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Physics AS 1 > Chapter 17- Particle Nature Of Light > Flashcards

Chapter 17- Particle Nature Of Light Flashcards

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1
Q

What is newton’s corpuscular theory?

A

He thought of light as being made up of corpuscles (or tiny particles)

He imagined the particles to bounce of the surfaces explaining reflection

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2
Q

What was Huygen’s wave theory?

A

Light consisted of waves like ripples spreading out like a stone dropped in water

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3
Q

Difference between Huygen’s or newton’s theories?

A

The differences in our if water or glass and then in air which medium means light has the fastest speed

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4
Q

Intensity def

A

The power per unit area

Has units W m^-2

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5
Q

Another way of saying intensity

A

Radiation flux density

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6
Q

Intensity eq

A

Intensity = power/area

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7
Q

If we are a distance r from point source of radiation, what will happen to the radiation?

A

It will spread out in all directions over a sphere of surface area 4pie r^2

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8
Q

The photoelectric effect can be demonstrated by what means?

A

A negatively charged zinc plate and a UV lamp

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9
Q

What happens in photoelectric effect?

A

The freshly cleaned zinc plate is given a negative charge
Under visible light photoelectrons are discharged at a very low rate
But under slight UV light they are discharged immediately

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10
Q

If zinc plate is positively charged what happens with the photoelectric effect?

A

Nothing at all

As any photoelectrons transmitted would be attracted to the plate

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11
Q

What is the photoelectric effect?

A

When energy from the light is given to the electrons causing their emission from the substance

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12
Q

If ONE photon had enough energy then…

A

It will release ONE photoelectron

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13
Q

What is a quanta now called

A

A photon

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14
Q

What is a quanta formed from

A

Discrete bundles of energy

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15
Q

Instead of energy from the light being gradually absorbed by the electrons near the surface….

A

Einstein reasoned that

The electron would be emitted only if a single quantum of the light had enough energy for the electron to escape

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16
Q

What is Einsteins theory called?

A

Quantum theory

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17
Q

Why can UV discharge a photoelectron and visible light can’t?

A

Because UV has a higher frequency than visible light

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18
Q

The intensity of a light source depends on… (2)

A

The number of quanta

The energy associated with each quantum

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19
Q

Electron volt def

A

The work done on (or gained by) an electron when it moves through a potential difference of 1 volt

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20
Q

Electron volt unit

A

eV

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21
Q

1 electron volt has how many joules of energy?

A

1.6 x10 ^-19 J

22
Q

What is the bare minimum energy needed to liberate an electron from the surface called?

A

The work function

Symbol= o with line through it

23
Q

If a photon of energy hf has more than the work function what does it go into

A

Kinetic energy

24
Q

maximum kinetic energy an electron can have eq

A

hf= 🚫+ 1/2 mvmax^2

25
Q

What is Einsteins photoelectric eq

A

hf= 🚫+ 1/2mvmax^2

26
Q

Electrons are emitted with a range of kinetic energies up to the maximum because…

A

Because electrons inside the metal will need more than the work function to escape

27
Q

There will be no photoelectric emission unless…

A

hf>🚫

28
Q

Threshold frequency

A

Frequency just large enough to liberate electrons fo

So 🚫=hfo

29
Q

What is a phototube?

A

Name given to a type of photocell that generates photoelectrons when light falls on a specifically coated metal cathode

30
Q

What is a photovoltaic photocell?

A

In which an emf is generated by the presence of light across the boundary of two semiconducting materials, the photoconductive cells, or LDRs

31
Q

Ground state def

A

The state an electron is in when it is at its lowest possible energy level

32
Q

Ionisation energy def

A

The energy that must be supplied for an electron in the lowest energy level to just escape from the atom

33
Q

Quantum DEFINITION

A

A fixed or discrete amount of energy

34
Q

Emission spectrum def

A

Of a chemical element or compound, is the spectrum of frequencies of electromagnetic radiation emitted when the electrons in an atom make a transition from a high energy state to a lower-energy state

35
Q

When an electron drops from energy level E2 to a level E1 eq

A

hf= E2 - E1

36
Q

Applications of quantum emission (2)

A
  • radar (radio detection and ranging)

* laser

37
Q

What happens in an absorption spectrum?

A

Radiation is absorbed by a substance at frequencies that match the energy difference between two quantum states of electrons in an atom or molecule of the substance

38
Q

What is wave-particle duality?

A

The concept describing the fact that light behaves like waves and also like a particle

39
Q

What is Broglie’s wave-particle duality eq?

A

Wavelength= h/p (momentum)

40
Q

What is the complementarity principle?

A

Says that sometimes electrons have the properties of particles and sometimes the properties of waves, but never both together

41
Q

What is plank’s constant

A

6.63 x10 ^-34

42
Q

Energy eq

A

E= hf

43
Q

Kinetic energy max eq

A

KE= hf- 🚫o

44
Q

Stopping potential def

A

Point of frequency at which no flow is created as all photoelectrons released are then attracted back to the original cathode as they run out of energy

45
Q

Stopping potential eq

A

Vs x charge = E

Therefore..
qVs= hf- 🚫o = KE max

46
Q

Charge of an electron

A

1.6 x10 ^-19

47
Q

Alternative eq to

KE= hf- 🚫

A

KE= hc/wavelength - 🚫

48
Q

Electric fields cause

A

Voltages

49
Q

A photon can be emitted in

A

Any direction

Fewer photons therefore come back towards you (intensity decreased)

50
Q

You can tell the type of elements something is made up from by…

A

The absorption spectrum

51
Q

What type of emission when dropping down energy states

A

Spontaneous emission

52
Q

Mass of an electron

A

9.1x10 ^-31

Physics AS 1 (10 decks)

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