4.4 waves

Question 1

progressive wave

Answer 1

transfers energy without transferring matter

Question 2

define: displacement + unit

Answer 2

distance and direction of a point on the wave from the rest position + m

Question 3

define: amplitude + unit

Answer 3

the max displacement of a point on the wave from the rest position + m

Question 4

define: wavelength + unit

Answer 4

distance from any point to an adjacent point in the same phase + m

Question 5

define: period + unit

Answer 5

time taken for one complete wave to pass a fixed point + s

Question 6

define: frequency + unit

Answer 6

number of waves passing a fixed point per second + Hz

Question 7

define: wave speed + unit

Answer 7

the speed that a peak travels in the direction of the wave + ms-1

Question 8

define: intensity + unit

Answer 8

power per unit area + Wm-2
I = P
A

Question 9

define: path difference

Answer 9

fraction of wavelength by which the oscillations of two waves/points are seperated

Question 10

define: phase difference

Answer 10

fraction of a cycle by whuch their oscillations are seperated measured in radians

Question 11

phase difference equation

Answer 11

= path difference x 2π

Question 12

what type of waves are EM

Answer 12

transverse

Question 13

properties of EM waves

Answer 13

• dont need a medium
• all travel at c

Question 14

order of EM spectrum

Answer 14

radio, micro, infared, visible, uv, x-rays, gamma

Question 15

longitudinal waves + examples

Answer 15

parallel + sound

Question 16

transverse waves + examples

Answer 16

transverse + EM, waves on a string

Question 17

polarisation

Answer 17

if oscillations are restricted to a single plane, the wave is polarised

Question 18

why cant longitudinal waves be polarised

Answer 18

they are oscillations along a line

Question 19

refraction

Answer 19

change of direction when a wave passes at an angle across a boundry between two media

Question 20

why does refraction occur?

Answer 20

waves travel at different speeds in different medias

Question 21

refractive index, n

Answer 21

ratio of the speed of light in a vacuum, to the speed of light in that substance, c

Question 22

refractive index equation:

Answer 22

n = c
v

Question 23

snells law:

Answer 23

n₁ sinθ₁ = n₂ sinθ₂

Question 24

what happens to rays of light travelling from a material with lower n to one with a higher n

Answer 24

they refract towards the normal

Question 25

what happens to rays of light travelling from a material with higher n to one with a lower n

Answer 25

they refract **away** from the normal

Question 26

if the angle of refaction is 90° what is the incidence angle called

Answer 26

critical angle

Question 27

what happens if the angle of incidence is greater than the critical angle

Answer 27

the light will reflect at the boundry - total internal reflection

Question 28

define: black-body

Answer 28

a surface that absorbs all EM radiation

Question 29

define: coherant

Answer 29

waves that have a constant phase difference

Question 30

define: interferance

Answer 30

the superposition of coherent waves

Question 31

antinode

Answer 31

point of max amplitude. formed when progressive waves are in phase

Question 32

node

Answer 32

point of displacement at all times, completely cancel out

Question 33

distance between 2 nodes

Answer 33

1/2 λ

Question 34

what is constructive interference

Answer 34

when 2 waves meet, if their displacements are in the same direction, they combine to give a bigger displacement the points are known as **maxima**

Question 35

what is destructive interference

Answer 35

when 2 waves meet exactly out of phase and cancel out

Question 36

how to observe interference of sound waves

Answer 36

* playing the same sound out of two speakers at the same time * walk across the room parallel to the line between the speakers * quietest point = minima * loudest point = maxima

Question 37

how to observe interference of radio waves

Answer 37

* emitting radiowaves of same frequency from two stationary microwave emitters * move a microwave detector along a line parallel * low readings = minima * high readings = maxima

Question 38

diffraction

Answer 38

spreading of waves when they pass through a gap

Question 39

when does maximum diffraction occur

Answer 39

when the gap is same size as wavelength

Question 40

laser safety

Answer 40

* turn off when not in use * never shine at a person * avoid shining at reflective surfaces * display warning on door

Question 41

how are bright fringes formed

Answer 41

path difference between light from each slit is nλ, interfere constructively

Question 42

how are dark fringes formed

Answer 42

path is (n+1/2)λ, interfere destructively

Question 43

fringe seperation

Answer 43

distance between the centres of two adjacent minimas or maximas

Question 44

wavelength of light equation using seperation:

Answer 44

λ = ax D

Question 45

number of orders of fringes seen for a given wavelength equation:

Answer 45

n = d y