Section 3 - Waves

Question 1

wavelength λ

Answer 1

distance from one peak to the next

Question 2

frequency (f)

Answer 2

how many complete waves there are per s (passing a certain point)
measured in Hz (1Hz = 1 wave per second)

Question 3

amplitude is

Answer 3

height of wave (from rest to crest)

Question 4

speed (v)

Answer 4

how fast wave goes

Question 5

period (T)

Answer 5

time in s it takes for one complete wave to pass a point

Question 6

frequency formula

Answer 6

f = 1/T

Question 7

wave speed (m/s) formula

Answer 7

frequency (hz) x wavelength (m)
v = f x λ

Question 8

transverse waves

Answer 8

the vibrations are at 90º to the direction energy is transferred by the wave
/\/\/\/\/\/\/\
examples:
- light and EM waves
- slinky spring
- waves on strings
- ripples in water

Question 9

longitudinal waves

Answer 9

vibrations are along same direction as the wave transfers energy
lll l l l ll l l l l ll llll l l ll l l lll lllllll ll l l l l ll l l l ll
compressions and rarefactions
exampkes:
- sound and ultrasound
- shock waves
slinzy spring when you push end

Question 10

what waves transfer

Answer 10

• all transfer energy in direction they are travelling
• can also transfer information

Question 11

wavefronts

Answer 11

imaginary planes cutting across all waves connecting points on adjacent waves vibrating together

distance between wavefronts is one wavelength

when talking ab waves aproching obstace multiple waves in same direction are referd to as wavelengths

Question 12

doppler effect

Answer 12

waves produced by a source which is moving will have different wavelength than if source were stationary

frequency of a wave from source moving towards you will be higher and wavelength will be shorter than wave froduced by source and viceversa

Question 13

EM waves

Answer 13

have different properties and grouped depending on wavelength
transverse

Radio (least frequency and largest wavelength)
Micro-waves
infrared
visible light
uv
xrays
gamma

Question 14

uses of radio waves

Answer 14

1) communication
- long and short wave

• missing details

Question 15

uses of microwaves

Answer 15

satellite communication and heating food
*

Question 16

uses of infrared radiation

Answer 16

heating and monitor temperature *

Question 17

EM Light

Answer 17

colours depend on wavelength (red, organge yellow green blue indigo violet)

travel through optic fibres (carry data long distances as pulses of light)

pulse of light enters at certain angle and is refracted continiously until it emerges at other end
*

Question 18

visible light uses

Answer 18

optic cables - (telephone internet and mediacal)
photography
*

Question 19

uv uses

Answer 19

used in florescent light
*

Question 20

xrays uses

Answer 20

viewing internal structures

*

Question 21

gamma uses

Answer 21

steralising medical equipement
streilising food (and keeping it fresh)

Question 22

how can em be harmful

Answer 22

most em pass thrpugh tissues without being absorbed, but they can also
1) cause heating of cells (micro-waves)
2) cause cancerous mutations in living cells (gamma)

higher freq = more energy = more dangerous

Question 23

dangers of microwaves

Answer 23

internal heating - microwave ovens must be shielded to prevent this *

Question 24

infrared dangers

Answer 24

internal heating that can cause skin burns
- protect yourself using insulating materials*

Question 25

UV dangers

Answer 25

damage surface cells and cause blindness
cell mutation/destruction
(ionising - knock electrons off magnets)

sunscreen with uv filters
*

Question 26

gamma dangers

Answer 26

cell mutation / desturction (also ionising)
leads to tissue damage or cancer

radioactive sources should be kept in lead-lined boxes and exposure as short as possible
*

Question 27

diffuse reflection

Answer 27

when light reflects from an uneven surface the light reflects off at different angles causing a diffuse reflection

Question 28

clear reflection

Answer 28

when light reflects from an even surface then it is all reflected in same angle and you get a clear reflection

Question 29

law of reflection

Answer 29

angle of incidence = angle of reflection

Question 30

the normal

Answer 30

the perpendicular imaginary line to surface at point of incidence (usually shown as dotted line)

Question 31

virtual images

Answer 31

form when light rays bouncing off an object onto a mirror are diverging so light from object apperars to be comming from a completely different place

Question 32

how are waves refracted

Answer 32

travel at different speeds through substances with different densities (em travel slower in denser media, while sound travels faster)

wave hits boundary face on - slows down but carries on in the same direction
wave meets boundary at an angle - top part hits have first and slows down only later followed by bottom part, causing a wave to change direction - be refracted

Question 33

drawing refracted wave

Answer 33

1) draw boundary & normal
2) incident ray that meets normal at boundary
3) angle between ray and normal is angle of incidence
4) now draw refracted ray.
2 material denser = bends towards normal
angle of refraction smaller than angle of incidence

Question 34

refractive index

Answer 34

tells you how fast light travells through a material

n = speed of light in a vacuum (c) / speed of light in material (v)

n = c/v

light slows down = high n

Question 35

snells law

Answer 35

n = sin i (incidence) / sin r (refr)i

Question 36

critical angle

Answer 36

r = 90º. light is refracted right along boundary

Question 37

snells law to find critical angles

Answer 37

sin C = 1/n

higher n means lower C

Question 38

optical fibres

Answer 38

made of plastic/glass consist of central core surrounded by cladding with a lower refractive index
core of fibre is so narrow that light signals always hit boundary at angles higher than C so light is always totaly internally reflected and only stops working if bent too sharply

Question 39

Prisims

Answer 39

ray of light travels into one prism where it is totally internally reflected by 90º
then travells to another prism and is again totally internally reflected by 90º
ray is now travelling parallel to initial path but at different height

Question 40

Sound as a wave

Answer 40

will be reflected by hard surfaces (carpets and curtains absorb sound)
refract in diffeent media - denser means they speed up but change in direction is hard to spot