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PHYSICS 160 > Section 4: Waves and Optics > Flashcards

Section 4: Waves and Optics Flashcards

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1
Q

Geometric optics

A

A description of light as ‘rays’ that propagate in straight lines
Only an approximation
Assumes there’s an infinite no of rays originating form each point on an object

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2
Q

Laws of reflection

A

Angle of incidence = angle of reflection

The incident ray, the reflected ray and normal all lie in the same plane. This plane is perpendicular to the surface

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3
Q

What is a ‘normal’

A

An imaginary line perpedicular to a surface

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4
Q

Nature of images in a plane mirror

A

Upright
Same size
Virtual
Equally far behind the mirror as the object is in front

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5
Q

Define virtual image

A

Constructed out of virtual rays traced back behind the mirror to a point of origin

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6
Q

Concave mirror

A

Converging mirror
Caves inwards
Focal point in front of mirror

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7
Q

Convex mirror

A

Diverging mirror
Bulges outwards
Virtual focal point behind mirror

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8
Q

What is ‘n’

A

Index of refraction

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9
Q

Snell’s law of refraction

A

When n2 > n1, light bends toward the normal

When n1 > n2, light behinds away from the normal

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10
Q

Total internal reflection - θc

A

Critical angle, where angle of refraction is 90°

When exceeded, there is no refracted light - all the incident light is reflected back into the medium which it came from

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11
Q

Convex mirror - nature of image

A

Virtual
Erect/upright
Diminished

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12
Q

Concave mirror - nature of image

A

If further out than f:
Real
Inverted
Size depends where image is

If at f, real nor virtual rays converge –> no image (infinity)

If closer than f:
Virtual
Erect
Enlarged

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13
Q

Convex lens - nature of image

A

Depends where the object is

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14
Q

Concave lens - nature of image

A

Virtual
Upright
Reduced
Same side as object

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15
Q

Multiple lenses

A

Overall magnification is the product of the magnification of the 2 lenses

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16
Q

Convex lens - how do rays refract

A

Towards focal point on opposite side of object

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17
Q

Concave lens - how do rays refract

A

Away from focal point on opposite side of object (and so virtual rays towards the focal point on same side of object)

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18
Q

Real image

A

An image that can be projected onto a screen

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19
Q

Virtual images

A

Where rays appear to originate from a common point

Image can’t be projected onto a screen since rays don’t focus

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20
Q

Thin lenses

A

Form images through refraction of light

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21
Q

Converging lens/mirror

A

Convex lens

Concave mirror

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22
Q

Diverging lens/mirror

A

Concave lens

Convex mirror

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23
Q

d(0)

A

Object distance

Always +ve for real objects

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24
Q

d(i)

A

Image distance
Positive for real images
Negative for virtual images

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25
Q

Focal length (f)

A

Focal length for converging mirror/lens is +ve

Focal length for diverging mirror/lens is -ve

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26
Q

M

A

Magnification
+ve for upright image
-ve for inverted image

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27
Q

Double lens - 1st image ends up on other side of second lens

A

Use a -ve sign for d(o.2) in the equation

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28
Q

Wave

A

A disturbance that moves itself and energy but not matter from one place to another in a medium
Particles in the medium vibrate about their original position

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29
Q

Transverse waves

A

Particlesi n the medium move in a direction perpendicular to the direction of travel of the wave

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30
Q

Longitudinal waves

A

Particles in the medium move in a direction parallel to the direction of travel of the wave

31
Q

Most waves in nature are _____

A

Periodic

i.e. they repeat themselves

32
Q

Wavelength (λ)

A

Distance from a point on the wave to the next corresponding point on the wave
Units: m

33
Q

Amplitude (A)

A

Max displacement from the centre line (equilibrium position)

Units: appropriate to type of wave, e.g. m, V, Pa

34
Q

Period (T)

A

Time for one complete vibration

Units: s

35
Q

Frequency (f)

A

No of vibrations per second

Units: Hz

36
Q

Speed (v)

A

Rate of movement (propagation) of a wave

37
Q

Phase

A

Describes at what stage of the cycle as wave is; going up or down, from the reference value

38
Q

In phase

A

Particles in a wave considered to be in phase when they execute the same motion (same stage of their cycle) at the same time

