Waves

Question 1

What is a wave?

Answer 1

A vibration that transfers energy without transferring matter

Question 2

What is a transverse wave?

Answer 2

A wave where the oscillations are perpendicular to the direction of energy transfer of the wave

Question 3

What is a longitudinal wave?

Answer 3

A wave where the oscillations are parallel to the direction of energy transfer of the wave

Question 4

What happens when waves travel through a medium?

Answer 4

The particles vibrate and transfer energy between each other but they stay in the same place

Question 5

What are crests and troughs?

Answer 5

Points of maximum positive and maximum negative displacement from the particles rest position

Question 6

What is the amplitude of a wave?

Answer 6

The maximum displacement of a point from its undisturbed position

Question 7

What is the equation for the period of a wave?

Answer 7

Period= 1 over frequency.

Question 8

What is the wavelength?

Answer 8

The distance between the same point on two adjacent waves.

Question 9

What is the frequency?

Answer 9

The number of complete waves passing a certain point per second.

Question 10

What is frequency measured in?

Answer 10

Hertz (Hz)

Question 11

How can the speed of sound be measured using an oscilloscope?

Answer 11

Set up oscilloscope so the detected waves at each microphone as shown as separate waves, slowly move microphones away until two waves are aligned, measure distance between microphones to find wavelength then use formula

Question 12

What can happen when waves arrive at a boundary between two different materials?

Answer 12

They can be absorbed by the material they are trying to pass into, they can be transmitted and keep on travelling (often leading to refraction) or they can be reflected

Question 13

What is the rule for all reflected waves?

Answer 13

Angle of incidence = angle of reflection

Question 14

What is the angle of incidence?

Answer 14

The angle between the incoming wave and the normal

Question 15

What is the angle of reflection?

Answer 15

The angle between the reflected wave and the normal

Question 16

What is the normal?

Answer 16

An imaginary line that’s perpendicular to the surface at the point of incidence, normally shown as a dotted line

Question 17

What is specular reflection?

Answer 17

When a wave is reflected in a single direction by a smooth surface

Question 18

What is diffuse reflection?

Answer 18

When a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions

Question 19

Why does diffuse reflection happen?

Answer 19

Because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray

Question 20

What are EM waves?

Answer 20

Waves that are transverse and transfer energy from a source to an absorber and all travel at the same speed through air or a vacuum

Question 21

Give the EM spectrum, with each wave increasing frequency and decreasing wavelength

Answer 21

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays

Question 22

Why are there such a large range of frequencies in the EM spectrum?

Answer 22

Because EM waves are generated by a variety of changes in atoms and their nuclei

Question 23

What is refraction?

Answer 23

When a wave crosses a boundary between materials at an angle and it changes direction

Question 24

What does how much a wave refracts depend on?

Answer 24

How much the wave speeds up or slows down, which depends on the density of the two materials

Question 25

How does speed affect a wave when crossing a boundary?

Answer 25

If it slows down it will bend towards the normal and if it speeds up it will bend away from the normal

Question 26

How is wavelength and frequency affected when a wave is refracted?

Answer 26

Wavelength changes but frequency stays the same

Question 27

What is the optical density of a material?

Answer 27

A measure of how quickly light can travel through it; the higher the optical density, the slower light waves travel through it

Question 28

How do you construct a ray diagram for a refracted ray of light?

Answer 28

Draw a horizontal boundary, then draw the normal perpendicular to it, draw an incident ray that meets the normal at the boundary, then draw the refracted ray on the other side of the boundary.

Question 29

How does the optical density affect the size of the angle of refraction in comparison to the size of the angle of incidence?

Answer 29

If the second material is optically denser than the first, the refracted ray bends towards the normal and the angle of refraction will be smaller than the angle of incidence

Question 30

What are EM waves made up of?

Answer 30

Oscillating electric and magnetic fields

Question 31

How are radio waves produced by an alternating current in an electrical circuit?

Answer 31

When transmitted radio waves reach a receiver, they are absorbed, the energy carried by the waves is transferred to the electron sin the material of the receiver, causing the electrons to oscillate, generating an alternating current which has the same frequency as the radio wave that generated

Question 32

How long are the wavelegnths of radio waves?

Answer 32

Around 10 cm or longer

Question 33

Why can long-wave radio be transmitted around the world?

Answer 33

The longer wavelengths diffract around the curved surface of the earth, as well as diffracting around things like hills or into tunnels

Question 34

Why can short-wave radio signals be received at long distances away from the transmitter?

Answer 34

They are reflected from the ionosphere (an electrically charged layer in the earth’s upper atmosphere)

Question 35

How does satellite TV work (in terms of waves)?

Answer 35

Microwaves are set from a transmitter on earth into space, where they are picked up by a satellite orbiting above earth. The satellite transmits the signal back to earth in a different direction whee it is received by a satellite dish on the ground

Question 36

How do microwave ovens work?

Answer 36

The microwaves penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up, which cooks the rest of the food

Question 37

What uses does infrared radiation have?

