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Physics > 3 Waves > Flashcards

3 Waves Flashcards

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1
Q

Waves

A

Oscillations in a medium that transfer energy not matter. Examples are water waves, electromagnetic waves and sound waves.

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2
Q

What do waves consist off

A

The ripples are made up of a series of peaks (high points) and troughs (low points) moving outwards from the source of a disturbance

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3
Q

Wavelength

A

The wavelength is the distance between any two similar points in a wave pattern such as two adjacent crests. The wavelength can also be measured between two adjacent troughs.

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4
Q

Amplitude

A

The amplitude of the wave is a measure of the energy it carries. For a transverse wave the amplitude is the height of the wave above the central position.

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5
Q

Frequency

A

Number of waves produced in each second. Measured in HERTZ(Hz)

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6
Q

Period(time)

A

Time taken for one whole wave to pass a period in space

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7
Q

The wave formula

A

v=fλ
wave speed = frequency × wavelength

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8
Q

Transverse Wave

A

Particles at right angles to the wave’s direction of travel(Propagation)
S waves

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9
Q

Longitudinal waves

A

Particles parallel to the waves direction of travel
P waves

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10
Q

Law of reflection for plane mirrors

A

The angle of incidence is equal to the angle of the reflection

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11
Q

The three most important behaviours of waves are:

A

reflection: a wave ‘bounces’ off a boundary
refraction: a wave moves from one medium to another
diffraction: a wave spreads as it moves through a gap.

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12
Q

Incident wave

A

The path of a wave which travels from the source.

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13
Q

Reflected wave

A

The path of a wave which has reflected from a surface.

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14
Q

Refraction

A

Refraction is the bending of light as it travels between 2 different mediums with different refractive index ( the higher the stronger)

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15
Q

Refractive index

A

n = Sin I ÷ Sin R

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16
Q

Diffraction of waves

A

When a wave passes through a gap, the wave spreads outwards from the gap. This effect is called diffraction.

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17
Q

Changes in refractive index

A

Low to High: Bend towards normal
High to Low: Bend away from normal

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18
Q

Normal

A

A line drawn perpendicular to a surface from which angles of incidence, reflection and refraction are measured.

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19
Q

Angle of Incidence

A

The angle at which a wave or ray approaches a boundary or surface. Measured from the normal.

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20
Q

Angle of reflection

A

The angle at which a wave or ray leaves a boundary or surface after being reflected. Measured from the normal.

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21
Q

Virtual image

A

An image formed by a lens which cannot be projected onto a screen as the rays of light only appear to pass through it. Virtual images are formed by mirrors and some lenses.

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22
Q

Real image

A

An image formed by a lens which can be projected onto a screen. Rays of light pass through the points on a real image.

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23
Q

Formation of an image in a plane mirror

A

An image is formed when all the rays from one point on the object are reflected by the mirror, and then seem to come from a single point behind the surface of the mirror.

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24
Q

Refraction of a light ray will cause it to change direction towards or away from a normal

A

When light moves from air into glass, the light will slow down. This causes it to change direction towards the normal.
When light moves from a glass block into air, then it will speed up. This causes a change in direction away from the normal.
If the ray enters or leaves the block normal to the surface, then there is a change of speed, but the ray continues to travel in the same direction.

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25
Q

Internal reflection

A

When light moves across a boundary between materials some of it is reflected back from the boundary.

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26
Q

Total internal reflection

A

When light is perfectly reflected as its reaches a boundary. The effect only happens if the angle of incidence is above the critical angle.

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27
Q

Critical angle

A

The largest angle of incidence which allows light to leave a material. Above this angle the light will be totally internally reflected.

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28
Q

critical angle

Refractive index

A

n=1/sin c
C= critical angle

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29
Q

Optical fibres

A

Total internal reflection is a very useful effect, as it allows us to direct light to travel in any path we want. This effect is used in optical fibres. These are very thin glass or plastic tubes which can bend.

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30
Q

Converging lens

A

A lens which converges (brings together) rays of light.

