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waves Flashcards

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1
Q

EM wave spectrum from lowest to highest frequency

A

radio, microwaves, IR, visible, UV, X-ray, gamma

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2
Q

uses of radio waves

A

broadcasting and communications

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3
Q

uses of microwaves

A

cooking and satellite transmissions

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4
Q

uses of infrared waves

A

heaters and night vision equipment

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5
Q

uses of visible light

A

optical fibres and photography

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6
Q

uses of ultraviolet waves

A

fluorescent lamps

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7
Q

uses of x-rays

A

observing the internal structure of objects and materials and medical applications

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8
Q

uses of gamma rays

A

sterilising food and medical equipment

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9
Q

dangers of microwaves

A

internal heating of body tissue

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10
Q

dangers of infrared waves

A

skin burns

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11
Q

dangers of ultraviolet waves

A

damage to surface cells and blindness

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12
Q

dangers of gamma rays

A

cancer, mutations

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13
Q

what are waves

A

waves are a disturbance in a medium which transfers energy and information

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14
Q

what are transverse waves

A

waves in which the particles vibrate perpendicular to wave movement

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15
Q

transverse wave examples

A

light waves, water waves, S-waves, EM waves

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16
Q

what are longitudinal waves

A

waves in which the particles vibrate parallel to wave movement

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17
Q

longitudinal wave examples

A

sound waves, P-waves

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18
Q

what is the time period in waves

A

time taken for one complete wave/cycle

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19
Q

what is frequency in waves

A

the complete number of waves per second

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20
Q

how do you measure the speed of sound with microphones

A
  1. use speed = distance/time
  2. measure the distance between the two microphones using a tape measure
  3. distance must be more than 1 metre
  4. measure the time it takes for sound to travel from microphone A to microphone B
  5. repeat and take average
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21
Q

how do you measure the speed of sound using ears

A
  1. use speed = distance/time
  2. measure the distance between the two people using a trundle wheel
  3. distance must be more than 100m
  4. measure the time taken from when student sees the clap to when they hear it using a stop watch
  5. repeat and take average
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22
Q

optical fibres:

A
  • outer cladding has lower refractive index than inner core
  • light is transmitted down optical fibres by total internal reflection
  • optical fibres can bend to carry light to hard to reach places
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23
Q

doctors use endoscopes to look inside the body of a patient. explain how optical fibres are used in endoscopes.

A
  • optical fibres bend
  • some fibres carry light to the inside of the patient
  • some fibres transmit the reflected light
  • light passes up/down fibres by total internal reflection
  • light is reflected inside the patient
  • image is analysed by computer
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24
Q

how is light reflected in right-angled prisms

A

light is totally internally reflected
-> the image appears as a refection at 90 degrees to and below the object

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25
Q

what happens when a ray goes from dense to less dense?

A

it reflects away from the normal

26
Q

what does it mean when the ray refracts at 90 degrees to the normal

A

angle of incidence = critical angle

27
Q

what happens when the angle of incidence > critical angle

A

the ray undergoes total internal reflection.

28
Q

what is the critical angle

A
  • the angle of incidence
  • above which gives total internal reflection
29
Q

law of reflection

A

angle of incidence = angle of reflection

30
Q

snells law

A

n = sin(i)/sin(r)

31
Q

what is refractive index

A

a measure of how much a material slows down light waves, and therefore, how much they refract

32
Q

method to determine refractive index:

A
  1. shine a ray of light through the material at an angle
  2. measure the angle of incidence, from the normal, with a protractor
  3. measure the angle of refraction, from the normal, with a ruler
  4. plot a graph of sin(i) against sin(r)
  5. gradient = refractive index
33
Q

what happens when a light wave goes from something not very dense to something dense

A

the light wave slows down

34
Q

what happens if a wave has constant frequency but slows down

A

the wavelength would decrease

35
Q

what is refraction

A

a wave changing direction when it moves from one material to another
-> this happens because the wave speed changes when moving from one material to another

36
Q

perspex box practical

A
  1. place a Perspex box in the middle of a sheet of paper and draw around it
  2. remove the block
  3. find the middle of one of the longer sides of the block
  4. draw a line at 90 degrees to the side of the glass block at this point - this is the normal
  5. use a protractor to draw a line at 20 degrees to the normal
  6. replace the block
  7. use the ray box and a single slit to shine a ray of light along the line you have drawn - this is the incident ray
  8. look at the ray of light inside the block after leaving it
  9. mark 2 dots on the path of the emergent ray with a pencil
  10. remove the block switch off the power supply
  11. use the ruler to draw the emergent ray
  12. use the ruler to mark the path of the refracted ray inside the block
  13. use a protractor to measure the angle between the refracted ray and the normal - this is called angle of refraction
37
Q

what can sound waves be displayed as

A

oscilloscopes

38
Q

how to find frequency using an oscilloscope:

A
  1. connect oscilloscope to microphone
  2. adjust oscilloscope to get steady rate
  3. adjust time base to a minimum of one complete cycle on screen
  4. measure the number of squares for one complete cycle
  5. multiply the number of squares by the time base to find time period
  6. use frequency = 1/time period
39
Q

how to oscilloscopes display sound waves

A

as a trace on a screen

40
Q

what is the Doppler effect

A

describes how the frequency of waves changes when the source and observer are moving relative to each other

41
Q

what happens to the observed wavelength and observed frequency when the source is moving towards observer

A

wavelength - decreases

frequency - increases

42
Q

what happens to the effect on sound and effect on light when the source is moving towards observer

A

effect on sound - higher pitch

effect on light - more blue

43
Q

what happens to the observed wavelength and observed frequency when the source is moving away from observer

A

wavelength - increases

frequency - decreases

44
Q

what happens to the effect on light and effect on sound when the source is moving away from observer

A

effect on sound - lower pitch

effect on light - more red

45
Q

what happens to the observed wavelength and observed frequency when there is no relative motion

A

wavelength - no change

frequency - no change

46
Q

what happens to the effect on light and effect on sound when there is no relative motion

A

effect on sound - no change

effect on light - no change

47
Q

what is ultrasound

A

frequencies more that 20,000 Hz

48
Q

what is sound

A

frequencies between 20 - 20,000 Hz

49
Q

what is infrasound

A

frequencies less than 20 Hz

50
Q

what is the human hearing range

A

20 - 20,000 Hz

51
Q

are sound waves transverse or longitudinal

A

longitudinal

52
Q

how is an echo formed

A

sound waves reflecting off surfaces

53
Q

when playing a drum how is sound produced?

A
  • the drum skin vibrates
  • vibrations are passed onto particles in the air
  • vibrations are parallel to the direction of wave movement
54
Q

amplitude definition

A

the height of the wave (from rest to crest)

55
Q

wavelength definition

A

distance from one peak to the next

56
Q

period of wave definition

A

time taken for one complete wave to pass a point

57
Q

wave speed =

A

frequency x wavelength

58
Q

frequency =

A

1 / time period

59
Q

sin(c) =

A

1/n

60
Q

critical angle =

A

1/refractive index

physics (8 decks)

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