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Physics A/S Wjec Unit 2 > Unit 2.7: Photons > Flashcards

Unit 2.7: Photons Flashcards

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1
Q

Other than behaving as waves, how else can light behave?

A

As a stream of particles

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2
Q

Energy in a light wave is not a continuous stream but rather is quantized into what?

A

Little bundles of energy known as QUANTA or PHOTONS

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3
Q

What did concept did Max Planck introduce?

A

That energy of a photon is a fixed amount
Concept of quantisation of energy

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4
Q

What did Einstein conclude from the quantisation of energy?

A

That the energy of a photon is proportional to the frequency of radiation

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5
Q

What is a photon?

A

A discrete packet of energy

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6
Q

What is the equation for the energy of a photon?

A

Ephot=hf or E=hc/λ

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7
Q

What is one electron volt(eV)?

A

One electronvolt is the energy of an electron accelerated by a potential difference of 1 Volt

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8
Q

What unit is used to describe the energy of a single photon?

A

Joule

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9
Q

What is 1eV in Joules

A

1eV=1.6x10^-19J

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10
Q

What is the typical wavelength for Gamma waves?

A

10^-12m

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11
Q

What is the typical wavelength for X-ray waves?

A

10^-10m

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12
Q

What is the typical wavelength for UV waves?

A

10^-7 or 10^-8

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13
Q

What is the typical wavelength for visible waves?

A

4x10^-7m to 7x10^-7m
4=Blue
7=Red

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14
Q

What is the typical wavelength for infrared waves?

A

10^-5m

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15
Q

What is the typical wavelength for Microwaves?

A

10^-2

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16
Q

What is the typical wavelength for radio waves?

A

10^2

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17
Q

What is the typical photon energy for Gamma waves?

A

10^6 eV

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18
Q

What is the typical photon energy for an X-ray wave?

A

10^4 eV

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19
Q

What is the typical photon energy for UV?

A

10^1 eV

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20
Q

What is the typical photon energy for visible light?

A

3.1eV to 1.8eV
blue red

21
Q

What is the typical photon energy for infrared waves?

A

10^-1eV

22
Q

What is the typical photon energy for microwaves?

A

10^-4eV

23
Q

What is the typical photon energy for radio waves?

A

10^-8eV

24
Q

What is the photoelectric effect?

A

When light or UV radiation of short enough wavelength falls on a surface, electrons are emitted from the surface

25
Q

What is work function(Φ)?

A

The work function is the minimum energy required to remove an electrons from the surface

26
Q

What are the units for Work function?

A

Joules or electronvolts

27
Q

What is threshold frequency (f0)?

A

The minimum frequency of a photon that will cause the emission of an electron from a particular metal surface

28
Q

What happens when EM radiation of enough energy strikes the cathode surface?

A

Electrons are ejected

29
Q

What are photoelectrons?

A

Ejected electrons from the surface of a cathode

30
Q

During the photoelectric effect experiment, where do the photoelectrons travel and what does this create in the circuit?

A

The photoelectrons travel across to the anode and a current flows in the circuit

31
Q

During the photoelectric effect experiment, how is current read?

A

Using an ammeter

32
Q

During the photoelectric effect experiment, the p.d is increased in the circuit it until what happens?

A

The photoelectrons are being repelled from the anode and at certain p.d the electrons won’t have enough energy to reach the anode

33
Q

The cathode and anode have to be in what during the photoelectric effect experiment

A

They must be in a vacuum otherwise the ejected electrons could collide with molecules in the air

34
Q

State the steps for the photoelectric experiment

A
  1. Shine the light on cathode
  2. Adjust p.d until micro-ammeter shows 0 current
  3. Read voltmeter
  4. Plot a graph, current against p.d
35
Q

If the intensity of light increases, what happens to the number of photons of light

A

They increase

36
Q

Ek max=Evstop

A
37
Q

State Einstein’s photoelectric equation

A

Ekmax=hf-Φ

38
Q

If the energy of a photon is just enough to cause an electron to be ejected then te photoelectron will have no Ek. State the photoelectric equation with no Ek.

A

hf0=Φ

39
Q

Ekmax=hf0-Φ & y=mx+c predicts what on a photoelectric graph

A

That Ekmax against f will be a straight line

40
Q

How do you find threshold frequency on a photoelectric graph?

A

Where the line crosses the x axis

41
Q

What idea did Niels Bohr develop in 1913

A

-Energy in atoms was quantised and the the electrons existed in specific energy levels

42
Q

According to Niels Bohr, when can electrons move between energy levels?

A

When they are given the correct quantity of energy usually in the form of a photon

43
Q

If an electron want to move up an energy level, it must absorb what particle?

A

Photon

44
Q

If an electrons wants to move down an energy level is must emit what particle?

A

Photon

45
Q

What is ionisation energy?

A

The minimum energy required to remove an electron from the atom in its ground state

46
Q

How does an absorption spectra form in terms of electrons?

A

When light passes through clouds of gas in the star’s atmosphere and certain wavelengths are absorbed as electrons are promoted to higher energy levels

47
Q

What is the emission spectrum?

A

Electrons collide with atoms in the gas and cause electrons to be promoted to higher energy levels. We get coloured lines.

48
Q

What is electron diffraction?

A

When a beam of electrons is accelerated through a thin polycrystalline graphite film in an evacuated chamber with a fluorescent screen to see where the electrons come out the other side. This creates a diffraction grating

Physics A/S Wjec Unit 2 (8 decks)

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