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Physics > 11 + 12 + 13— Waves > Flashcards

11 + 12 + 13— Waves Flashcards

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1
Q

Formula of waves.

A

V (speed, m/s) = f (frequency, Hz) x (wavelength, m)
OR
V = wavelength (m) divide time (s)

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2
Q

Formula for frequency

A

F (Hz) = 1/T (s)

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3
Q

Frequency

A

No. Of oscillations each point completes per second
SI: Hz

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4
Q

Transverse vs longitudinal waves

A

Transverse waves are waves that has a direction of vibration perpendicular to the direction of wire travel
Eg EM waves

Longitudinal waves have a direction of vibration parallel to the direction of waves travelled.
Eg sound waves

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5
Q

Period

A

Time taken by each point on the wave to complete 1 oscillation
SI: s

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6
Q

In phase

A

Alw hv the same direction of motion

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7
Q

Wave speed/velocity

A

Distance travelled by each point on the wave per second

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8
Q

Amplitude

A

Maximum magnitude of its displacement from its rest position
SI: m

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9
Q

Wavefront

A

Imaginary line on a wave that joins all points which have the same phase of vibration

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10
Q

Compressions

A

Regions whr the air pressure is slightly higher than surrounding pressure

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11
Q

Rarefractions

A

Regions whr air pressure is slightly lower than surrounding pressure

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12
Q

Echo

A

Reflected sound

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13
Q

Reverberation

A

Effect of prolonged sound due to merging of many echoes

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14
Q

What happens when waves travel from deep to shallow regions

A
  1. Bend towards normal
  2. Speed decreases
  3. Wavelength decreases
  4. Frequency unchanged
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15
Q

Characteristics of sound waves

A
  • Transmitted as longitudinal waves that consists of a series of compressions n rarefractions.
  • Cannot propagate in a vacuum as it requires a material medium to travel.
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16
Q

Wavelength

A

Shortest distance betw 2 successive troughs/crests

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17
Q

Trough

A

Lowest point of a transverse wave

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18
Q

Crest

A

Highest point of a transverse wave

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19
Q

What affects echoes produced

A
  1. Distance (long enuf)
  2. Area (large enuf)
  3. Frequency (high enuf)
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20
Q

What does frequency affect

A

Pitch. ^f ^pitch

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21
Q

What does amplitude affect

A

^amplitude, louder the sound

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22
Q

Factors that affect echoes

A
  1. Distance (long)
  2. Area (large)
  3. Frequency (high)
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23
Q

Characteristics of speed of waves

A
  1. Travels fastest in solids, slowest in gases
  2. Depends on tempt. Tempt ^, faster
  3. Depends on humidity. Tempt ^, faster
24
Q

Characteristics of electromagnetic waves.

A
  1. All em waves r transverse waves
  2. All em waves can travel without a medium, with the same spd of 3 x 10^8 m/s in a vacuum.
  3. Wave spd equation, v=f x (wavelength), applies to all em waves
  4. Em waves transfer energy
  5. Undergo reflections n rarefractions
25
Q

Frequency of sound waves from low to high.

A

Radio waves
Microwave
Infrared
Visible light
Ultraviolet
X-ray
Gamma rays

26
Q

Uses of sound waves

A

R: radio & tv communication, RFID tags, RADAR (radio detection & imaging)

M: mobile phones, microwave oven, satellite TV

I: intruder alarms, infrared remote controllers, thermal imaging

V: optical fibres in medicine & telecommunicatios, photography

U: sun beds, disinfecting water, bank note authentication

X: security screening, medical radiology, industrial defect detection in metals

G: cancer treatment, sterilising food

27
Q

Uses of echoes

A

Bats using echoes to move about
Sonar used by ships to determine depth of sea-bed

28
Q

Sound and medium

A
  • requires a material medium to travel, cannot travel in vacuum
  • Bell jar experiment -> air pumped out, sound fainter n eventually cannot be heard
29
Q

Formula to measure spd of sound

A

V = 2d/t

30
Q

Audible frequencies

A

20Hz to 20 000Hz for human ear

31
Q

Sounds w frequencies above 20 000Hz?
Sounds w frequencies below 20 Hz?

A

Ultrasound
Infrasound

32
Q

What is meant by a frequency of 5.1kHz?

A

Air molecules vibrate to-and-fro, making 5100 complete vibration per second

33
Q

Figure of sound wave with 2x frequency vs sound wave with x frequency.

A

Distance betw a compression and its neighbouring rarefractions decrease by 2 times.

34
Q

Describe distance betw adjacent particles as wave travels thru the medium

A

Distance betw adjacent particles periodically increase to a fixed max distance n then decrease to a fixed min distance

35
Q

Explain why 2 sounds r heard when experimenter bangs a pipe.

A

One sound is due to sound travelling thru metal pipe & the other thru air. Spd of sound thru pipe is greater than spd of sound thru air.