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31
Q

Diverging lens

A

A lens which diverges (spreads out) rays of light.

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32
Q

Focal length

A

The distance between the centre of a lens and it’s principal focal. Measures along the principal axis.

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33
Q

Enlarged

A

An image formed by a lens that is larger than the object.

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34
Q

Upright

A

An mage formed by a lens that is the same way up as the object.

35
Q

Inverted

A

An image is formed by a lens which is upside down compared to the object.

36
Q

Cornea

A

A tough, colourless and transparent outer layer covering the iris and pupil of the eye. Most refraction of light happens through the cornea.

37
Q

The lens of the eye

A

This is a converging lens made from a tough, transparent material. Tiny muscles which surround it can be used to stretch it to make it thinner. This increases its focal length and allows us to focus on objects which are further away.

38
Q

Short-sightedness

A

Over time, the lens in your eye may become difficult to stretch and so it cannot be made thin enough by the eye muscles. This results in a condition known as short-sightedness. The thick lens causes light for distance objects to be focused in front of the retina so we cannot see them clearly. The far point of the eye is no longer at infinity and may only be a few metres away.

39
Q

Long-sightedness

A

Some people develop long-sightedness. This is a condition where the lens cannot be made thick enough, or the eyeball is too short. The result is that the light from nearby objects is focused on a point behind the retina giving a blurred image. The near point becomes further away from the eye, meaning that you might have to hold writing further away to read it easily.

40
Q

Dispertion

A

he separation of white light into its constituent colours due to the differ speeds of different wavelengths of light passing through a material.

41
Q

Visible light

A

Electromagnetic waves with a wavelength that we can see.

42
Q

Infrared

A

Electromagnetic waves used for cooking (grilling) and in optical fibres for communications. Emitted by all objects but more radiation is emitted by hotter objects.

43
Q

Ultraviolet

A

Electromagnetic waves emitted from very hot objects like the Sun. Can cause sunburn, skin cancer and damage eyes.

44
Q

Radio waves

A

A type of transverse wave that consists of vibrating electric and magnetic fields. Electromagnetic radiation does not need a medium to travel through and travels at the highest speed possible in a vacuum.

45
Q

The rule with waves and vacuums

A

All electromagnetic waves travel at the same speed in a vacuum – at 3.0×108 m/s (300000000 m/s)
. This is the fastest speed anything can possibly travel – fast enough for an electromagnetic wave to travel around the circumference of the Earth seven and a half times in one second.

46
Q

Microwaves

A

Electromagnetic waves with a wavelength of a few cm or mm. Used for cooking and communication technology.

47
Q

X-rays

A

High energy electromagnetic waves which can pass through some materials but not others. Used to take pictures of bones, teeth for example. Can be harmful.

48
Q

Gamma rays

A

Electromagnetic waves are emitted by radioactive materials.

49
Q

Use of Radio waves

A

Communication (Radio and TV), RFID tags

50
Q

Use of Microwaves

A

Heating food, Cell phone signals, Satelites

51
Q

Use of IR

A

Heating, Remote control, Alarms, Thermal imaging

52
Q

Use of Visible Light

A

Sight, photography/ film, Illumination

53
Q

Use of UV

A

Sterilisation, forgeing detection

54
Q

Use of X-rays

A

Medical imaging, security scanner

55
Q

Use of Gamma rays

A

Quality control, Imaging, cancer treatments, food sterilisation

56
Q

Dangers of Microwaves

A

Heating of cells

57
Q

Dangers of Infrared

A

Skin burns

58
Q

Dangers of X-rays and Gamma rays

A

Overexposure can cause DNA damage–> Mutilation(general damage)

59
Q

Dangers of UV

A

Damage to cells, DNA, Eyes –> cancer or eyesight degradation

60
Q

Anauloge

A

A continuous signal that can have any value and be increased or decreased by infinitely small divisions.

61
Q

Digital

A

A signal that has a set of discrete values, normally 0 or 1.

62
Q

Regeneration

A

A way of removing noise from a digital signal so it can be transmitted further.

