres work by bouncing waves off the sides of a narrow core
  • a pulse of light enters the fibre at a certain angle and reflects along the core
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24
Q

What are uses of visible light?

A
  • increasing used for telephone and broadband internet cables
  • medical purposes to ‘see inside’ the body without having to operate
  • photography, cameras use a lens to focus visible light onto a light-sensitive film or sensor, the aperture(how much light can enter) and the shutter speed(how long the film or sensor is exposed to light)
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25
Q

What’re uses of ultra violet lights?

A
  • fluorescence is a property of certain chemicals where they absorb uv and visible light is emitted
  • fluorescent lights use uv radiation to emit visible light, they’re safe as nearly all the uv radiation is absorbed and they’re more energy efficient than filament light bulbs
26
Q

What’re uses of x-rays?

A
  • X-rays are used to view the internal structure of objects and materials
  • X-ray images are produced by the detector plate determining where fewer X-rays get through(brighter bits)
  • radiographers in hospitals help diagnose broken bones
  • exposure to x-rays can cause mutations which lead to cancer
27
Q

What’re uses of gamma radiation?

A
  • sterilising medical equipment, they kill all microbes and reduces the risk of damaging equipment
  • sterilising food, killing all the microbes and this process keeps food fresher for longer and the food is not radioactive afterwards
28
Q

Can different types of EM radiation have different effects on the body and if so what types?

A

Yes they can have different effects.

  • some just passes through soft tissue without being absorbed (radio waves)
  • for some types radiation is absorbed causing heating of cells (microwaves)
  • some cause cancerous changes in living cells (gamma rays)
29
Q

What’s the trend between the danger of waves and the frequency?

A

The higher the frequency the more dangerous the wave is.

30
Q

How is the body effected by being exposed to microwaves?

A
  • microwaves have a similar frequency to the vibrations of many molecules, so they increase these vibrations
  • resulting in internal heating
  • MICROWAVES HEAT HUMAN BODY TISSUE
  • microwave ovens need to have shielding to protect the user
31
Q

How is the body effected by being exposed to infrared radiation?

A
  • IR frequencies can make surface molecules of any substance vibrate, this has a heating effect
  • higher frequency so more heating, if the human body is exposed to too much it can cause skin burns
  • you can protect yourself by using an insulating material as a barrier
32
Q

How is the body effected by being exposed to ultraviolet?

A
  • UV can DAMAGE SURFACE CELLS and cause BLINDNESS
  • some frequencies of UV are ionising(carry enough energy to knock electrons off), this can cause cell mutation or destruction and cancer
  • wear sunscreen with UV filters and stay out of strong sunlight to protect your skin
33
Q

How is the body effected by being exposed to gamma rays?

A
  • carry the most energy and are ionising resulting in them being the most damaging and can penetrate further into the body
  • CAUSE CELL MUTATION OR DESTRUCTION LEADING TO TISSUE DAMAGE OR CANCER
  • gamma ray sources should be kept in lead lined boxes, and when people have to be exposed to them it should be for the shortest time possible
34
Q

What happens to light when it reflects from an uneven surface (e.g. a piece of paper)?

A
  • the light reflects off at different angles

- so you get a diffuse reflection

35
Q

What happens to light when it reflects from an even surface (e.g. smooth and shiny like a mirror)?

A
  • all the light is reflected at the same angle
  • you get a clear reflection
  • because light bounces of the surface into your eyes
36
Q

What’s the law of reflection:

A

ANGLE OF INCIDENCE = ANGLE OF REFLECTION

37
Q

What’s the normal line on a light diagram?

A
  • the normal is an imaginary line
  • it’s perpendicular to the surface at the point of incidence
  • it’s shown as a dotted line
38
Q

What’s the angle of incidence?

A

-the angle between the incoming wave and the normal

39
Q

What’s the angle of reflection?

A

-the angle between the reflected wave and the normal

40
Q

How do you draw a plane mirror diagram?

A

From the object you draw two rays when the meet the normal you treat the like normal incident and reflected rays NORMAL LINES, then behind the mirror you repeat the two incident rays just on the opposite side of the mirror BUT USE DASHED LINES

41
Q

What’re virtual images?

