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A-level Physics > Module 4.5 - Quantum Physics > Flashcards

Module 4.5 - Quantum Physics Flashcards

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1
Q

In 1672, what did Isaac Newton believe light to be made of? Why?

A

> Light was made of corpuscles

> Supported his laws of motion; and reflection and refraction

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2
Q

In 1901, what did Max Planck hypothesise?

A

> Realised radiated energy couldn’t have continuous values

> Hypothesised that the total radiated energy were emitted in PACKETS with each having a fixed amount.

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3
Q

What did Einstein and De Broglie find in 1905?

A

> Einstein showed that atoms absorb and emit light

> De Broglie showed that light behaves as a wave and a particle.

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4
Q

Define Quantum (Pl - Quanta)

A

Small DISCRETE unit of ENERGY

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5
Q

Define Photon

A

A QUANTUM associated with EM radiation

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6
Q

What are the two equations to find the energy of a photon?

A 
E = hf    
E = hc ÷ lambda
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7
Q

What is E in E=hf?

A

E - energy - J

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8
Q

What is h in E=hf?

A

h - Planck’s constant - J/s

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9
Q

What is f in E=hf?

A

f - frequency - Hz

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10
Q

What is c in E=hc÷lambda?

A

c - wave speed - m/s

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11
Q

What is lambda in E=hc÷lambda?

A

lambda - wavelength - m

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12
Q

How do you work out the energy of n number of photons?

A

E = nhf

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13
Q

What is an Electron volt (eV)?

A

The KINETIC energy gained by ONE electron when it is accelerated through a p.d. of 1V

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14
Q

How do you work out the energy gained by an electron?

A

E = charge x p.d.

Charge of electron is 1.602x10^-19

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15
Q

What is 1eV equal to?

A

1.602x10^-19J

E=QV = 1.602x10^-19 x 1 = 1.602x10^-19J

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16
Q

J —> eV?

A

DIVIDE by 1.602x10^-19

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17
Q

eV—>J?

A

MULTIPLY by 1.602x10^-19

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18
Q

How much kinetic energy (in eV) does an electron of charge e have through a p.d. of 100v?

A

100eV

  1. 602x10^-19 x 100 = 1.602x10^-17J
  2. 602x10^-17 ÷ 1.602x10^-19 = 100eV
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19
Q

Derive eV = hc ÷ lambda

A

energy of a photon = energy of electrons that are excited in the semiconductor material of the LED.

E = hc ÷ lambda
Therefore
eV = hc ÷ lambda

20
Q

What is the photoelectric effect?

A

When EM radiation of a particular frequency is shone on the surface of a metal, electrons are emitted. The photons from the radiation causes electrons to be released as photoelectrons.

21
Q

How is the photoelectric effect demonstrated on an electroscope?

A

> Shining small amount of UV on zinc plate, causes electrons to be emitted from the negative zinc plate causing the angle between the gold leaf and the plate to decrease
But it doesn’t change when large amounts of VISIBLE light is shone

22
Q

Define Threshold frequency

A

The LOWEST frequency of radiation that will result in the emission of electrons from a particular metal surface

23
Q

Define Work Function

A

MINIMUM energy required to release an electron from the surface of a metal - energy to overcome the attraction between the electron and metal ions

24
Q

What happens if the incident radiation has a frequency below the threshold frequency?

A

The photons DO NOT have enough energy to overcome the work function of the metal

25
Q

What happens if the incident radiation has a frequency equal to the threshold frequency?

A

Causes the electrons to be OMITTED but with NO KE

26
Q

What happens if the incident radiation has a frequency above the threshold frequency?

A

Causes the electrons to OMITTED with SOME KE

27
Q

What happens if the incident radiation has a higher intensity whilst above the threshold frequency?

A

MORE electrons are omitted PER SECOND but WILL NOT affect KE

28
Q

What is Einstein’s Photoelectric equation?

A

hf = ø + KE max

29
Q

What is hf in Einstein’s Photoelectric equation?

A

hf is the energy of the incident photon where h is Planck’s constant

30
Q

What is ø (phi) in Einstein’s Photoelectric equation?

A

Ø is the work function of the metal

31
Q

What is KE max in Einstein’s Photoelectric equation?

A

KE max is the MAXIMUM kinetic energy of an electron once it has been ejected from the metal

32
Q

What were Einstein’s two main points on the Photoelectric effect?

A

> Each single photon could only eject one single electron

> Either the photon energy was LARGER than the work function; or SMALLER so the electron would remain on the metal.

33
Q

How do you determine the minimum frequency at which electrons are released?

A

hf = ø + KE max

At minimum frequency, only enough energy to release electron

KE max = 0
f0 = Threshold frequency
hf0 = ø
f0 = ø ÷ h

34
Q

What is KE max independent of in the photoelectric effect?

A

Intensity - it is not affected by the amount of photons coming in

35
Q

What is the rate of emission of photoelectrons (above threshold frequency) proportional to?

A

Intensity - the larger the number of photons coming in, the greater the rate of emission of photoelectrons.

36
Q

What portrays light to be a wave?

A

> Refraction

> Interference

37
Q

What portrays light to be a particle?

A

> The photoelectric effect

38
Q

What indicates waves acting like a particle?

A

hf = E - Frequency of a wave can give certain photons a certain energy

39
Q

What indicates particles acting as waves?

A

Electron Diffraction - an electron is a particle yet it can diffract like a wave. This is shown by firing electrons at a thin layer of graphite in a vacuum which creates a circular electron diffraction pattern

40
Q

Why must particles have a wavelength?

A

For electrons and other particles travel through space as a wave, they must have a wavelength

41
Q

How do you work out the wavelength of a particle?

A

lambda = h ÷ p = h ÷ mv

42
Q

What are the terms of the De Broglie Equation?

A 
lambda - wavelength 
h - Planck’s constant
p - momentum
m - relativistic mass (as v—>c , m increases)
v - velocity of particle
43
Q

What does the intensity of a wave at a point represent?

A

The probability of a particle being there

44
Q

How do electrons act like waves?

A

The way they travel through space

45
Q

How do electrons act like particles?

A

The way they interact, such as attraction.

A-level Physics (12 decks)

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