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Physics > Topic 4: Waves > Flashcards

Topic 4: Waves Flashcards

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1
Q

What does frequency mean?

A

The number of waves passing a point each second. (Measured in hertz (Hz) )

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2
Q

What does period mean?

A

This is the length of time it takes one wave to pass a given point. Measured in seconds (s)

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3
Q

What does wavelength mean?

A

This is the distance from a point on one wave to pass a given point. Measures in meters (m)

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4
Q

What does amplitude mean?

A

This is the maximum distance from a point on the wave away from it rest position. Measures in meters.
(The greater the amplitude the louder the sounds.)

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5
Q

What does velocity mean?

In terms of waves

A

The speed and direction a wave is traveling.

Waves travel at different speeds in different materials.

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6
Q

What are transverse waves?

A

Waves that particles move up and down at right angles to the direction the wave is travelling. They have side ways vibrations.
Can travel through empty space don’t transfer matter.

Examples: electromagnetic waves, S waves, water waves.

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7
Q

What are longitudinal waves?

A

The vibrations are parallel to the direction the wave travels. Longitudinal waves squash and stretch out the arrangement of the particles in the material they pass through.
They need matter to travel through.

Examples: sound waves, P waves

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8
Q

Equations for wave speed…

A

Wave speed = Frequency x wavelength

Or

Speed = distance /time

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9
Q

How do we hear sound?

A

1- sound waves enter the ear canal
2- the ear drum is a thin membrane, sound waves make it vibrate.
3- vibrations are passed on to tiny bones which amplify the vibrations.
4- vibrations are passed on to the liquid inside the cochlea.
5- Tiny hairs inside the cochlea detect vibrations and create impulses - electrical signals.
6- Impulses travel along neurones in the auditor nerve to reach the brain.

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10
Q

What is the cochlea?

A

The cochlea is a coiled tube containing liquids. Each hair cell is connected to a neurone that send impulses to the brain. Brain interprets these signals from different neurones as different pitches of sound.

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11
Q

What is the hearing range of a human?

A

20Hz - 20 000Hz (20 000Hz = 20KHz)

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12
Q

What is ultra sound?

A

Sounds with a frequency higher 20 000 Hz are called ultrasound

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13
Q

What is infra sound?

A

Sounds with a frequency less than 20 hz are too low for humans to hear.

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14
Q

How is ultrasound used?

A

Some animals such as wales, dolphins and bats use it by sending out waves and the waves are then reflected by nearby objects and the animals listen for echoes.

Sonar equipment can be carried on ships and submarines to detects fish and find out the depth of the sea. It can also map the sea bed.

Can be used to see unborn babies and see how they develop

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15
Q

What do ultrasound scans do?

A

The make images of things inside the body. They pass through tissue rather than absorb it and that’s why it is used as a scanner.

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16
Q

What do waves do?

A

They transfer energy and information not matter.

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17
Q

How do u work out the distance of an earthquake?

A

Distance = 8.65 x time difference (seconds).

Time difference = arrival of p wave - arrival of S wave

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18
Q

Describe a light ray going through a glass block…

A

Light bends toward the normal when it goes through a medium where it travels more slowly. It bends away from the normal when it goes through a medium when it travels faster

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19
Q

How does an ultra sound scanner work?

A

1: a gel is used to stop ultrasound reflecting from the skin.
2: Some sound is reflected when ultrasound waves pass through different materials such as- fat, muscle, bone.
3: the probe emits and receives ultrasound waves.
4: the machine detects the time between sending pile out and echo. The display shows where echo comes from.
5: the further down the screen the longer the echo took to get back to screen.

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20
Q

What does a seismometer do?

A

Detect the activity of seismic waves.

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21
Q

What are seismic waves?

A

The vibrations caused by earthquakes are called seismic waves. The waves travel as P waves and S waves.

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22
Q

What are the properties of P waves?

A
  • P waves are longitudinal waves.
  • P waves are faster than S waves and arrive first.
  • P waves travel through solids and liquids.
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23
Q

What are the properties of S waves?

A
  • S waves are transverse waves.
  • S waves are both slower and weaker than P waves.
  • S waves ONLY travel through solids so they cannot travel through liquids including the outer core.
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24
Q

What are shadow zones?

A

The places where waves are detected depend where the earthquakes occur but there is always a large area of the earth on the opposite side where no waves are detected.

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25
Q

How do seismic waves follow curved paths through the earth?

A

This is because they are reflected or refracted as they pass from one rock to another. Properties of rock change with increasing depth and this changes the speed of the seismic wave. This makes them curve refract if there is a sudden change in rock and will not be reflected back.

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26
Q

What does the speed of a wave depend on?

A

The medium it is travelling through.

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26
Q

What is the speed of light and what could slow it down?

A

The speed of light is 3,000,000 m/s in a vacuum but it travels more slowly in glass or water. When light goes from air into water it’s wavelength also reduces.

27
Q

How can you find the speed of sound? Give an example:

A

By measuring the time it takes for a sound to travel a certain distance.
E.g. if you stand in front of a large wall you can measure the time it takes for the echo of the sound to reach you.
Speed = distance / time

28
Q

How can you measure the speed of water waves?

A

Time it takes for the wave to travel between two fixed points. Speed can be calculated form the distance and time.

29
Q

When does refraction occur?

A

This happens at the interface (boundary) between two media.

30
Q

What is refraction?

A

the change in direction of a wave.

31
Q

What is the normal?

A

A line at right angles to the interface.

32
Q

When does light travelling through a different medium not change direction?

A

When it travels through the normal.