A

Virtual images are formed when the light rays bouncing off an object onto a mirror are diverging.

42
Q

Why do waves travel at different speeds in different substances?

A

Different substances have different densities

-light waves generally travel slower in denser substances

43
Q

What happens to a wave when it crosses into another substance?

A

It changes speed

44
Q

What happens if a light wave hits a different substance at 90°?

A

The wave changes speed but carries on in the same direction

45
Q

What happens if a wave hits a different medium at a non perpendicular angle?

A

-the part of the wave that hits the denser medium first slows down
-whilst the other part carries on a little longer at the faster speed so the wave changes direction
THE WAVE HAS BEEN REFRACTED

46
Q

What’s a ray diagram?

A

A diagram that shows you the path that a wave travels

Rays are drawn as straight lines

47
Q

How do you draw a ray diagram?

A

Draw the normal, then draw the incident ray which meets the normal, the draw the refracted ray(if the object is denser the angle should be smaller if the object is less dense the angle should be larger)

48
Q

Describe a practical for rays passing through a rectangular glass block when it’s refracted twice:

A
  • use a rectangular block of a particular material resting on a piece of paper
  • shine a light ray at an angle into the block, some light is reflected but most passes through the glass and gets refracted as it does so
  • you trace the incident and emergence ray and draw in the refracted ray by joining the two line
  • then label the incident ray, angle; refracted ray, angle and emergence ray, angle
49
Q

In a practical for rays passing through a rectangular glass block when it’s refracted twice, which two angles are equal?

A

Angle of incidence = angle of emergence

50
Q

What do triangular prisms do?

A

They disperse light

51
Q

Why do triangular prisms disperse light?

A

Different wavelengths of light refract by different amounts so white light(which is a mix of all visible frequencies) disperses into different colours as it enters a prism and the different wavelengths are refracted by different amounts. A similar effect happens when the light leaves the prism which means you get a rainbow.

52
Q

What does the refractive index of a material tell you?

A

How fast light travels in that medium

53
Q

Define refractive index:

A

speed of light in a vacuum(c)
refractive index(n) = ———————————————
speed of light in that material(v)

54
Q

What’s Snell’s law?

A

sin i
n = —————
sin r

55
Q

Describe a practical to refractive index of glass using a glass block:

A
  • draw round a rectangular glass block and direct a light through it at different angles such as 20,30,40,50,60 working out the angle of refraction for all of these
  • then plot a graph of sin i against sin r and the gradient is the refractive index
56
Q

Describe a practical which uses a semicircular block to show total internal reflection:

A
  • draw round the glass block, aim the incident ray at the glass block so that the light enters at 90° this means it doesn’t bend when it enters the block only when it leaves the block
  • as you increase the incident angle the refraction angle gets closer to 90°
  • eventually i reacher 90° this is known as the critical angle
  • record your results in a table
57
Q

What happens if the angle of incidence is less than the critical angle?

A

Most of the light passes out but a little bit is internally reflected

58
Q

What happens if the angle of incidence is equal to the critical angle?

A

The merging ray comes out along the surface, there’s more internal reflection

59
Q

What happens if the angle of incidence is greater than the critical angle?

A

No light comes out, it’s all internally reflected

TOTAL INTERNAL REFLECTION

60
Q

What’s the equation to work out the critical angle?

A

1
sin C = ——
n

61
Q

How do optical fibres use total internal reflection?

A
  • Optical fibres are made of plastic or glass and consist of a central core surrounded with a lower refractive index
  • the core of the fibre is so narrow that light signals passing through always hit the core cladding at an angle higher than C so the light is TIR
  • it only stops working if the fibre is bent to sharply
62
Q

How do prisms use total internal reflection?

A
  • total internal reflection allows us to see objects that aren’t directly in our line of sight. This is how periscopes work
  • the ray of light travels into a prism where it’s TIR by 90°
  • it then travels to another prism lower down and is TIR by another 90°
  • the ray is now travelling parallel to its initial path but at a different height

CGP Physics (16 decks)

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