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Physics > Topic 6 - Waves > Flashcards

Topic 6 - Waves Flashcards

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1
Q

How do waves transfer energy?

A

They oscillate and transfer energy from one place to another, but do not transfer matter.

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2
Q

What is the amplitude of a wave?

A

The maximum displacement of a point on a wave from its undisputed position ( like the highs on a sine wa).

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3
Q

What is the frequency of a wave?

A

It is the number of complete waves per second in Hz.

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4
Q

What is the wavelength?

A

The distance between the same two points (eg the trough) on a wave.

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5
Q

Give the equation for the period, or full cycle, of a wave.

A

T = 1/f
T is time in s
F is frequency in Hz

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6
Q

What is a transverse wave? Give an example of a transverse wave.

A

A transverse wave has oscillations perpendicular to the direction of energy transfer. It looks like a sine wave. An example is an electromagnetic wave, but most waves are transverse.

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7
Q

What is a longitudinal wave? Give an example.

A

A longitudinal wave has oscillations parallel to the direction of energy transfer. An example is a sound wave.

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8
Q

Give the equation for wave speed.

A

V = fλ
V is wave speed in m/s
F is frequency in Hz
ο is wavelength in m

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9
Q

What 3 things can happen when a wave reaches a boundary between two different materials?

A

Absorption, which transfers energy into the material’s energy stores.
Transmission, where the wave travels through the material and often causes refraction.
Reflection.

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10
Q

What is the angle of incidence and what is it equal to?

A

It is the angle between the incoming wave and the normal. It is equal to the angle of reflection.

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11
Q

What is the normal and what is it shown as on a ray diagram?

A

It is a line perpendicular to the boundary. It is shown with a dotted line.

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12
Q

When does specular reflection occur?

A

When a wave is reflected at a single angle on a smooth surface, like a mirror.

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13
Q

When does diffuse reflection occur?

A

When waves are reflected off a rough surface in multiple directions.

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14
Q

Why does diffuse reflection occur?

A

Because of the rough texture, each wave will have a different normal and so will be reflected in different directions because the angle of incidence will be different for each one. When light is reflected on a rough surface, the reflection is matte, not shiny.

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15
Q

Give 3 properties of EM waves.

A

EM waves are transverse.
EM waves travel at the same speed through air and a vacuum like space.
EM waves form a spectrum over different wavelengths.

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16
Q

What are the 7 groups of wavelengths in EM waves?

A

1) Radio - 1m to 10(to the power of)4m
2) Micro - 10(to the power of)-2m
3) Infrared - 10(ttpo)-5
4) Visible - 10(ttpo)-7
5) UV - 10(ttpo)-8
6) X Ray - 10(ttpo)-10
7) Gamma - 10(ttpo)15

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17
Q

What does the amount that a wave is refracted rely on?

A

The speed of the wave, which depends on the density of the material it is passing through. If it is denser, the wave slows and bends towards the normal. If it is less dense, the opposite happens. THE WAVELENGTH CHANGES BUT THE FREQUENCY DOES NOT.

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18
Q

What is optical density?

A

How fast light can travel through an object. If the optical density is higher, the wave is slower.

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19
Q

How are radio waves produced?

A

Oscillating waves are made using oscillating magnetic and electric fields from AC currents. The frequency of the current is equal to the frequency of the wave. The device used to created these waves is a transmitter.

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20
Q

How do radio waves pass between devices?

A

The wave is transmitted and reaches a receiver, where the wave is absorbed. The energy the wave carries is also absorbed and and transferred to the material in the receiver. This makes the receiver oscillate and generates an ac with the same frequency as the wave if it is part of a complete circuit.

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21
Q

What is the frequency of long-wave radio waves and what are their uses?

A

The frequency is 1 - 10km and can travel halfway around the world because they can bend around the planet’s curvature and diffract off hills and through tunnels, meaning they can be transferred to receivers even if they aren’t in the wave’s line of sight.

