Waves

Question 1

what is the amplitude of a wave?

Answer 1

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

Question 2

what is the frequency of a wave?

Answer 2

the number of complete waves that pass a point per second

Question 3

what is the period of a wave?

Answer 3

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

Question 4

what is wave speed?

Answer 4

speed at which energy is being transferred by the wave

Question 5

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

Answer 5

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

Question 6

what is specular reflection?

Answer 6

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

Question 7

what is diffuse reflection & why does it occur?

Answer 7

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

Question 8

how does density affect wave speed?

Answer 8

the greater the density, the lower the wave speed

Question 9

what is optical density?

Answer 9

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

Question 10

what do em waves transfer energy from & to?

Answer 10

from a source
to an absorber

Question 11

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

Answer 11

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)

Question 12

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

Answer 12

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

Question 13

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

Answer 13

satellite communication
can easily pass through Earth’s watery atmosphere

cooking food
absorbed & transfer energy to water molecules in food

Question 14

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

Answer 14

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

Question 15

what is radiation does a measure of?

Answer 15

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

Question 16

what does the risk of radiation depend on?

Answer 16

total amount of radiation absorbed & type of radiation

Question 17

what is the principal focus for a convex lens?

Answer 17

the point where rays of light parallel to the axis meet

Question 18

what is the principal focus for a concave lens?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

what does the colour of an object depend on?

Answer 22

which wavelength of visible light is reflected most strongly

Question 23

what do non-primary-coloured objects reflect?

Answer 23

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

Question 24

how do filters for non-primary colours work?

Answer 24

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

Question 25

what is a perfect black body?

Answer 25

an object that absorbs all incoming radiation so it does not reflect or transmit any radiation
best possible emitters

Question 26

why do all objects emit em radiation?

Answer 26

due to energy in their thermal stores

Question 27

what 2 things about the wavelengths emitted by an object depend on its temperature?

Answer 27

intensity & distribution

Question 28

what is intensity?

Answer 28

power per unit area

Question 29

what is the relationship between temperature & intensity of every wavelength emitted?

Answer 29

the greater the temperature, the greater the intensity of every wavelength emitted

Question 30

how does the speed of an increase in intensity differ across wavelengths & how does this affect the peak wavelength?

Answer 30

the intensity of waves increases faster for shorter wavelengths
the peak wavelength decreases

Question 31

what happens to the earth’s temperature in the day & at night?

Answer 31

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

Question 32

why can sound not travel through space?

Answer 32

it is a vacuum
so there are no particles to move or vibrate to transfer sound

Question 33

how do humans hear sound?

Answer 33

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

Question 34

what is the range of human hearing limited by?

Answer 34

the size & shape of the eardrum
the structure of parts of the ear
age
the maximum frequency the eardrum can vibrate at

Question 35

describe the refraction of sound waves?

Answer 35

when sound waves enter a denser material they speed up

Question 36

how is ultrasound produced?

Answer 36

electrical devices produce electrical oscillations then turn mechanical vibrations into sound waves

Question 37

what are the uses of ultrasound & explain?

Answer 37

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

Question 38

what happens to seismic waves at boundaries inside earth?

Answer 38

some waves are refracted & some are absorbed

Question 39

what can be worked out from observing seismic waves?

Answer 39

the internal structure of earth & where the layers are
bc properties of earth change significantly
density of layers