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(A) Physics > P5 > Flashcards

P5 Flashcards

1
Q

What are waves

A

An oscillation that transfers energy

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2
Q

What are longitudinal waves

A

Waves that have oscillations parallel to energy transfer
They require a medium like air as the energy is transferred when particles collide

When the oscillations are further apart there are rarefractions
When they are close together there are compressions

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3
Q

What are transverse waves

A

Waves that move (oscillate) at 90° to the direction of energy transfer
They do not always require a medium to travel through

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4
Q

What is amplitude

A

Distance from the trough to the crest of a wave (bottom to top)
Symbol - A
Measurement - depends on the wave, e.g m or v

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5
Q

What is wavelength

A

The distance from one point of a wave to the same point on the next eave

Symbol - λ - lambda
Unit - meters

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6
Q

What is frequency (waves)

A

The number of oscillations per second
Symbol - F
Units - Hertz

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7
Q

What is the time period (waves)

A

The time taken for a wave to pass a specific point
Symbol - T
Unit - seconds

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8
Q

What is wave velocity

A

The speed at which a wave transfers energy or information

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9
Q

How do you calculate wave velocity

A

Frequency × wavelength

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10
Q

How can waves be modeled

A

Using a ripples on water to model transverse waves

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11
Q

What happens when waves enter a different medium

A

Their velocity change causing the wave to refract

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12
Q

Why does entering a denser medium cause a wave to refract

A

Entering a denser medium causes the speed of the wave to decrease
So wave to bend towards the normal
The wave length decreases and the frequency stays the same

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13
Q

What happens to sound waves at a boundary

A

They are either
Absorbed
Transmitted
Reflected

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14
Q

What is an echo

A

A refraction of sound

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15
Q

What is echo sounding

A

A process of finding the distance between two points, by using the time it takes to reflect a sound wave

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16
Q

What is sonar

A

Sound
Navigation
And
Ranging

It is used to find distances using echo-sounding

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17
Q

What is ultrasound

A

A sound frequency greater than 20,000hz
We cannot hear it but many animals can

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18
Q

Why is ultrasound usefull

A

It has a short wavelength so can easily be focused into a beam

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19
Q

How is ultrasound used

A

It can be used to make an image of a fetus

Ultrasound beams are transmitted into the mother (by the transmitter)
As there are different boundaries the waves are reflected and absorbed
The machine calculates the distance of each point using time and velocity, and those points are used to create an image

It is also used in sonar and echo-sounding

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20
Q

What happens when a sound wave hits a solid

A

After being reflected many times some of the sound is absorbed, making objects in the particle vibrate and heat up

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21
Q

How does your ear detect sound

A

The outer ear gathers the sound wave and directs it to the ear drum which vibrates

The ear drum makes the ossicles vibrate which amplify the vibration, passing it on to the inner ear.

The Cochlea then transmits these movements of the oval window to small hairs through a liquid.
These hairs (cillia) are attached to sound-detecting cells which release a chemical that causes a nerve to travel to the brain (auditory nerve)

Your brain then turns this into sounf

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22
Q

Why can we only hear certain frequencies

A

Hairs on your cochlea have a natural frequency
They have different lengths and resonate with different frequencies

The range of sound you can hear depends on the size of the hairs

The smaller the hairs the lower the frequency

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23
Q

Why do we stop being able to hear high frequency sounds as we get older

A

The short hairs that detect high frequencies fall out

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24
Q

What are electromagnetic waves

A

Transverse waves caused by oscillating electric and magnetic fields
They do not require matter - they all travel through a vacuum

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25
Q

What is a vacuum

A

A region with no particles of matter

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26
Q

What speed do electromagnetic waves travel at

A

3×10^8 m/s
This is the speed of light (which is in the electromagnetic spectrum)

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27
Q

What are the waves in the electromagnetic spectrum

A

Radio
Micro
Infrared
Visual light
Ultraviolet
X-rays
Gamma

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28
Q

What colours make up visible light

A

Red
Orange
Yellow
Green
Blue
Indigo
Violet

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29
Q

How does the wavelength and frequency change in the visible spectrum

A

Red light - lower frequency, longer wavelength
Violet - higher frequency. Shorter wavelength