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22
Q

What is the frequency of a short - wave radio waves and what is it used for?

A

10m - 100m. They can be used at long distances because they reflect off the ionosphere. Bluetooth is an example.

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23
Q

What properties does the wave used for TV and radio have (buildings…)?

A

They have a very short frequency and have to be in line with the transmitter because they can’t bend or travel far through buildings.

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24
Q

How are microwaves used by satellites?

A

Microwaves can travel through the atmosphere, so they are sent into space and are picked up by a receiver dish in space, which reflects it in a different direction back to Earth. It’s received by a satellite dish on earth but there is a slight time delay because of the distance.

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25
Q

How are microwaves used in microwave ovens?

A

They are used at a different wavelength to satellite communications so that water molecules in the food pick them up and heat up, quickly transferring heat energy to the rest of the food.

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26
Q

How is infrared (IR) used to monitor heat?

A

Hot objects give off more IR radiation as they heat up. Infrared cameras detect this and turn it into an electrical signal, showing the heat of objects.

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27
Q

How is IR used to heat things up in food and homes?

A

In food, IR waves are absorbed and cause the food to heat up. In homes, electric heaters contain a long wire that heats up a lot, giving off a lot of IR radiation. This radiation is absorbed by objects and air.This heats up the area by transferring energy to the thermal energy store, causing a home to heat up.

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28
Q

How do fibre optic cables work?

A

They transmit information through visible light that bounces along the wire due to reflection. Not a lot of the visible light is absorbed or scattered during this.

29
Q

What is fluorescence?

A

A property where some objects can absorb UV and emit visible light.

30
Q

What emits UV?

A

The sun emits UV, which tans our skin.

31
Q

How do UV lights work?

A

They generate UV, which is converted to visible light by phosphorous inside. They are energy efficient.

32
Q

How does an X Ray work?

A

The X-Rays can travel through your flesh, but not your bone, so an image come up of your bones so that radiographers can check bone health or teeth.

33
Q

How does radiotherapy work?

A

Radiotherapy is used to kill cancerous cells by directing high levels of gamma or X rays in a concentrated area.

34
Q

How are gamma rays used in medical tracers?

A

A person swallows or is injected with a tracer that emits gamma rays and doctors detect it around the body as the waves pass through the flesh.

35
Q

How do radiographers protect themselves from X or Gamma rays?

A

They wear lead or leave a room.

36
Q

Why is UV radiation dangerous?

A

Because it can damage surface cells, causing burns, aging of the skin, or even increased risk of skin cancer.

37
Q

Why are X rays and gamma rays dangerous?

A

They are ionising, causing gene mutation or cell destruction and cancer.

38
Q

What unit is the risk of damage from radiation exposure measured in?

A

Sieverts, or Sv. Milli Sieverts are used more. 1000mSv is 1Sv.

39
Q

Is the chest more or less risky to expose to radiation than the head and why?

A

The chest because you are 4 times morelikely to suffer gene mutations in a chest CT scan than a head CT scan.

40
Q

Describe a convex lens. (Axis, principle focus etc)

A

Convex lenses bulge outwards. The axis is the dotted line through the centre of the lens. The bulge causes all of the rays of light to converge at the principle focus.

41
Q

Describe a concave lens. (Axis, principle focus etc)

A

A concave lens bends inwards. The axis is the dotted line through the centre. The principle focus is where rays hitting the lens parallel to the axis all meet, since the concave lens makes all the rays that hit is spread out rather than meet up.

42
Q

What are the 3 rules for refraction in a concave lens?

A

An incident ray parallel to the axis travels through and becomes in line with the principle focus so it looks like that’s where it came from.
An incident ray passing through the lens becomes parallel to the axis.
An incident ray passing through the centre continues in the same direction.

43
Q

What are the 3 rules of refraction in a convex lens?

A

An incident ray parallel to the axis passes through and creates a principle focus.
An incident ray passing through the principle focus refracts back to make a ray parallel to the axis.
An incident ray passing through the centre carries on in the same direction.

