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physics > 4.4 waves > Flashcards

4.4 waves Flashcards

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1
Q

progressive wave

A

transfers energy without transferring matter

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2
Q

define: displacement + unit

A

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

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3
Q

define: amplitude + unit

A

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

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4
Q

define: wavelength + unit

A

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

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5
Q

define: period + unit

A

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

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6
Q

define: frequency + unit

A

number of waves passing a fixed point per second + Hz

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7
Q

define: wave speed + unit

A

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

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8
Q

define: intensity + unit

A

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

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9
Q

define: path difference

A

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

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10
Q

define: phase difference

A

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

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11
Q

phase difference equation

A

= path difference x 2π

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12
Q

what type of waves are EM

A

transverse

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13
Q

properties of EM waves

A
  • dont need a medium
  • all travel at c
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14
Q

order of EM spectrum

A

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

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15
Q

longitudinal waves + examples

A

parallel + sound

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16
Q

transverse waves + examples

A

transverse + EM, waves on a string

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17
Q

polarisation

A

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

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18
Q

why cant longitudinal waves be polarised

A

they are oscillations along a line

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19
Q

refraction

A

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

20
Q

why does refraction occur?

A

waves travel at different speeds in different medias

21
Q

refractive index, n

A

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

22
Q

refractive index equation:

A

n = c
v

23
Q

snells law:

A

n₁ sinθ₁ = n₂ sinθ₂

24
Q

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

A

they refract towards the normal

25
Q

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

A

they refract away from the normal

26
Q

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

A

critical angle

27
Q

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

A

the light will reflect at the boundry - total internal reflection

28
Q

define: black-body

A

a surface that absorbs all EM radiation

29
Q

define: coherant

A

waves that have a constant phase difference

30
Q

define: interferance

A

the superposition of coherent waves

31
Q

antinode

A

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

32
Q

node

A

point of displacement at all times, completely cancel out

33
Q

distance between 2 nodes

A

1/2 λ

34
Q

what is constructive interference

A

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

35
Q

what is destructive interference

A

when 2 waves meet exactly out of phase and cancel out

36
Q

how to observe interference of sound waves

A
  • 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
37
Q

how to observe interference of radio waves

A
  • emitting radiowaves of same frequency from two stationary microwave emitters
  • move a microwave detector along a line parallel
  • low readings = minima
  • high readings = maxima
38
Q

diffraction

A

spreading of waves when they pass through a gap

39
Q

when does maximum diffraction occur

A

when the gap is same size as wavelength

40
Q

laser safety

A
  • turn off when not in use
  • never shine at a person
  • avoid shining at reflective surfaces
  • display warning on door
41
Q

how are bright fringes formed

A

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

42
Q

how are dark fringes formed

A

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

43
Q

fringe seperation

A

distance between the centres of two adjacent minimas or maximas

44
Q

wavelength of light equation using seperation:

A

λ = ax
D

45
Q

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

A

n = d
y

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