Answer 37

Infrared cameras (which detects the IR radiation and turns it into an electric signal) , cooking food as absorbing IR radiation causes an object to get hotter and electric heaters which emit IR radiation

Question 38

How do fibre optic cables work?

Answer 38

Visible light rays are bounced back and forth until they reach the end of the fibre. The light is not easily absorbed or scattered as it travels along a fibre

Question 39

Why do fluorescent colours look so bright?

Answer 39

Fluorescence is a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted

Question 40

What are the uses of UV radiation?

Answer 40

Fluorescent lights (same as colours except the visible light is radiated out by a layer as phosphorus), security pens which only show up under UV, suntans (from the sun) and UV lamps

Question 41

How do X-rays produce an image of bones in a body?

Answer 41

They easily pass through flesh but not bones so the amount of radiation that is absorbed can allow you to build up an image

Question 42

How are X-rays and gamma rays sued to treat cancer?

Answer 42

High doses of these rays can kill all living cells, so they are carefully directed towards the cancer cells to avoid killing healthy cells

Question 43

Why is gamma radiation a good medical tracer?

Answer 43

It can pass out through the body to be detected

Question 44

How to radiographers keep their exposure to X-rays and gamma rays to a minimum?

Answer 44

They wear lead aprons and stand behind lead screen or leave the room

Question 45

What types of waves can harm people and why?

Answer 45

High frequency waves as they transfer a lot of energy. This includes UV which damages surface cells (sunburn and aging), X-rays and gamma rays which both are ionising radiation (causing gene mutation or cell destruction)

Question 46

What is radiation dose?

Answer 46

A measure of the risk or harm from the body being exposed to radiation, which is measured in sieverts or millisieverts

Question 47

What is a convex lens?

Answer 47

A lens which bulges outward, causing rays of light parallel to the axis to be brought together at the principal focus

Question 48

What is a concave lens?

Answer 48

A lens that caves inwards, causing parallel rays of light to spread out

Question 49

What is the axis of a lens?

Answer 49

A line passing through the middle of the lens

Question 50

What is the principal focus of a convex lens?

Answer 50

Where rays hitting the lens parallel to the axis all meet

Question 51

What is the principal focus of a concave lens?

Answer 51

The point where rays hitting the lens parallel to the axis appear to all come from (behind the lens)

Question 52

What is the focal length?

Answer 52

The distance from the centre of the lens to the principal focus

Question 53

What are the three rules for refraction in an convex lens?

Answer 53

An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
An incidence tray passing through the centre of the lens carries on in the same direction

Question 54

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

Answer 54

An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus
An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries on in the same direction

Question 55

What is a real image?

Answer 55

Where the light from an object comes together to form an image on a ‘screen’ (like an image formed on the eye’s retina)

Question 56

What is a virtual image?

Answer 56

Where the rays are diverging, so the light from the object appears to be coming from a completely different place (e.g. looking in a mirror or magnifying glass)

Question 57

What three things do you need to do to describe an image properly?

Answer 57

How big it is compared to the object, whether it is upright or inverted compared to the object and whether it is real or virtual

Question 58

How do you draw a ray diagram for an image through a convex lens?

Answer 58

Pick a point at the top of the object, then draw an ray going from the object to the lens parallel to the axis of the lens, draw another ray from the top of the object going through the middle of the lens, draw a refracted ray passing through the principal focus, mark where the rays meet (at the top) then repeat the process for a point at the bottom

Question 59

How do you draw a ray diagram for an image through a convex lens?

Answer 59

Pick a point at the top of an object, draw a ray going from the object to the lens parallel to the axis, draw another ray from the top of the object going right through the middle of the lens, draw ray from the principal focus, make it dotted before it reaches the lens, mark where the refracted meet, then repeat the process for a point on the bottom of the object

Question 60

What do concave lenses always create?

Answer 60

A virtual image: the image is right way up, smaller than the object and on the same side of the lens as the object

Question 61

How do magnifying glasses work?

Answer 61

By creating a magnified virtual image

Question 62

Give the magnification formula

Answer 62

magnification = image height / object height

Question 63

What is a primary colour?

Answer 63

Colours that can’t be made by mixing any other colours together: red, green and blue

Question 64

What are opaque objects?

Answer 64

Objects that do not transmit light: when visible light waves hit them, they absorb some wavelengths of light and reflect others

Question 65

What does the colour of an opaque object depend upon?

Answer 65

It depends upon which wavelengths of light are most strongly reflected. If it is not a primary colour, it may be reflecting either the wavelengths of light corresponding to that colour or the wavelengths of the primary colours that can mix together to make that colour

Question 66

How do white and black objects reflect light?

Answer 66

White objects reflect all of the wavelengths of visible light equally and black objects absorb all wavelengths of visible light; your eyes see black as the lack of any visible light

Question 67

What is a translucent or transparent object?

Answer 67

They are objects that transmit light. Some wavelengths of light may be absorbed or reflected; the object’s colour is related to the wavelengths of light transmitted and reflected by it

Question 68

How do colour filters work?

Answer 68

They filter out different wavelengths so that only certain colours (wavelengths) are transmitted so the rest are absorbed

Question 69

What is a primary colour filter?

