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physics > waves - topic 3 > Flashcards

waves - topic 3 Flashcards

1
Q

what is a wave

A

an oscillation that transfers energy and information without transferring any matter

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2
Q

what is an oscillation

A

a vibration

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3
Q

name the 2 types of waves

A

transverse

longitudinal

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4
Q

what are transverse waves

A

waves which oscillate at right angles to the direction they travel in and transfer energy and information in

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5
Q

name 3 examples of transverse waves

A

light and the other EM waves
ripples on water
waves on springs/ strings

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6
Q

what are longitudinal waves

A

oscillation that are parallel to the direction of travel of the wave and have areas of rarefaction and compression

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7
Q

name 3 types of longitudinal waves

A

sound waves
a spring when you push on the end
P waves

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8
Q

what do waves transfer

A

energy and information but NOT MATTER

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9
Q

examples of wave transfer

A

ripples on water surface cause floating objects to bob up and down. They don’t move the object across the water to the edge. This is proof the wave travels, not the water

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10
Q

what is a crest

A

highest point of a wave

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11
Q

what is trough

A

lowest point in a wave

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12
Q

what is amplitude

A

displacement from undisturbed position to a crest or trough

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13
Q

what is wavelength

A

distance between the same point on two adjacent waves

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14
Q

what is frequency

A

number of complete waves passing a certain point per second

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15
Q

what is the period of a wave

A

the amount of time it takes for a full cycle of the wave to be complete

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16
Q

equation for period of a wave

A

1/ frequency

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17
Q

what is a period measured in

A

seconds

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18
Q

what is frequency measured in

A

Hz

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19
Q

what is distance measured in

A

M

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20
Q

what is wave speed measured in

A

M/s

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21
Q

what is the equation for wavespeed

A

distance/ time

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22
Q

how to find distance between wave source and reflective surface

A

find total distance travelled by the wave and divide by 2

23
Q

equation for wavelength

A

wavespeed/ frequency

24
Q

how to measure speed of sound in the air

A
  1. set up equipment with both microphones next to the speaker
  2. slowly move one microphone away from the speaker
  3. keep it moving until 2 traces on the oscilloscope are aligned once more
  4. measure wavelength
  5. use formula wavespeed = frequency x wavelength to find speed
  6. speed of sound is 340m/s so check your results against this
25
Q

how to measure speed of water ripples

A
  1. set up ripple tank with about 5 cm of water
  2. adjust height of wooden rod so that is just touches the surface of the water
  3. switch on the lamp and motor and adjust until low frequency waves can be clearly observed
  4. measure length of a number of waves then divide by number of waves to find wavelength
  5. count the number of waves passing a point in 10s then divide by 10 to find frequency
  6. calculate speed using v = f x y
26
Q

how to measure waves in a solid

A
  1. using the first finger and thumb on the one hand, hold a metal rod at its middle point
  2. hit one end of the rod with a hammer

3, hold a smartphone with an app which measures frequency, near the end of the rod

  1. record the peak frequency
  2. measure and record the length of the metal rod
  3. calculate the speed of the waves using the frequency and wavelength
27
Q

what 3 things can happen when a wave arrives at a boundary

A

absorption by 2nd material which transfers energy to material

reflection - waves may bounce back from 2nd material

transmission - waves may carry on travelling however they often undergo refraction

28
Q

when does refraction occur

A

Refraction occurs when light changes direction as it passes from one medium to another due to the change in its speed.

29
Q

what happens to the angle of refraction if a refracted ray bends towards the normal

A

angle of refraction will be smaller than angle of incidence

30
Q

how to investigate refraction

A

place glass block one a piece of paper and trace around

use ray box to shine a ray of light at the middle of one side of the box

trace the incident ray on the paper and do the same for the light ray

remove the block and join up both rays to find the path of the refracted ray

draw the normal at the point where light entered the block

use a protractor to measure angle of incidence and refraction

repeat 3 times, keeping angle of incidence the same and calculate and average for each angle

31
Q

what happens if a wave slows down at a boundary

A

it bends towards the normal

32
Q

what happens if a wave speeds up at a boundary

A

it bends away from the normal

33
Q

what are sound waves

A

sound waves are longitudinal waves of vibrating particles caused by vibrating objects

34
Q

what happens to sound waves as they enter different materials

A

they will refract

35
Q

what happens when a sound wave meets a solid object

A

air particles hitting the object causes the closest particles in the solid to vibrate and this continues. This series of vibrations passes sound waves through the object

36
Q

how do we hear things

A

sound waves of certain frequencies that reach your ear drum cause it to vibrate

vibrations passed on to tiny bones in the ear through the semicircular canals and to the cochlea

the cochlea turns vibrations into electrical signals, sent to the brain

this allows you to hear sounds

37
Q

what frequencies can humans hear between

A

20 Hz to 20,000 Hz

38
Q

why is there a limit to the frequency we can hear between

A

due to the size and shape of our ear drums

39
Q

what is ultrasound

A

sound wavs with frequencies greater than 20,000 Hz and so it can’t be heard by people

40
Q

what can ultrasound be used for

A

foetal scanning, sonar ( which is used in the military or commercial fishing

41
Q

how is ultrasound used in foetal scanning

A

to produce an image of an unborn baby so we can identify any problems with the baby’s development early

42
Q

what is active sonar

A

a type of sonar used by boats and submarines where high frequency sound waves are used to find out the depth of water or to locate objects

43
Q

how active sonar is used to find out the depth of objects or locate objects

A

a pulse of sound waves is emitted by submarine and the time taken for the echo to return is measured. Then if you know the speed of sound in water you can find depth using distance = wavespeed x time

44
Q

infrasound

A

sound waves with frequency below 20 Hz

45
Q

what is infrasound used for

A

detecting distant volcanic eruptions or in exploring structures and properties of the Earth’s core

46
Q

how ultrasound waves are used to detect fishes

A

ultrasound waves go down through the water. ultrasound waves are reflected off fish. reflected ultrasound waves are received by boat. time delay shows how
deep fish are

47
Q

what are wavefronts

A

imaginary lines drawn through identical points on waves

48
Q

what is wave speed

A

how fast a wave moves, or how fast it transfers energy or information

49
Q

what is wave velocity

A

the speed of a wave in a certain direction

50
Q

what are the 2 types of seismic waves

A

p waves and s waves

51
Q

what are p waves

A

longitudinal waves which can travel through both solids and liquids and travel faster in solids

52
Q

what are s waves

A

transverse waves which can only pass through solids

53
Q

how are seismic waves used to explore the earth’s structure and core

A

by measuring the seismic waves detected at various points on Earth , seismologists can build up a picture of the paths the waves have travelled along from the point of origin to points of detection . This allows them to work out any boundaries between different materials within Earth.

54
Q

what do seisometers do

A

seismic waves from an earthquake can be detected at different points on the surface of the planet using seisometers

physics (14 decks)

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