Going from R→V The frequency increases and the wavelength decreases

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30
Q

How does the frequency and wavelength change in the electromagnetic spectrum

A

From Radio to Gamma
Wavelength decreases
Frequency increases

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31
Q

Why is infrared called what it is and why is ultraviolet called what it is

A

William Herschel split light and recorded the temperature of each frequency
Red was the hottest but he realised that there was an area past red called infrared

He found ultraviolet in the same way (it was colder)

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32
Q

How do we know EM waves can travel through a vacuum

A

The sun emits ultraviolet waves and space is a vacuum

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33
Q

What is the name of the object that electromagnetic waves transfer energy to

A

Absorbers

34
Q

How are radio waves produced

A

An oscillating p.d across a wire causes electrons to move back and forth.

This produces a changing electric and magnetic field which releases radio waves

35
Q

How are radio waves detected

A

When they meet an aerial (metal object), the electric field causes electrons to flow, so an electrical signal can move (and produce an image)

36
Q

What electromagnetic waves are used in communication and examples

A

Microwaves - used in phones and communicating with satellite

Radio waves - sound and picture images are added to them to transmit television and radio signals

Infrared - remote controls use pulses of infrared to communicate with televisions

Visual light - used for ships to communicate

37
Q

How are microwaves used in microwave ovens

A

Water and fat in the food absorb microwaves which heats up the outside of the food
Conduction transfers energy to the middle

38
Q

What is conduction

A

Process of transferring heat between neighbouring particles

39
Q

What are the dangers of EM waves

A

The waves with higher frequencies are the most damaging

Ultraviolet, x-rays and gamma rays can all damage your DNA causing mutations and cancer

UV rays damage DNA in skin cells

Gamma rays can even kill cells

40
Q

What are the dangers of visible light, Infrared and microwaves

A

Visual light -Too much can cause blindness
Infrared - Can burn you
Microwaves - cause explosions (at a high enough frequency) in contact eith metals and internally heat cells

41
Q

What are the dangers of radio waves

A

There are no known dangers

42
Q

How are medical X-rays performed / what do they do

A

They were originally used to see bones and what is inside a person

Bones absorb X-rays while soft tissue like skin transmits it

Photographic film (placed behind the patient) darkens when in contact with x-rays, which can be used to see a persons internal structure
The white areas on photographic film are where the xrays have been absorbed by bones

43
Q

How are medical X-rays performed / what do they do

A

They were originally used to see bones and what is inside a person

Bones absorb X-rays while soft tissue like skin transmits it
Photographic film darkens when in contact with x-rays, which can be used to see a persons internal structure

44
Q

What does it mean if a wave is transmitted

A

It moves through the medium (refracted)

45
Q

What does it mean if a wave is reflected

A

The waves bounce off the surface in a different direction - no energy is absorbed

46
Q

What does it mean if a wave is absorbed

A

Energy is transferred from the wave to a medium

47
Q

How are X-rays used in CT scans

A

There are different rates of absorption within the body
The points where x-rays are absorbed are used to create a 3D image

(Similar to ultrasound)

48
Q

How are gamma rays used in medical imaging

A

It is used for imaging organs, e.g.the kidney
A patient is injected with radioactive tracers that emit gamma rays - that are transported to the target organ

By detecting the emitted gamma rays an image can be produced.

49
Q

What is thermography

A

Taking images using a thermal imaging camera

50
Q

What do thermal imaging cameras do

A

They detect infrared radiation which all objects constantly emit

The level of radiation detected depends on the temperature of the surface

Cooler surfaces are blue and hotter ones are red.

