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Physics > Quantum phenomena > Flashcards

Quantum phenomena Flashcards

1
Q

Describe the gold leaf electroscope parts

A

A metal plate attached to a right metal pole. Attached to this is a piece of gold foil.

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2
Q

What causes the flexible gold foil to repel away from the metal pole?

A

Adding extra electrons
-This makes it negatively charged
-So both the pole and foil are negatively charged
-So it repels away

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3
Q

What happens when light of a certain frequency is shone into the metal plate?

A

The gold foil falls back down

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4
Q

Why does the gold foil fall back down when light of a certain frequency is shone on it?

A

-The light causes electrons to be released from the metal
-So apparatus becomes negatively charged
-So the repulsion weakens

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5
Q

What happens if you charge the gold leaf electroscope experiment positively?

A

If the metal is positively charged then the negative electrons are attracted back to the plate so it’s harder for them to escape.

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6
Q

What did wave theory predict about frequency?

A

Wave theory predicted that any frequency of light should cause the photoelectric effect

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7
Q

How does frequency actually effect the photoelectric effect?

A

Only above a certain threshold frequency electrons are emitted

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8
Q

What did wave theory predict about light intensity?

A

Wave theory predicted increasing light intensity would increase the energy of electrons emitted

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9
Q

How does light intensity actually effect the photoelectric effect?

A

As long as you’re in the threshold frequency increasing intensity increases the amount of electrons. Energy stays the same.

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10
Q

What does the existence of threshold frequency show?

A

Energy must be delivered in packets and must be proportional to the frequency of the wave.
All delivered in one go as electrons can’t store energy

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11
Q

What is the photoelectric effect equation?

A

hf=ϕ+Ekmax

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12
Q

How does a vacuum photocell work?

A

As you increase the voltage the eye becomes more negative and the smile becomes more positive
-So it’s harder for electrons to escape

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13
Q

Vacuum photocell equation

A

eVs=Ekmax

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14
Q

What happens if you heat up (excite) a gas?

A

You can cause it to glow.

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15
Q

How can you heat up (excite) a gas?

A

You can heat them up by passing a very high current through them.
The high current is made of fast moving electrons.

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16
Q

How do you see the multiple photons in a glowing gas?

A

Splitting light using a prism / diffraction grating

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17
Q

What happens if you de excite (cool) a gas and pass white light through?

A

Certain photons are blocked

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18
Q

Energy level rules

A

-Electrons can move up/down
-If they absorb energy they move up
-If they emit energy they move down
-Electrons cannot exist inbetween levels

19
Q

What is energy level 1

A

The ground state
Electrons are most stable here
Electrons have the least energy

20
Q

What is the ionisation level?

A

When electron has completely left the atom

21
Q

How can electrons gain energy?

A

Absorbing a photon or get hit by another electron

22
Q

What allows an electron to absorb a photon?

A

An electron can only absorb a photon of it gives it exactly the right amount of energy to move up 1 or more whole levels

23
Q

Ionisation energy

A

The minimum energy needed to remove an electron from the atom from the ground state

24
Q

Explain why an electroscope won’t show the photoelectric effect if it’s positively charged

A

Electrons would be attracted back by the positive charge
So the gold foil won’t stop repelling

25
Q

What is the threshold frequency evidence for?

A

Light can exist in discrete energy packets called photons

As the electrons need all energy to be transferred at the same time to be emitted

26
Q

Explain why increasing the intensity of the light increases the amount of photoelectrons emitted?

A

Increasing the intensity increases the number of photons striking the plate per second.
For each photon an electron is emitted.
So the number of photoelectrons released per second increases.

27
Q

Define the work function of a metal

A

The minimum energy needed for an electron to be released from the surface of the metal

28
Q

Define the threshold frequency

A

The minimum frequency needed for an electron to be released from the surface

29
Q

When electrons are excited to a higher energy level explain why different frequencies are possible

A

Electrons cascade rather than going straight to the ground state

30
Q

Describe how the concept of energy levels is useful in the explanation of line spectra

A

Only certain energy changes allowed

A line corresponds to a transition between levels

Each transition corresponds to a definite wavelength

31
Q

What happens in an atom when line spectra are produced?

A

Electrons move up and down energy levels
By emitting or absorbing a definite photon energy

32
Q

Explain what is meant by the duality of electrons

A

Electrons sometimes behave like particles and sometimes behave like waves

33
Q

Evidence that demonstrates electrons have particle properties

A

Deflection in E field

34
Q

State what is meant by the wave particle duality of electromagnetic radiation

A

EM radiation sometimes behaves like waves and sometimes behaves like particles

35
Q

Explain why the kinetic energy of emitted electrons has a maximum value

A

hf is energy received from photons

Energy required to remove the electron varies

So KE of electrons will vary

36
Q

Evidence for light behaving like particles

A

Photoelectric effect
Existence of threshold frequency

37
Q

Evidence for light behaving like waves

A

Diffraction
Interference pattern seen

38
Q

Evidence for electrons behaving like particles

A

Deflection in magnetic field

Curved track of electron

39
Q

Evidence for electrons behaving like waves

A

Electron diffraction

Interference pattern seen

40
Q

How does the wavelength relate to the diffraction gap

A

Same order of magnitude

41
Q

What does the mercury electron emit when it returns to ground state

A

Ultraviolet photon

42
Q

Why must a photon have an exact amount of energy whereas a free electron only needs a minimum amount of kinetic energy

A

For a transition an exact amount of energy is needed

All of the photons energy is absorbed (1:1 interaction)

Electrons can transfer part of their energy and have a lower speed

43
Q

How does the phosphorus coating work in fluorescent tubes?

A

-UV photons excite electrons in ground state of coating to higher energy level
-Electrons cascade back down releasing lower energy photons

44
Q

How do fluorescent lamps work?

A

-High pd accelerates electrons across tube
-These electrons collide with electrons in the ground state of the mercury
-The free electrons gain energy and move to higher levels
-When the move back down UV photons released
-Phosphorous coating turns then into visible light photons

Physics (7 decks)

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