Waves Flashcards

1
Q

what is the amplitude of a wave?

A

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

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2
Q

what is the frequency of a wave?

A

the number of complete waves that pass a point per second

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3
Q

what is the period of a wave?

A

amount of time taken for a full cycle of the wave to pass a point

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4
Q

what is wave speed?

A

speed at which energy is being transferred by the wave

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5
Q

what 3 things can happen at a boundary between 2 different materials?

A
  1. absorbed, which transfers energy to the material’s energy stores
  2. transmitted - often causes refraction
  3. reflected
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6
Q

what is specular reflection?

A

when a wave is reflected in a single direction by a smooth surface
it forms a clear image

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7
Q

what is diffuse reflection & why does it occur?

A

when a wave is reflected by a rough surface & reflected waves are scattered in several directions
normal is different for each incident ray so angle of incidence is different for each ray so angle of reflection different

the surface appears matte
image is blury

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8
Q

how does density affect wave speed?

A

the greater the density, the lower the wave speed

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9
Q

what is optical density?

A

how quickly light can pass through an object
the higher the optical density, the slower light waves can travel through it

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10
Q

what do em waves transfer energy from & to?

A

from a source
to an absorber

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11
Q

how are radio waves produced & how do they transfer data?

A
  1. an alternating current has oscillating charges, which produce oscillating magnetic fields
  2. this produces electromagnetic waves/radio waves
  3. the frequency of waves = frequency of alternating current
  4. energy is transferred from waves to the electrons in the material of the receiver, causing the electrons to oscillate at the same frequency as the waves
  5. if circuit is complete, this generates alternating current in the receiver (same frequency as radio wave)
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12
Q

what are the uses of radio waves & why are they suitable?

A

long-distance communication
radio waves with longer wavelengths diffract/bend around the curved surface of Earth
radio waves with shorter wavelengths reflect off the ionosphere

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13
Q

what are the uses of microwaves & why are they suitable?

A

satellite communication
can easily pass through Earth’s watery atmosphere

cooking food
absorbed & transfer energy to water molecules in food

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14
Q

what are the uses of visible light waves & why are they suitable?

A

optical fibres
visible light is not easily absorbed or scattered by fibres

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15
Q

what is radiation does a measure of?

A

risk of harm from the body being exposed to radiation
not
total amount of radiation absorbed

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16
Q

what does the risk of radiation depend on?

A

total amount of radiation absorbed & type of radiation

17
Q

what is the principal focus for a convex lens?

A

the point where rays of light parallel to the axis meet

18
Q

what is the principal focus for a concave lens?

A

the point behind the lens where rays hitting lens parallel to axis seem to come from

19
Q

what are the 3 rules for refraction in a convex lens?

A
  1. an incident ray parallel to axis refracts through lens & passes through principal focus on the other side
  2. an incident ray passing through the principal focus refracts through the lens & travels parallel to the axis
  3. an incident ray passing through the centre of the lens continues in same direction
20
Q

what are the 3 rules of refraction in a concave lens?

A
  1. an incident ray parallel to the axis refracts through lens & travels in line with principal focus (appears to have come from the principal focus)
  2. incident ray passing through the lens towards principal focus refracts through lens & travels parallel to axis
  3. incident ray through the centre continues in same direction
21
Q

how does the distance from the lens affect the image produced?

A

convex lenses:
an object at 2f produces a real, inverted image the same size as the object at 2f

an object between f & 2f produces a real, inverted image larger than the object beyond 2f

an object nearer than f produces a virtual, upright image larger than the object on the same side

22
Q

what does the colour of an object depend on?

A

which wavelength of visible light is reflected most strongly

23
Q

what do non-primary-coloured objects reflect?

A

the wavelengths of that colour
or
the wavelengths of the primary colours that mix together to make that colour

24
Q

how do filters for non-primary colours work?

A

they transmit the wavelengths of light for that colour & the wavelengths of the primary colours that can be added together to make that colour

25
what is a perfect black body?
an object that absorbs all incoming radiation so it does not reflect or transmit any radiation best possible emitters
26
why do all objects emit em radiation?
due to energy in their thermal stores
27
what 2 things about the wavelengths emitted by an object depend on its temperature?
intensity & distribution
28
what is intensity?
power per unit area
29
what is the relationship between temperature & intensity of every wavelength emitted?
the greater the temperature, the greater the intensity of every wavelength emitted
30
how does the speed of an increase in intensity differ across wavelengths & how does this affect the peak wavelength?
the intensity of waves increases faster for shorter wavelengths the peak wavelength decreases
31
what happens to the earth’s temperature in the day & at night?
in the day: increase in temperature bc lots of radiation is absorbed & transferred from Sun to Earth at night: decrease in temperature bc less radiation is being absorbed than emitted/radiation is absorbed at a faster rate than it is emitted
32
why can sound not travel through space?
it is a vacuum so there are no particles to move or vibrate to transfer sound
33
how do humans hear sound?
ear drum vibrates tiny bones in the ear vibrate the cochlea turns vibrations into electrical signals that are transmitted along the auditory nerve to the brain, which interprets signals
34
what is the range of human hearing limited by?
the size & shape of the eardrum the structure of parts of the ear age the maximum frequency the eardrum can vibrate at
35
describe the refraction of sound waves?
when sound waves enter a denser material they speed up
36
how is ultrasound produced?
electrical devices produce electrical oscillations then turn mechanical vibrations into sound waves
37
what are the uses of ultrasound & explain?
medical imaging e.g. foetuses at boundary between 2 different materials, some waves are reflected & detected, which shows the shape the timing & distribution of echoes are measured to produce a video image industrial uses e.g. to detect cracks in pipes waves are usually reflected by the far side of the material if there is a crack, waves will be reflected sooner than expected & detected
38
what happens to seismic waves at boundaries inside earth?
some waves are refracted & some are absorbed
39
what can be worked out from observing seismic waves?
the internal structure of earth & where the layers are bc properties of earth change significantly density of layers