51
Q

What is a thermogram and what is there medical use

A

An image that shows different temperatures

They are used to detect inflammation or infection, where the IR levels will be higher than expected

52
Q

What are ray diagrams

A

Diagrams that show what happens when electromagnetic waves meet a boundary

53
Q

How do you draw ray diagrams

A

Draw a normal 90° to the surface the wave is coming intact with

Draw the incident wave (the wave that hits the surface)

The draw the lines that show whether the wave has been reflected or refracted

The reflected wave will bounce off the surface at the same angle the incident wave hit it

54
Q

What does it mean if something is resonant

A

It is oscillating at the same frequency as the object causing it to oscillate

55
Q

What three things can happen to EM waves when they hit a surface

A

They are
Absorbed
Transmitted
Reflected

56
Q

Why are radio waves reflected in the atmosphere

A

The earth is curved
To send radio waves over long distances they can be reflected in the ionosphere as they have a long enough wave length

57
Q

How can microwaves be used to communicate with satellites

A

They can travel through the ionosphere as they have a high enough frequency

58
Q

How do EM waves interact with walls (e.g house walls)

A

Walls transmit radio and microwaves, allowing your phones and tvs to work

They absorb visible light and ultraviolet

59
Q

Which EM waves does the atmosphere absorb

A

X-rays and gamma rays

However some rocks emit gamma rays

60
Q

What is a lens

A

A piece of transparent material that refracts light in a specific way.

Each lens refracts with a specific power

61
Q

How do you find the power of a lens

A

1 ÷ focal length (m)

The power of a lens is measured in Dioptres

62
Q

What are convex (converging lenses) and what are they used for

A

These lenses are thicker in the middle and reflect rays onto a principle focus, or focal point.

They are used to fix long sight, as they refract they light more, so close objects can be seen

63
Q

What are concave (diverging lenses) and what are they used for

A

Lenses which are thinner in the middle and thicker on the outside
They refract parallel waves away from the focal point

Used to fix long sight as the light is normally refracted too much

64
Q

What is the focal length

A

Distance between the centre of the lens and the focal point

65
Q

What is a virtual image

A

An image produced (often by a mirror) that cannot be seen / projected on a screen

66
Q

What is a real image

A

An image that can be projected on a screen

67
Q

What determines whether an image will be real or visual in a convex lens

A

If the object is in front of the principle focus it will be a virtual image

If it is further away a real image can be formed

68
Q

What is the principle axis

A

The line passing through the optical center

69
Q

What is the optical centre

A

The centre of a lens

70
Q

How can ray diagrams be used to predict where the image of the lens is

A

Draw a ray from the top of the object to the lens, parallel to the principal axis and from the lens to the focal point

Draw a ray from the top of the object, through the lens at the optical centre

Where the rays cross or appear to come from is where the image is

71
Q

What types of images can convex lenses produce

A

Magnifying glass - virtual, magnified, upright

Camera / eye - real diminished inverted

72
Q

What does it mean if an image is inverted

A

its upside down
The image is facing the opposite way to the object

73
Q

What type of images do concave lenses produce

A

Spy holes in doors - virtual, diminished, upright

Back windows of coaches - virtual diminished upright

They are always virtual diminished and upright

74
Q

How are rainbows formed

A

Light is made of different frequencies that travel at different speeds
Each frequency is refracted differently

Passing through a raindrop causes the light to refract as it has entered a denser medium - similar to a prism

This creates a rainbow

75
Q

What is dispersion (light)

A

When white light is spread out into a spectrum

76
Q

How do we see colour

A

The colour of an object is the colour that an object reflects

Grass appears green as it reflects all frequencies of light other than green

77
Q

How do filters work (light)

A

A red filter absorbs all frequencies of light except red.

Red light can still be transmitted while the others cant

78
Q

What is specular reflection

A

On a smooth surface, the reflected waves are all at the same angle as the incident rays

Specular reflection allows you to see images in paler

79
Q

What is the law of reflection

A

The angle of incidence is equal to the angle of reflection

80
Q

What is diffuse reflection

A

There is irregular scattering due to an uneven surface.

Each ray hits the surface at a different angle and is therefore reflected differently

Images can never be seen where there is diffuse reflection

(A) Physics (10 decks)

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