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Quantum Physics Flashcards

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0
Q

What is the elementary charge?

A

The smallest unit of charge that a particle or an object can have. (Size 1.6x10-19C)

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1
Q

Define electronvolt?

A

The energy transferred when an electron travels through a potential difference of one volt.

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2
Q

Define kinetic energy?

A

Energy of an object due to it’s motion.

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3
Q

Define threshold frequency?

A

The minimum frequency of the electromagnetic radiation that will eject electrons from the surface of a metal.

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4
Q

What particle models do we use to explain macroscopic phenomena?

A

Electricity - flow of electrons (current)
Gases - kinetic theory (pressure etc)
Solids - crystalline materials (mechanical properties)

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5
Q

What wave models are there?

A

Sound
Waves on strings (displacement)
Light (electric and magnetic field sure

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6
Q

What particle models of light are there?

A

A Geiger counter detects the particles alpha and beta. When gamma radiation is put next to a Geiger counter it clicks, meaning it also detects gamma. Gamma is part of the EM spectrum and alpha and beta are particles, but the clicking shows that gamma is acting like a particle and interacting with the counter the same way the alpha and beta particles do.
Also photoelectric effect.

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7
Q

What is a photon?

A

A ‘packet of energy’.

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8
Q

The energy (joules) of an electron = ?

A

Planck constant x frequency
E=hf

h = 6.63x10^-34 Js

J = Js x s^-1

Energy of a photon is directly proportional to frequency.

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9
Q

E(J) =

A

hc/wavelength

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10
Q

How do you convert eV to J?

A

Multiply by 1.6x10^-19

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11
Q

How do you covert J to eV?

A

Divide by 1.6x10-19

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12
Q

Energy change of electron travelling through a p.d. (W) =

A

QV = 1.6x10-19 x voltage

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13
Q

Equation for an electron accelerated from rest? What other particles does this equation account for? When can we not use this equation?

A

eV = 0.5mv^2 note that eV is electron charge multiplied by voltage

Accounts for any type of charged particles (protons and ions etc)

Can not use this equation when the charges particle is accelerated through large voltages to speeds approaching the speed of light because particles mass increases as it approaches speed of light.

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14
Q

Voltage = ?

A

Joules/coulombs(charge)

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15
Q

What factors of LEDs make them ideal for the experiment estimating plancks constant?

A

They conduct in only the forward direction
Requires min voltage (threshold voltage) to be applied before it allows a current.
LEDs of different colours require different threshold voltages before they conduct light.

16
Q

Would a red or blue light need more energy to turn on? Why?

A

Red emits lower energy photons, therefore requires lower threshold voltage to turn on

17
Q

Energy lost by electron to LED = ?

A

Energy of photon

eV = hc/lambda

V is threshold voltage

18
Q

How can we determine h from the LED experiment once we have found V and lambda?

A

A graph of V against 1/lambda can be drawn. The gradient would then equal hc/e.

19
Q

Explain step 1 of an experiment to view the photoelectric effect?

A

1) Get a gold leaf electroscope.
2) Transfer electrons to ES where they stay because it is electrically insulated.
3) Electrons repel each other and distribute themselves evenly throughout structure.
4) Gold leaf lifts because electrons repel each other and it is very light.

20
Q

Step 2?

A

1) Irradiate with UV.

Gold leaf won’t move because each UV photon won’t have enough energy to remove electrons from the steel.

2) Fix a clean zinc plate (no oxide layer) to top of ES.

Gold leaf falls because UV has enough energy per photon to eject an electron from the surface of the metal.
1 photon = 1 electron

21
Q

What are ejected electrons called?

A

Photoelectrons

22
Q

Why, in the photoelectric effect experiment, will zinc lose an electron but steel won’t?

A

Because zinc is more reactive than steel.

23
Q

What is photoelectric emission?

A

The ejection of electrons from the surface of a metal when they are irradiated with photons of high enough energy.

24
Q

What happens if you move the UV lamp closer to the ES? What happens if you place glass in front of it?

A

Falls more rapidly

It won’t fall, glass absorbs UV.

25
Q

Define work function?

A

The minimum energy required by a single electron to escape the metal surface (phi).

26
Q

What happens to the energy from an incident photon arriving at the metal plate?

A

The electron gains the energy and escapes the metal, the rest of the energy is used as KE.

27
Q

Energy of photon (hf) =

Einsteins photoelectric equation

A

Work function + max KE of electron
Phi + KEmax

OR hf = phi + 0.5mv^2

28
Q

How do you work out the threshold frequency?

A

f0 = phi/h

29
Q

Why does a plate under a table lamp get hot?

A

Because the electrons absorb the photons, but can not escape the positive metal ions, so they collide with them causing friction and heat.

30
Q

Page 215

A

Learn observation table

31
Q

What is wave-particle duality of light?

A

The ability of light to act as both a wave and a particle.

Light interacts with matter as a particle (the photon). Evidence is photoelectric effect.

Light travels through space as a wave. Evidence is from diffraction and interference.

32
Q

What is the de Broglie equation?

A

Lambda = h/p

The wavelength here is known as the de Broglie wavelength.

p is momentum (mass x velocity)

33
Q

Explain an experiment to see electron diffraction?

A

Pass a beam of electrons through a graphite film in a vacuum tube. A diffraction pattern will be produced on the phosphor screen.

The electrons are diffracted by the l the spacing between the layers of carbon atoms. They diffract because their de Broglie wavelength is similar to the spacing between the atomic layers.

34
Q

How can you find the wavelength of the electrons being fired as a beam through a vacuum tube and through graphite?

A

Use the equation:

Lamda = dsinθ

Θ is angle at which they are diffracted
d is distance?

35
Q

How can you find the speed at which the electrons are accelerated through the vacuum tube from the anode to the cathode?

A

eV = 0.5mv^2

36
Q

What is wave particle duality of an electron?

A

The ability of an electron to act as both a wave and a particle.

An electron interacts with matter as a particle. Evidence is from Newtonian mechanics.

An electron travels through space as a wave. Evidence from electron diffraction.

Physics (12 decks)

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