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physics > particles and waves (part 2) > Flashcards

particles and waves (part 2) Flashcards

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1
Q

equation for energy of a photon

A

E=hf

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2
Q

what is wave-particle duality?

A

light being observed as a wave or particle, depending on how we observe it

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3
Q

how can electrons escape an atom?

A

by absorbing the minimum energy required, Eo (work function), and minimum frequency, fo (threshold frequency), from a photon of light

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4
Q

how can we allow for more electrons to be released?

A

increasing irradiance of light source, as long as its above threshold frequency

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5
Q

what is the work function?

A

the minimum energy required to release an electron from a surface

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6
Q

what is the threshold frequency?

A

the minimum frequency of the photon of light that allows the electron to be released from an atom

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7
Q

work function equation

A

Eo=hfo

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8
Q

what is condition is required for the electron to have kinetic energy?

A

energy of photon must be greater than the work function- this extra energy would appear as kinetic energy

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9
Q

equation for kinetic energy of an electron

A

Ek= E-Eo

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10
Q

what is the photoelectric effect?

A

when light of a specific frequency falls on a metal plate and ejects electrons from its surface

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11
Q

what evidence is there for the particle nature of light?

A

each photon removes one electron from surface

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12
Q

what evidence is there for light being a wave?

A

phenomenon of interference of light

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13
Q

when is interference observed?

A

when two waves with the same frequency and wavelength overlap

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14
Q

what is the effect of interference dependant on?

A

whether the waves are in phase or out of phase

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15
Q

what is constructive interference and when does it occur?

A

when two waves of equal amplitude meet in phase and combine to give a wave of twice the amplitude

when a wave crests coincide or wave troughs coincide

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16
Q

3 things coherent waves share

A

same frequency, wavelength, and phase

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17
Q

what is destructive interference and when does it occur?

A

when two waves of equal amplitude meet out of phase and combine to give a wave of zero amplitude

when a wave crest coincides with a wave trough

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18
Q

what part of a water wave displays constructive interference?

A

bold lines moving outward from ripple

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19
Q

what part of a water wave displays destructive interference?

A

faded gaps in between each section of lines

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20
Q

example of the interference of light

A

youngs double slit experiment

monochromatic light shone through single slit producing a source of coherent waves

pass through a double slit to produce two coherent sources of waves

interference fringes produced on screen consisting of bands of bright light (constructive interference) and dark bands (destructive interference)

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21
Q

what happens as frequency increases?

A

wavelength decreases

22
Q

maxima path difference equation

A

pd= nλ

23
Q

minima path difference equation

A

pd= (n+1/2)λ

24
Q

how does a grating work?

A

made up of many slits placed very close together

light passes through and depending on path difference to screen, a particular interference pattern is produced

25
Q

equation for wavelength of laser and fringe seperation

A

mλ= dsinθ

26
Q

equation for lines between slits

A

d= 1/lines per mm

27
Q

notation for nm

A

10^-9

28
Q

why is central maximum always white?

A

path difference to it is zero for all wavelengths or colours of light

these superimpose on each other to produce white light

29
Q

what colour is always closest to central maxima

A

violet

30
Q

what is the refractive index?

A

the refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium

(constant produced when plotting the sine of the angle of incidence against the sine of the angle of refraction)

31
Q

refractive index formula

A

n= sinθ1/sinθ2

32
Q

equation for snells law (full refractive index equation)

A

n2sinθ2 = n1sinθ1

33
Q

what does the refractive index measure?

A

the effect a medium has on light

34
Q

the greater the refractive index, the…

A

greater the change in speed and direction

35
Q

equating snells law, velocity, and wavelength

A

n2/n1 = sinθ1/sinθ2 = v1/v2 = λ1/λ2

36
Q

equating velocity and wavelength

A

v1/λ1 = v2/λ2

37
Q

what is irradiance?

A

the power per unit area

(i.e. watts per square metres)

38
Q

irradiance formula

A

I= P/A

39
Q

irradiance units

A

wm^-2

40
Q

how to show the relationship between irradiance and distance

A

light meter measures light levels at a range of distances from the light bulb in an otherwise completely dark room

41
Q

what does a graph of irradiance against the inverse of squared distance prove?

A

irradiance is directly proportional to the inverse of the squared distance

42
Q

levels of irradiance with changing distance from source formula

A

i1d1² = i2d2²

(i = k/d² )

(D(i1d1² = k))

43
Q

when can an electron move to a higher energy level?

A

if the electron gains energy but only at discrete energies

44
Q

difference between energy levels formula

A

E2-E1= hf

45
Q

what happens when an electron loses energy and moves to a lower level?

A

emits a photon

46
Q

what is seen in the line spectrum for sodium light?

A

two yellow lines that are close together, which are especially bright

due to there being a lot of electrons making that energy jump, not because it is a large energy jump

47
Q

how can electrons move up energy levels?

A

absorb photons of light that contain the required amount of energy and a particular frequency since E= hf

48
Q

what happens when many electrons are making the same upward jump of energy levels?

A

a reduction in the number of photons with that energy level and of a particular frequency

49
Q

why are there missing lines in the emission spectrum of the sun?

A

gases present in the outer part of the sun absorb photons of particular frequencies

absorption lines produced as a result correspond to the emission lines of particular elements- allowing identification of elements present in gas

50
Q

what is found when passing white light through an element in gaseous form?

A

results in dark bands appearing in the spectrum of white light

two dark lines found where the bright yellow line emission spectrum are found

physics (4 decks)

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