M4 Waves - Part 1

Question 1

define wave

Answer 1

periodic disturbance in a material or space
each particle vibrates about a fixed position
energy is transferred outwards from the source of the wave

Question 2

what are progressive waves

Answer 2

an oscillation that travels through matter, transferring energy.
when traveling through a medium, particles move from equilibrium position to a new position.
the displaced particle experiences a restoring force from neighboring particles and returns to its original position.

Question 3

what types of waves are transverse and longitudinal

Answer 3

progressive

Question 4

define transverse waves

Answer 4

the direction of vibration is at 90 degrees to the direction of energy transfer
these have crests and troughs

Question 5

give examples of transverse waves

Answer 5

EM waves
waves on water
s waves in earthquakes

Question 6

define longitudinal wave

Answer 6

the direction of vibration is parallel to the direction of energy transfer. these have compressions and rarefactions

Question 7

give examples of longitudinal waves

Answer 7

sound waves

p waves in earthquakes

Question 8

define mechanical wave

give examples

Answer 8

these waves require a material/medium to transfer through
produced by oscillation of particles in a medium
eg. sound or water

Question 9

define electromagnetic waves

Answer 9

these waves require no medium and so can transfer energy through a vacuum
produced by acceleration of charged particles

Question 10

define amplitude

Answer 10

the maximum displacement of the wave in either the positive or negative direction (from equilibrium position)
unit is m

Question 11

define displacement of a wave

Answer 11

distance of a point from the equilibrium position in a particular direction (vector)
has positive or negative direction

Question 12

define wavelength

Answer 12

Distance between 2 points in phase on adjacent waves

eg. distance between two successive crests

Question 13

define frequency

Answer 13

number of oscillations/vibrations (at a point) per unit time

Question 14

define period

Answer 14

time taken to produce one complete wave

symbol = T

Question 15

define wave speed

Answer 15

distance travelled by a wave per unit time

symbol = v

Question 16

define phase difference

Answer 16

difference between displacements of particles along a wave
a complete wave = 360 degrees or 2π radians
in phase = phase difference of 0
units = degrees or radians

Question 17

derive v = fλ

Answer 17

s = d/t
distance = wavelength
time = period
s = wavelength / period
period = 1/frequency
s = wavelength / 1 / frequency 
s = wavelength X frequency
s = v
v = f X λ

Question 18

classify the following waves:

a) sound
b) light
c) water
d) x-rays
e) microwaves

Answer 18

a) sound = longitudinal and mechanical
b) light = transverse and electromagnetic
c) water = transverse, sometimes longitudinal and mechanical
d) x-rays = transverse and electromagnetic
e) microwaves = transverse and electromagnetic

Question 19

what are all the basic wave properties of EM waves

Answer 19

reflection
refraction
diffraction
polarisation
interference
energy transference

Question 20

what is the speed of EM waves

Answer 20

3 X 10^8 ms^-1

Question 21

which of radio waves or gamma rays has the longest wavelength?

Answer 21

radio

Question 22

what is the wavelength of radio waves

Answer 22

10^-1 - 10^6

Question 23

what is the wavelength of microwaves

Answer 23

10^-3 - 10^-1

Question 24

what is the wavelength of infrared waves

Answer 24

7 X 10^-7 - 10^-3

Question 25

what is the wavelength of visible light waves

Answer 25

4 X 10^-7 - 7 X 10^-7

Question 26

what is the wavelength of ultraviolet waves

Answer 26

10^-8 - 4 X 10^-7

Question 27

what is the wavelength of x-rays

Answer 27

10^-13 - 10^-8

Question 28

what is the wavelength of gamma rays

Answer 28

10^-16 - 10^-10

Question 29

on a EM wave, how do the magnetic and electric field relate

Answer 29

they are perpendicular to each other

Question 30

radio waves what can it penetrate through? what are the uses?

Answer 30

pass through matter radio transmissions

Question 31

microwaves what can it penetrate through? what are the uses?

Answer 31

mostly pass through matter but causes some heating

Question 32

infrared what can it penetrate through? what are the uses?

Answer 32

absorbed by matter, causing it to heat up heat detectors, night vision cameras, remote controls and optical fibres

Question 33

visible light what can it penetrate through? what are the uses?

Answer 33

absorbed by matter, causing heating human sight, optical fibres

Question 34

ultraviolet what can it penetrate through? what are the uses?

Answer 34

absorbed by matter, cause some ionisation sunbeds, security marks that show up under UV

Question 35

x-rays what can it penetrate through? what are the uses?

Answer 35

mostly pass through matter, cause ionisation as they pass see the damage to bones and teeth, airport security scanners, kill cancer cells

Question 36

gamma rays what can it penetrate through? what are the uses?

Answer 36

mostly pass through matter, cause ionisation as they pass irradiation of food, sterilisation of medical instruments, kill cancer cells

Question 37

what waves does polarisation effect

Answer 37

transverse waves

Question 38

describe an experiment to demonstrate the polarisation of microwaves

Answer 38

Place microwave transmitter and receiver facing each other Rotate one of them through 90 degrees about axis Observe signal fall to zero from initial high value on meter monitoring output of the receiver Use 2 polarising filters and rotate from parallel to crossed

Question 39

how is polarisation used in microwave ovens

Answer 39

unpolarised rays of microwaves are prevented from leaving the microwave by a fine metal grid covering the door this grid absorbs both horizontal and vertical oscillations of the microwaves

Question 40

draw a diagram which represent unpolarised light

Answer 40

a line with dots with arrows going up and down

Question 41

draw a diagram to show vibrations of E-field in unpolarised light

Answer 41

a dot with arrows going out in lots of directions

Question 42

draw a diagram of how a polaroid is used when the first one to the light is verticle and the next one is horizontal

Answer 42

unpolarised light goes in the vertical polaroid and keeps going through but is stopped by the horizontal polaroid the vertical polaroid is called the polariser the horizontal polaroid is called the analyser

Question 43

draw a diagram to show polarised light by relfection

Answer 43

look it up | pg 10 of 1st waves booklet

Question 44

what is plane polarised light

Answer 44

when all of the waves are in the same plane applies to transverse waves

Question 45

why is light from a candle unpolarised

Answer 45

every wave is aligned in a random and different plane

Question 46

what is reflection | what is the law of reflection

Answer 46

all waves reflect off a surface for a plane surface , the angle of reflection = angle of incidence normal is drawn perpendicular to the surface

Question 47

what is refraction

Answer 47

if waves goes through a boundary, their speed and wavelength changes if they are incident at a non-zero angle to the boundary then they will change direction

Question 48

what is diffraction | when does max diffraction happen

Answer 48

waves that pass through a gap or around an obstacle will spread out maximum diffraction happens when the gap is similar in size to the wavelength of the wave

Question 49

what is the intensity of a progressive wave

Answer 49

the power passing through a surface per unit area | unit is Wm^-2

Question 50

how does intensity and distance relate

Answer 50

intensity decreases with distance I is directly proportional to 1/r^2 when they give a distance in a question it means the radius

Question 51

how does intensity and amplitude relate

Answer 51

decreasing amplitude means reduce in average oscillating speed of particles I is directly proportional to A^2 eg. doubling the amplitude means 4X the intensity

Question 52

what are the proportionalities you need to know for intensity

Answer 52

I directly proportional 1/r^2 I directly proportional A^2

Question 53

if the distance from earth to the sun is 1.5 X 10^11 m and the intensity is 1400 Wm^-2 then what is the power

Answer 53

``` I = P / A P = AI A = 4πr^2 = (4π(1.5 X 10^11)^2) X 1400 = 4X10^26 W ```