44
Q

What is a real image?

A

Where light forms an image on a ‘screen’, like on the retina in the eye.

45
Q

What is a virtual image?

A

Where rays diverge so the light from the object appears to be coming from somewhere completely different, such as in a mirror or magnifying glass.

46
Q

What type of image does a convex lens always create?

A

A virtual image.

47
Q

How does a magnifying glass work?

A

A concave lens is placed towards an object. This object must be closer to the lens than the focal point. This creates a virtual image of the object.

48
Q

How are certain objects different colours?

A

They only reflect certain wavelengths, which create different colours. A blue hat reflects blue light, and so on. The rest are absorbed.

49
Q

How would a red hat look under a blue colour filter and why?

A

It would look black. This is because the colour filter absorbs all other colours including red, so the red hat would be black.

50
Q

How does IR work with a cup of hot chocolate compared to a cup of cold water?

A

A cup of hot chocolate gives out more radiation than it absorbs, so it gives off more heat and slowly cools. A cup of cold water absorbs more radiation than it gives off, so it stays cool but slowly heats up.

51
Q

What is a Leslie cube?

A

A watertight cube with different textured and coloured surfaces to experiment with how IR emission happens on different surfaces.

52
Q

What is a black body?

A

The best possible emitter of wavelengths. It absorbs all radiation that hits it.

53
Q

What does radiation from an object depend on?

A

An object’s temperature. As temperature increases, distribution and intensity (power per unit area) increases but some smaller wavelengths increase faster than longer ones.

54
Q

How does radiation effect the world’s temperature?

A

During the day, radiation from the sun is absorbed, making the area warmer. At night, more radiation is emitted than absorbed, making it cooler. If the atmosphere absorbs more radiation than it emits, it makes the world warmer. This is global warming.

55
Q

What forms sound waves?

A

Vibrating objects that send longitudinal waves through a medium.

56
Q

Give 3 properties of sound waves.

A

When they travel through solids, the particles of the solid vibrate.
They pass faster through solids than liquids, and faster through liquids than gases.
Sound can’t travel through a vacuum.

57
Q

How do we hear?

A

A sound wave causes the ear drum to vibrate. This is passed to small bones called ossicles and then onto the cochlea. These signals get turned into electric signals which are sent to the brain.

58
Q

What frequencies can we hear?

A

20 Hz to 20kHz

59
Q

What are sound waves reflected by?

A

Hard, flat surfaces. This is what an echo is.

60
Q

How do sound waves refract?

A

They speed up in denser material because the wavelength changes but frequency remains the same, so speed must change.

61
Q

What frequency is ultrasound above?

A

20 000 Hz

62
Q

Does ultrasound get fully or partially reflected? What use does this have?

A

Partially reflected. It can be used for ultrasound scans for babies and industrial imaging.

63
Q

How does ultrasound baby scanning work?

A

Ultrasound is fired at a pregnant woman’s belly and some of the waves get reflected off the surface of the foetus. A computer picks up these signals and converts them into an image. No one knows if it is fully safe but it is much safer than x rays.

64
Q

What is echo sounding?

A

Where high frequency sound waves or ultrasound waves are fired and the bounce back is detected. Some boats use it to find out the depth of water or to find objects beneath the boat.

65
Q

What waves does an earthquake give off? How do we use this information?

A

A seismic wave. They can be detected on seismometers by seismologists and the distance between the seismometer and the place where the waves originated can be detected.

66
Q

What happens when seismic waves deflect off a surface?

A

If they are refracted and start to speed up gradually, then it creates a curve. If the properties change quickly they speed up quickly, creating a kink in the path.

67
Q

What are the qualities of P waves?

A

They are longitudinal.
They can travel through solids and liquids (including the earth’s core).
They are faster than S waves.

68
Q

What are the properties of S - waves?

A

They are transverse.
They can’t travel through solids or liquids (or the earth’s core).
They are slower than P-waves.

Physics (10 decks)

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