Different pipe w higher frequency: spd no change since spd of sound is not affected by frequency of sound.

36
Q

Ultrasound

A

Sound of high frequency above the range of human hearing

37
Q

Reflection of sound

A

Sound is reflected if it is blocked by a hard surface.
Most of incident sound energy is absorbed, v little is reflected if surface is soft.

38
Q

Explain how vibrations of tuning fork produce sound waves in air

A

Tuning fork vibrates and disturbs air molecules around it, causing them to vibrate to and fro about their equilibrium position. Disturbance of air molecules then passed on from molecule to molecule by collision, transmitting sound from tuning fork to microphone.

39
Q

State and explain how the wavelength of the ultrasound wave in air compares with its wavelength in oil.

A

Wavelength decreases since ultrasound waves travel slower in gases than in liquids. Since frequency remains unchanged, by v = f x wavelength, wavelength decreases.

40
Q

Briefly describe how ultrasound r used to obtain images of baby in womb.

A

Pulses of ultrasound r sent thru skin n soft body tissue of mother. When it encounters bone n cartilage tissue of the baby which is much denser, the difference in density causes ultrasound to undergo reflection. Source receives reflected ultrasound, time taken for reflected ultrasound to return is calculated n img is produced showing the depth of the baby.

41
Q

Why X-rays r not used to obtain a pic of an unborn baby

A

X-rays r high frequency high energy electromagnetic waves that can cause dmg to cells n kill cells, harming the baby.

42
Q

How sound energy is transferred without transferring matter

A

Air molecules collide w one another, transferring ke from one molecule to another

43
Q

Why sound travels faster in solids than in gas

A

Sounds travel thru the passing of vibrations in a medium. When the molecules r closely packed tgt, transfer of vibrations betw molecules more efficient -> molecules in solids closely packed vs in gas far apart -> have a higher density -> sound travels faster in solids.

44
Q

X-rays r a type of electromagnetic radiation used to produce images of the inside of the human body. State 3 possible effects on the living cells in the human body when X-rays r absorbed by body tissue.

A
  1. Death of cells
  2. Mutated cells
  3. X-rays interact w water molecules in human body to produce radicals and ions such asOH-, which can attack the cells and damage them or form toxic substances like H2O2.
45
Q

If frequency of dipping motion increases, state 2 changes to circular water wavefronts observed. [2]

A

More circular wavefronts are seen
Distance between each wavefront decreases.

46
Q

Volume of water in tray is reduced to half, frequency of dipper readjusted to original value. State 2 changes to the circular wavefronts observed. [2] (deeper to shallower water)

A

(Wavelength becomes shorter in shallower water)
More circular wavefronts are seen
Distance between each wavefront is narrower.

47
Q

As water wavefront travel outwards, they become “fainter” and less observable. Explain why. [2]

A

Wave energy dissipates to thermal energy.
Amplitude of wave decreases until it becomes non-observable.

48
Q

In terms of amplitude, wavelength and frequency, compared and comment on similarities and differences of the waves at the deep and shallow ends of the pool. [3]

A

F: same
A: shallow < deep (wave energy dissipates to internal energy as it reaches shallow)
W: shallow < deep (wave speed at shallow is slower than wave speed at deeper end)

49
Q

In terms of amplitude, wavelength and frequency, compared and comment on similarities and differences of the waves at the deep and shallow ends of the pool. [3]

A

F: same
A: shallow < deep (wave energy dissipates to internal energy as it reaches shallow)
W: shallow < deep (wave speed at shallow is slower than wave speed at deeper end)

50
Q

Explain change in direction of wave motion when depth of pool changes [2]

A

When waves enter from deeper to shallow end, refraction of water waves occurs and wave speed decreases, thus waves bend towards normal at shallow ends. Hence, change in direction of waves occurs.

51
Q

A leaf falls into the pond. Explain and state whether the leaf will move or otherwise. [2]

A

Leaf will stay at it’s original position or d metre away from edge of pond.
However, it will move up and down at its location following the perpendicular motion of transverse waves.

52
Q

Other than spacing between particles, state 3 factors that affect speed of sound and 2 factors that do not. [2]

A

Dependent:
Wind, temperature and humidity of air
Independent:
Loudness and frequency of sound

53
Q

State and explain whether speed of sound in warm air compares with speed of sound in cold air [2]

A

Sound travels slower in cold air than in warm air. [1]
The air particles in cold air travel slower and therefore take a longer time to collide with one another, resulting in sound travelling slower.

54
Q

State and explain whether speed of sound in warm air compares with speed of sound in cold air [2]

A

Sound travels slower in cold air than in warm air. [1]
The air particles in cold air travel slower and therefore take a longer time to collide with one another, resulting in sound travelling slower.

55
Q

Describe differences betw the compression and rarefractions regions in terms of air density and pressure. [2]

A

Higher air density and air pressure in compression region than rarefractions region.

Physics (18 decks)

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