Waves

Question 1

what is wavelength? (λ)

Answer 1

distance from one peak to the next

Question 2

what is frequency? (f)

Answer 2

how many complete waves pass per second

Question 3

what is the measurement for frequency ?

Answer 3

hertz (Hz) 1 Hz = 1 wave per second

Question 4

What is amplitude ?

Answer 4

height of the wave (rest to crest) / (trough to rest)

Question 5

what is a period ? (T)

Answer 5

time (s) it takes for one complete wave

Question 6

Frequency =

Answer 6

1 / period ( time (T) )

Question 7

wave speed =

Answer 7

frequency x wavelength (v = f x λ)

Question 8

1 MHz = how many Hz?

Answer 8

1 000 000 Hz

Question 9

1 kHz = how many Hz?

Answer 9

1 000 Hz

Question 10

Most waves are …?

Answer 10

Transverse

Question 11

Give some examples of transverse waves

Answer 11

light and all other EM waves
slinky wiggled up and down
ripples on water

Question 12

Give some examples of longitudinal waves

Answer 12

sound and ultrasound
shock waves ( like seismic waves )
slinky pushed inwards

Question 13

Describe the vibrations in transverse waves

Answer 13

vibrations are at 90° to the direction energy is transferred by the wave

Question 14

Describe the vibrations in longitudinal waves

Answer 14

vibrations are along the same direction the wave transfers energy

Question 15

What is diffraction ?

Answer 15

waves bend around edges and through gaps
waves spread out
longer wavelength / narrow gap = more diffraction

Question 16

Visible light colours order

How do they link to wave length?

Answer 16

Red - longest wavelength
Orange 
Yellow
Green
Blue
Indigo
Violet - shortest wavelength

Question 17

Give the order of EM waves (including wavelength and frequency)

Answer 17

Radio waves (longest wavelength/lowest frequency) - microwaves - infra red - visible light - ultra violet - x rays - gamma rays (shortest wavelength/highest frequency)

Question 18

what speed do EM waves travel at ?

Answer 18

all travel same speed through free (vacuum)

they are also all transverse

Question 19

Describe radio waves

Uses ?

Answer 19

used for communications/TV/FM radio
long radio waves can travel around the world as they diffract around earths curve
short radio waves can also travel great distances as they reflect from the ionosphere

Question 20

what is the ionosphere ?

Answer 20

an electrically charged layer in Earth’s upper atmosphere

Question 21

Describe how microwave satellites work

Answer 21

used for satellite communication (like satellite TV)
signal transmitted to a transmitter in space
transmitter transmits signal to satellite dish on ground

Question 22

Describe how microwave ovens work

Answer 22

used for cooking, have different wave length to microwave communications
these are absorbed by water molecules in food and the energy is conducted or convected

Question 23

What are the uses for infrared radiation ?

Answer 23

used for heating and monitor temp
used in grills / toasters to cook food
used in radiators to radiate heat
used in night vision, turns infrared into electrical sign displayed on screen

Question 24

Describe how visible light signals work (optical fibres)

Uses ?

Answer 24

used for communication with light signals which carry data as pulses of light
they work by bouncing waves of light off sides of a narrow core
light enters at certain angle and is reflected repeatedly until comes out
used in telephone / internet cables and medical purposes (see inside body)

Question 25

Describe how visible light photography works

Answer 25

camera uses lens to focus light onto electronic sensor lens aperture controls how much light enters camera shutter speed determines how long sensor exposed to light

Question 26

What are the uses for ultraviolet ? How are they made safe ? Advantages ?

Answer 26

used in florescent lamps they use UV radiation to emit visible light safe to use as UV is absorbed by phosphor coating more energy-efficient than filament light bulbs

Question 27

What are the uses for X-Rays ? | How does it work ?

Answer 27

used to see inside things - diagnose broken bones x-ray radiation is directed to object onto detector plate brighter bits are where less X-rays got through (bones/metal) x-rays may cause mutations like cancer

Question 28

How are Gamma rays useful ?

Answer 28

gamma rays kill all microbes so useful for sterilising medical equipment and food it makes the food fresh for longer

Question 29

how can microwaves be dangerous?

Answer 29

heat human body tissue internally by increasing vibrations of molecules

Question 30

how can infrared be dangerous?

Answer 30

causes skin burns by making surface (skin) molecules vibrate more

Question 31

how can ultraviolet be dangerous?

Answer 31

damages surface cells and can cause blindness | is ionising so can knock off electrons, causing cell mutation (cancer)

Question 32

how can gamma rays be dangerous?

Answer 32

ionising and can penetrate far into the body so cause cell mutation, leading to tissue damage and cancer

Question 33

state the law of reflection

Answer 33

angle of incidence = angle of reflection

Question 34

look at ray diagrams

Answer 34

page 36

Question 35

(Snell's law) refractive index (n) =

Answer 35

sin i / sin r

Question 36

describe the experiment to find refractive index of a glass block

Answer 36

draw around a rectangular block on paper and shine light at an angle trace incident and emergent rays and draw refracted ray (with normal) measure angle i and r use snell's law

Question 37

if the angle i is less than the critical angle then...

Answer 37

most of light passes out and only some is reflected internally

Question 38

if the angle i is equal to the critical angle then...

Answer 38

emerging ray comes out along the surface and quite a lot is reflected internally

Question 39

if the angle i is more than the critical angle then...

Answer 39

no light comes out and all is internally reflected (this is called total internal reflection)

Question 40

sin C =

Answer 40

1 / n

Question 41

How do optical fibres work?

Answer 41

coating inside has a lower refractive index than the central core so that signals passing through hit the core-cladding boundary at angles higher than C so light is always totally internally reflected

Question 42

describe analogue signals

Answer 42

can take any value within its range | the amplitude and frequency can vary continuously

Question 43

describe digital signals

Answer 43

can only take two values (on/off or 1/0) | e.g. you can send data along optical fibres as light pulses

Question 44

what are the advantages of digital over analogue ?

Answer 44

when digital is amplified, interference/noise is ignored, so signal remains high quality quantisation works better with digital can transmit multiple signals at the same time

Question 45

what is interference ?

Answer 45

when 2 or more waves of a similar frequency meet and create one combined signal with a new amplitude

Question 46

what is quantisation ?

Answer 46

rounding multiple values to a smaller set to pack more information into the same amount of space (signal)

Question 47

what is the frequency range humans can hear sounds ?

Answer 47

20 Hz and 20,000 Hz

Question 48

what quickens the speed of sound?

Answer 48

a denser medium as sound is caused by vibrating particles (so travel fastest in solids)

Question 49

sound waves can be...

Answer 49

diffracted, reflected, refracted (and absorbed (curtains and carpets))

Question 50

what is an oscilloscope ?

Answer 50

device that displays sound waves and measures their properties

Question 51

what properties on the oscilloscope effects volume?

Answer 51

amplitude | greater amplitude means more energy and louder sound

Question 52

how does frequency effect sound waves?

Answer 52

changes the pitch, higher frequency (more vibrations) means high - pitched and low frequency means low - pitched