33
Q

Give a real life example of refraction and why it occurs:

A

An object at the bottom of the swimming pool may look closer than it actually is

34
Q

Give 2 example of transverse waves:

A
  • electromagnetic waves

- S waves

34
Q

Give 2 examples of longitudinal waves:

A
  • P waves
35
Q

How can frequency or amplitude be used to communicate?

A

A change in frequency, wavelength or amplitude can be used to transfer information form one place to another.

36
Q

How can waves change speed and direction?

A

When they move into a different medium.

37
Q

When does light not change direction when going through a different medium?

A

When it travels along the normal it does not change speed.

38
Q

How do we see objects?

A

When light is reflects form them and enters our eyes.

39
Q

Why does an object at the bottom of a swimming pool look closer than it actually is?

A

Light reflected by it changes direction when it leaves the water.

40
Q

How do wave speeds differ through different medium?

A

Waves can travel through different media at different speeds. E.g light travel faster in air than it does water or glass. As light passes the interface between one medium and another it changes speed. This speed can cause the direction of light to change.

41
Q

What does the bend when light enters a different medium depend on?

A

Depends on how fast the light travels in the two media and the angle of the light hitting the interface. THE GREATER THE DIFFERENCE IN SPEED BETWEEN THE TWO MEDIA THE GREATER THE BEND.

42
Q

When does light bend towards the normal?

A

When it slows down and it bends away when it speed up.

43
Q

Explain the water wave model.

A

The speed of water on waves depend on how deep the water is. Waves moving from deep to shallow water slow down and change direction

44
Q

When a wave reaches a boundary what happens?

A

They can be:
Reflects-bounces of boundary
Refracted- wave passes into new material but changes direction and speed it’s travelling.
Transmitted-wave passes into new material and is not absorbed or reflected.
Absorbed-wave disappears as the energy it was carrying is transferred to the material.

45
Q

Which colours reflects better and which absorb better?

A

Lighter colours/objects reflect more light (that’s why snow is cold, because it reflects heat) and darker objects absorb light more.

46
Q

What is white light?

A

This comes form the sun or lightbulbs and is made up of a number of different frequencies of light. We see these different frequencies as different colours.

47
Q

Why is a prism used to split up white (visible) light?

A

They change speed at different amounts when they travel through different mediums (e.g air to glass). This means they are refracted through varying angles, which is why a prism is used to split up visible light into colour of the rainbow.

48
Q

How are sound waves similar to light and can they be refracted?

A

THEY CAN BE AFFECTED IN THE SAME WAY AS LIGHT WAVES. (Reflected, refracted, absorbed and transmitted) We hear echoes when sound is reflected by a hard surface. Sound is also refracted when it goes through different mediums but it is harder to observe.

49
Q

If the speed of a wave changes what else also changed?

A

Wave velocity is equal to frequency multiplied by wave length. So if the velocity changes with the frequency or wavelength (or both) must change.

50
Q

When we hear a sound at different pitches what are our ears detecting?

A

Our ears detect the different frequencies of a sound (not the wavelength).

51
Q

Does the pitch of a sound change when it travels through air or solid?

A

It has the same pitch weather it reaches us through air or a solid so when a sound wave enters a different material it is the wavelength and velocity that change not the frequency.

52
Q

How does a sound wave travel?

A

Sound waves are longitudinal waves. Particles in a liquid or gas vibrate backwards and forwards when a sound wave passes. When the sound wave reaches a solid some of the energy it is transferring is reflected, absorbed and transmitted.

53
Q

How does a sound wave cause changes in pressure on a solids surface?

A

This causes particles in the solid to vibrate and so the disturbance is passed from air to solid. Vibration in a solid can be passed as both longitudinal and transverse waves.

54
Q

How do sound waves travel through our ears?

A

1) sound waves enter the ear canal
2) the eardrum is a thin membrane. Sound waves make it vibrate.
3) vibrations are passed onto tiny bones which amplify the sound the vibrations.
4) vibrations are passed onto the liquid inside the cochlea.
5) tiny hairs inside the cochlea detect these vibrations and create electrical signals called impulses.
6) impulses travel along neurones in the auditory nerve to reach the brain and interpret the sound.

55
Q

What is the hearing range for humans?

A

20Hz-20,000Hz

56
Q

What is the structure of the cochlea?

A

The middle of the tube is thicker and stiffer at the base and and thinner at the apex. The part of the membrane that vibrates depends on the frequency of the sound waves in the liquid inside the cochlea.

57
Q

How do animals use ultrasound?

A

The ultrasound waves they make are reflected from things around them. They listen back to the echo.

58
Q

How does sonar equipment work and why is it used?

A

It is used to find the depth of sea and used to detect fish. A speaker on the ship emits a pulse of ultrasound. This spreads out through the water and is reflected by sea bed. A microphone detects the echo and calculates the time difference that it took for impulse to be sent and detected. The equation distance = speed x time is used to work out the distance.

59
Q

What is the speed of sound in water?

A

1500m/s

60
Q

What is the speed of sound and light through a vacuum?

A

Light: 3,000,000 m/s

Sound: 330 m/s

61
Q

What produces infra sound waves?

A

Volcanic eruptions and earthquakes.

62
Q

What type of waves to Earthquakes release?

A

P waves and then S waves.

63
Q

What is the difference between longitudinal and transverse waves?

A

Longitudinal waves can be transmitted through solids, liquids and gases. However transverse waves need a medium to travel through so can therefore only be transmitted through solids.

64
Q

How do scientists create the interior model of the Earth?

A

Through the path of S waves and P waves. They use information about the time the wave arrives and the speed the the wave travels through in different rock types.

Physics (11 decks)

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