Answer 69

A colour filter that only transmits that colour e.g. is white light was shone at a blue colour filter, only blue light would be let through

Question 70

How do colour filters work that aren’t for primary colours?

Answer 70

They let through both the wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour

Question 71

Which objects emit and absorb IR?

Answer 71

All objects; IR is emitted form the surface of an object

Question 72

How much IR radiation does an object hotter or colder than it’s surroundings emit?

Answer 72

A hotter object emits more IR radiation than it absorbs as it cools down whereas a colder object absorbs more than it emits as it warms up

Question 73

How much IR radiation is absorbed and emitted by an object at a constant temperature?

Answer 73

It emits infrared radiation at the same rate that it is absorbing it

Question 74

Which types of surfaces are better at absorbing and emitting IR?

Answer 74

Black and matt surfaces

Question 75

What is a Leslie cube?

Answer 75

A hollow, watertight metal cube whose four vertical faces have different surfaces

Question 76

What is a perfect black body?

Answer 76

An object that absorbs all radiation that hits it; no radiation is reflected or transmitted. A perfect black body is the best possible emitter of radiation

Question 77

What does the intensity and distribution of the wavelengths emitted by an object depend on?

Answer 77

The object’s temperature; intensity is the power per unit area. AS temperature increases, so does intensity, however, the intensity increases more rapidly than longer wavelengths, causing the peak wavelength to decrease

Question 78

What does the overall temperature of the earth depend on?

Answer 78

The amount of radiation is reflects, absorbs and emits

Question 79

Why does the overall temperature of the earth stay fairly constant?

Answer 79

During the day, there is an increase in temperature as lots of radiation is transferred to the earth from the sun and absorbed but at night, the temperature decrease as less radiation is being absorbed than emitted

Question 80

Why do changes to the atmosphere cause a change to the earth’s overall temperature?

Answer 80

If the atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again (global warming)

Question 81

What are sound waves causes by?

Answer 81

Vibrating objects: these vibrations are passed through the surrounding medium as a series of compressions are rerefractions

Question 82

What medium do sound waves travel fastest in and why?

Answer 82

Solids as it is easier for the particles to pass the vibrations to one another

Question 83

Why can’t sound waves travel in space?

Answer 83

It is a vacuum, meaning that there are no particles to vibrate

Question 84

How does the human ear hear sound?

Answer 84

Sound waves that reach the ear drum cause it vibrate, vibrations are passed on to tiny bones called ossicles, through the semicircular canals and to the cochlea, cochlea turns these into electrical signals, get sent to brain and allow you to sense the sound

Question 85

What frequencies can humans hear?

Answer 85

Anything in the range of 20 Hz - 20 kHz

Question 86

What is human hearing limited by?

Answer 86

The size and shape of the ear drum as well as the structure of all the parts within the ear that vibrate to transfer the energy from the sound wave

Question 87

What are echoes?

Answer 87

Sound waves reflected by hard, flat surfaces

Question 88

How is speed affected when a sound wave enters a denser material and why?

Answer 88

The sound wave speeds up because when a wave travels into a different medium, it’s wavelength changes but it’s frequency remains the same so it’s speed must also change

Question 89

How is ultrasound created?

Answer 89

Electrical devices can be made to produce electrical oscillations over a range of frequencies. These can easily be converted into mechanical vibrations to produce sound waves beyond the range of human hearing

Question 90

What is partial reflection?

Answer 90

When a wave passes from one medium to another, some of the wave is reflected off the boundary between the two media and some is transmitted

Question 91

How can ultrasound be used to measure how far away a boundary is?

Answer 91

When you point a pulse of ultrasound at an object, wherever there are boundaries, some of the ultrasound gets reflected back. The time it takes for the reflections to reach a detector can be used to measure the distance

Question 92

How is ultrasound used in medical imaging?

Answer 92

Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media, some of the wave is reflected back and detected. The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.

Question 93

How is ultrasound used in industrial imaging?

Answer 93

Ultrasound waves can be used to find flaws in material. When entering a material, they will usually be reflected by the far side of the material. If there is a flaw (a crack) inside the object, the wave will be reflected sooner

Question 94

How are seismic waves produced and detected?

Answer 94

They are caused by an earthquake somewhere and can be detected by seisometers

Question 95

What do seismologists measure?

Answer 95

The time it takes for the shock waves to reach the seisometers and which parts of earth don’t receive the shock waves at all

Question 96

What happens if a seismic wave reaches a boundary?

Answer 96

Some waves will be refracted and some will be absorbed. If the waves are refracted, they change speed gradually, resulting in a curved path, but if the properties change abruptly, the wave speed changes abruptly, resulting in a path with a kink

Question 97

What are the two types of seismic waves?

Answer 97

P waves and S waves

Question 98

Describe P waves

Answer 98

They are longitudinal, travel through solids and liquids and are faster than S waves

Question 99

Describe S waves

Answer 99

They are transverse and can’t travel through liquids or gases. They’re slower than S waves

Question 100

What can observing how seismic waves are absorbed and refracted tell scientists?

Answer 100

They can work out where the properties of earth change dramatically, helping scientists to build up the internal structure of the earth