Waves

Question 1

what do waves do?

Answer 1

transfer energy and information without transferring matter; the particles oscillate about a fixed point

Question 2

what are features of transverse waves?

Answer 2

• have peaks and troughs
• vibrations are at right angles to the direction of travel
• an example = light

Question 3

what are features of longitudinal waves?

Answer 3

• consists of compressions (particles pushed together) and refractions (particles moved apart)
• vibrations are in the same direction as the direction of travel
• an example = sound

Question 4

amplitude definition

Answer 4

the distance from the equilibrium position to the maximum displacement

Question 5

wavefront definition

Answer 5

a line joining points on a wave at the same point in their wave cycle at a give time

Question 6

frequency definition

Answer 6

the number of waves that pass a single point per second

Question 7

wavelength definition

Answer 7

the distance between a point on one wave and the same point on the next wave

Question 8

time period definition

Answer 8

the time taken for one complete wave to pass a fixed point

Question 9

what is the speed of a wave equal to?

Answer 9

the product of the frequency and wavelength

Question 10

what is frequency of a wave equal to?

Answer 10

the reciprocal of the time period (1/time period)

Question 11

what is frequency measured in?

Answer 11

hertz (Hz)

Question 12

what is the doppler effect?

Answer 12

• if a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength due to the doppler effect
• this is because the wave fronts either get bunched together or spaced apart
• an example of this is when the siren of an ambulance is high-pitched as it approaches you, and low-pitched as it goes away

Question 13

when can all waves be reflected?

Answer 13

when they travel from a medium of low optical density (such as air) to one of much higher optical density (such as glass)

Question 14

what does the law of reflection state?

Answer 14

angle of incidence = angle of reflection

Question 15

when a wave is reflected what happens to the frequency, wavelength and speed

Answer 15

they are all unchanged

Question 16

when can all waves be refracted?

Answer 16

when the speed of a wave changes when it enters a new medium

Question 17

what happens to the speed of a wave when it enters a denser medium?

Answer 17

its speed decreases and it bends towards the normal

Question 18

what happens to the speed of a wave when it enters a less dense medium?

Answer 18

its speed increases and it bends away from the normal

Question 19

what happens to the frequency, wavelength and velocity of a wave when it is refracted?

Answer 19

• the frequency stays the same
• the wavelength changes
• as a result, the velocity must change

Question 20

what is the order of the electromagnetic spectrum?

Answer 20

radio -> microwave -> infrared -> visible -> ultraviolet -> x-ray -> gamma ray

Question 21

as the EM spectrum goes from radio to gamma ray, what happens to the wavelength and frequency?

Answer 21

the wavelength decreases and the frequency increases

Question 22

what speed do all the EM waves share?

Answer 22

all electromagnetic waves travel with the same high speed in a vacuum and the same speed in air

Question 23

what are radio waves used for and why?

Answer 23

• radio and television communicators
• they have a long wavelength and are reflected by a layer of the atmosphere called the ionosphere

Question 24

what are microwaves used for and why?

Answer 24

• satellite transmissions and in cooking
• they have a greater frequency (shorter wavelength) and they are more penetrating so can pass through the ionosphere and penetrate deep into food

Question 25

what is infrared radiation used for?

Answer 25

heaters and night vision equipment

Question 26

what is visible light used for?

Answer 26

fibre optics and photography

Question 27

what is ultraviolet light used for?

Answer 27

fluorescent lamps

Question 28

what are x-rays used for and why?

Answer 28

- medical imaging and in security - they have a very short wavelength and high frequency and they can penetrate material easily

Question 29

what is gamma radiation used for and why?

Answer 29

- sterilising food and medical equipment - it has high energy

Question 30

what are the hazards of microwaves?

Answer 30

they can cause internal heating of body tissues

Question 31

what are the hazards of infrared radation?

Answer 31

they can cause skin burns

Question 32

what are the hazards of ultraviolet light?

Answer 32

ultraviolet light exposure increases the risk of skin cancer and blindness

Question 33

how can you prevent the hazards of UV light?

Answer 33

wear sun cream and sun glasses to prevent over-exposure in summer

Question 34

what are the hazards of x-rays and gamma rays?

Answer 34

they are ionising radiation that can cause mutations leading to cancer

Question 35

how can you prevent the hazards of x-rays and gamma rays?

Answer 35

- exposure to these kinds of radiation should be minimised - you can do this by using protective shielding made of very dense materials such as lead

Question 36

what are light waves?

Answer 36

transverse waves that can be reflected and refracted

Question 37

how can reflection of light be shown?

Answer 37

when light reflects at a plane mirror and forms an image - this can be represented by a ray diagram

Question 38

how can refraction of light be shown?

Answer 38

when light is passed through a glass slab at an angle to its normal

Question 39

what happens to the angle of incidence when a light enters a more optically dense medium?

Answer 39

the angle of incidence is greater than the angle of refraction

Question 40

what happens to the angle of incidence when a light enters a less optically dense medium?

Answer 40

the angle of incidence is smaller than the angle of refraction

Question 41

what does snell's law state?

Answer 41

it relates the angle of incidence and the angle of refraction to the refractive index of a medium

Question 42

what is total internal reflection?

Answer 42

- at a certain angle of incidence called the critical angle, the light will travel along the boundary between the two media - total internal reflection occurs when the angle of incidence is greater than the critical angle and the light reflects back into the medium - for total internal reflection to occur, the light must be travelling from a more optically dense medium into a less optically dense medium (e.g. glass to air) - the critical angle can be related to the refractive index by: n = 1/sin C

Question 43

what is an optical fibre?

Answer 43

an optical fibre is a long thin rod of glass surrounded by cladding which uses total internal reflection to transfer information by light, even when bent

Question 44

what are optical fibres used for?

Answer 44

they are used extensively in medicine (endoscopes, inside body flexible cameras) and communications (high speed data transfer)

Question 45

what are sound waves?

Answer 45

longitudinal waves that can be reflected and refracted

Question 46

what is the range of audible frequencies for a healthy human ear?

Answer 46

20Hz to 20,000Hz

Question 47

how can you measure the speed of sound in air?

Answer 47

- you can make a noise at a known, large distance from a solid wall and record the time for the echo (reflected sound) to be heard - then use speed = distance/time (where distance is 2x length)

Question 48

what does an oscilloscope connected to a microphone show?

Answer 48

it can be used to display a sound wave and find its frequency and amplitude

Question 49

the greater the amplitude of a sound wave...

Answer 49

the louder it is

Question 50

the greater the frequency of a sound wave...

Answer 50

the higher its pitch