63
Q

Medium

A

The material through which a wave passes. The plural of medium is ‘media’. Waves travel at different speeds in different media.

64
Q

Pitch

A

How we perceive the frequency of a sound wave. When a sound wave has a high frequency (for example 1000 Hz), we hear it as a high-pitched sound; when the frequency is low (e.g. 20 Hz), we hear a low-pitched sound.

65
Q

Sound

A

When an object, like the string of a guitar vibrates, it produces a sound wave which travels through the air. The wave travels from the source (the guitar string) through a medium (the air) and reaches a detector (our ear). The wave then causes our ear drum to vibrate, and this vibration passes through a series of tiny bones into our inner ear, stimulating nerve cells to send electrical signals to our brain. These signals cause the sensation of sound.

66
Q

The properties of the sound wave can vary depending on how the object producing the sound is vibrating.

A

If the vibrations are made larger, by plucking the string harder, then the amplitude of the sound wave will become greater. Increasing the amplitude increases the energy transfer and so the sound will be louder.
If the object is made to vibrate back and forth more times each second, then it produces vibrations at a higher frequency. The pitch of the sound we hear will be higher.

67
Q

Changing the properties of a sound wave.

A

Change to the source of vibration What happens to the sound wave? What happens to what we hear?
faster vibrations increased frequency increased pitch
larger vibrations increased amplitude increased loudness

68
Q

How sound waves travel

A

Sound waves are a type of longitudinal wave. The particles which form the wave move back and forth in the same direction as the wave travels. As the wave passes through the air, it produces regions where the air particles are compressed closer together, known as compressions , and regions where the air particles are spread out slightly further than normal, known as rarefactions

69
Q

Compressions

A

A region of air (or another material) where the particles are closer together than normal due to a sound wave passing through it.

70
Q

Refractions

A

A region of air (or another material) where the particles are further apart than normal due to a sound wave passing through it.

71
Q

Reflection of sound waves

A

Sound waves can reflect when they reach a boundary between materials. This happens when a sound wave moving through the air reaches a hard surface, such as a wall. The wave hits the wall and is reflected away from the wall, back towards its source. The reflected sound wave is called an echo.

72
Q

The speed of sound in different media

A

Sound waves travel at different speeds in different materials. Many factors affect this speed, including the density and elasticity of the materials. In general, however, sound travels slowest in gases, faster in liquids and fastest of all in solids.

73
Q

How to measure the speed of sound

A

A better approach to measuring the speed of sound is to use an electronic system to start and stop the stopwatch. This eliminates timing errors and gives a more accurate measurement of the speed of sound.

74
Q

what happens if there is no medium for sound to travel

A

Sound waves can only travel through a medium made up of particles, they cannot exist where there are no particles. A vacuum is completely empty space and so sound waves cannot pass through it at all. This means that sound does not travel through empty space.

75
Q

Ultrasound

A

Sound waves with a frequency above 20 000 Hz. Humans cannot hear sound waves above this frequency.

76
Q

Uses of ultrasound

A

Using ultrasound to measure distances
Sonar
Using ultrasound to analyse materials for damage
Using ultrasound in medical scanning

77
Q

Monochromatic

A

is light of a single frequency

78
Q

Speed of light

A

3 × 10^8 (m / s)

79
Q

Speed of sound

A

Air= 343m/s
Water= 1500m/s

80
Q

Refractive index

A

speed of light in vacuum ÷ Speed of light in a medium

81
Q

Wavelength of the electromagnetic spectrum from high to low
Frequency of the electromagnetic spectrum from low to high

A

Radio
Microwave
Infrared
Visible light
Ultra-violet
X-rays
Gamma rays

82
Q

Sound wave:
Compression
Refraction

A

(region where) particles are close(r) together (than normal) OR (region where) there is a great(er) pressure (than normal)

(region where) particles are further / far apart (than normal) OR (region where) there is a low(er) pressure (than normal)

83
Q

Wavelength and frequncey

A

wave length ^-!
Radio
Micro
Infrared
Visible
Ultraviolet
Xrays
Gamma

Physics (6 decks)

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