39
Q

180 degrees out of phase

A

Half a cycle out of phase

Execute the exact opp motion at the same time

40
Q

Intensity

A

Power per unit area

41
Q

Decibel (dB) scale

A

Used to compare intensities

42
Q

Intensity and dB

A

Adding 10 dB = multiplying I by 10

3dB is approx 2x intensity

43
Q

Doppler effect

A

The change in the observed f of a wave due to the motion of the wave source relative to the observer

44
Q

Doppler effect - source moving towards observer

A

Increase in f, decrease in wavelength

45
Q

Doppler effect - source moving away from observer

A

Decrease in f, increase in wavelength

46
Q

Principle of superposition

A

The resultant waveform when diff waves meet at the same point in space at the same time is the sum of their individual displacements (heights)

47
Q

Constructive interference

A

2 waves of identical f and A arriving at the same point exactly in phase
Resultant wave has twice the A but same f and wavelength

48
Q

Destructive interference

A

2 waves of identical f and A arriving at the same point exactly out of phase
Resultant wave has zero amplitude

49
Q

Partial destructive interference

A

2 waves of identical f but diff A arriving at the same point exactly out of phase
Resultant wave has same wavelength and f, but its A is the difference of the amplitudes of the individual waves

50
Q

Beats

A

Where 2 waves have slightly diff frequencies and superimpose
Overall amplitude = beat frequency f(B)

51
Q

Natural frequency

A

The f at which an object vibrates when it’s set to vibrate and then left free

52
Q

Forced vibration

A

An object is forced to vibrate at a certain f by constantly applying a periodic force

53
Q

Forced vibration - amplitude

A

Depends on frequency of the forcing

If forced at natural f, the A can grow huge

54
Q

Resonance

A

Tendency of a system to oscillate at larger amplitudes at some f than others
Max amplitude = when system forced to vibrate at its natural frequency = at resonance

55
Q

Avoiding resonance

A

Tuned mass dampers stabilise against violent motion caused by forced vibrations

56
Q

Diffraction

A

The bending of a wave around an obstacle or the edges of an opening

57
Q

Coherent sources

A

Sources that maintain the constant phase difference

58
Q

2 wave sources vibrating in phase

A 
PD = 0 or integer --> constrictive interference
PD = 1/2 wavelength --> destructive interference
59
Q

2 wave sources vibrating out of phase

A 
PD = 1/2 wavelength --> constructive interference
PD = 0 or integer --> destructive interference
60
Q

Light - maxima and minima

A 
Maxima = bright fringes, PD = 0 or integer
Minima = dark fringes, PD = half integer
61
Q

Rayleigh Criterion

A

2-point objects are just resolved when the first dark fringe in the diffraction pattern of one falls directly on the central bright fringe in the diffraction pattern of the other

62
Q

Brester’s law - incident angles other than 0

A

For incident angles other than 0, unpolarised light becomes partially polarised in reflecting from a non-metallic surface

63
Q

Brewster’s law - Brewster angle

A

When unpolarised light is incident on a non-metallic surface at the Brewster angle (θB), the reflected light is 100% polarised in the direction parallel to the surface
The angle between the reflected and refracted rays is 90 degrees

64
Q

(AZ) X

A 
A = nucleon number; no of protons and neutrons
Z = proton number; no of protons
65
Q

Radioactive decay - assumption

A

The probability that any one nucleus out of N nuclei decays in any one second is a constant λ (decay constant)

66
Q

Half-life of a radioactive nuclide

A

The time taken for the no of undecayed nuclei to be reduce to half its original number

67
Q

Nucleus: A = ?

A

A = Z + N (no of protons + no of neutrons)

68
Q

Isotopes

A

Nuclei that contain the same no of protons but diff no of neutrons

69
Q

Strong nuclear force

A

The mutual repulsion of protons tends to push the nucleus apart
The strong nuclear F acts over short ranges and binds the protons and neutrons tgt

70
Q

Nuclear stability

A

As the nuclei gets larger, more neutrons are required for stability

71
Q

Radioactivity

A

Where unstable nuclei can break apart on their own with a predictable probability

72
Q

Alpha decay (α)

A

The nucleus ejects a He nucleus to become a smaller and more stable nucleus

73
Q

Beta decay (β)

A

A neutron is converted to a proton (or vice versa) to become a more stable nucleus
Releases energy - carried away by a neutrino

74
Q

Gamma decay (γ)

A

The nucleus gives off energy in the form of a gamma ray to reach a lower energy state

PHYSICS 160 (5 decks)

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