Quantum

5.0(1)
studied byStudied by 9 people
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/20

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

21 Terms

1
New cards

Photon

A quantum of electromagnetic energy

2
New cards

Work function

The minimum energy needed to remove a single electron from the surface of a particular metal

3
New cards

Threshold frequency (f0)

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

4
New cards

Planck’s constant

6.63 × 10-34 Js (in formula book)

5
New cards

Electron volt

  • Energy transferred to or from an electron when it passes through a p.d. of 1 volt

  • 1 eV = 1.60×10-19J

6
New cards

Photoelectric effect

The emission of photoelectrons from a metal surface when electromagnetic radiation above a threshold frequency is incident on the metal

7
New cards

Photoelectron

Electrons emitted from the surface of a metal by the photoelectric effect

8
New cards

Evidence to suggest electromagnetic radiation is a wave

Evidence:

  • It can diffract, reffract and interfere with other EM ___

9
New cards

Evidence to suggest light is a particle

Evidence:

  • The photoelectric effect

10
New cards

Evidence to suggest electrons are waves

Evidence:

  • They can be diffracted

11
New cards

Evidence to suggest electrons are particles

Evidence:

  • They can be accelerated and deflected by magnetic and electric fields

12
New cards

Equation for photon energy in terms of frequency

E = hf

13
New cards

Equation for photon energy in terms of wavelength

E = hc/λ

14
New cards

Effect of increasing intensity of the light source while keeping the frequency constant on the photoelectric effect

If the frequency is greater than or equal to the threshold frequency:

  • Increases the rate of emission of photoelectrons.

  • Has no affect on their maximum KE

Otherwise, when less than the threshold frequency:

  • No change; still no electrons emmitted

15
New cards

Eintstein’s photoelectric effect equation

hf = ϕ + KEmax

16
New cards

What must be true for the photoelctric effect to happen

Energy of photon > work function / frequency of photon > threshold frequency

17
New cards

The behaviour of electrons which demonstrates that they have wave properties.

  • When electrons are passed through a thin slice of graphite they produce circular interference fringes on a flourescent screen. This demontstrates they are diffracted.

  • Diffraction of electrons occurs when the wavelength is similar to the gap size

  • Changes in the electron's speed/energy change the size of the ring / interference fringe spacing

  • Electrons have a (de Broglie) wavelength given by λ=h/p

18
New cards

How does increasing the electron’s speed/energy affect the circular interference pattern produced

  • Higher speed/energy means smaller de Broglie wavelength

  • Smaller wavelength means less diffraction

  • Smaller wavelength gives shorter path difference between areas of constructive and destructive interference

  • As such the rings become closer together (not just ‘smaller’)

  • They also become brighter because the electrons have more energy to transfer to the flourescent screen

19
New cards

How does decreasing the electron’s speed/energy affect the circular interference pattern produced

  • Lower speed/energy means larger de Broglie wavelength

  • Larger wavelength gives longer path difference between areas of constructive and destructive interference

  • As such the rings become further apart

  • They also become dimmer because the electrons have less energy to transfer to the flourescent screen

20
New cards

How is the work function related to the threshold frequency?

  • A photon with less than the threshold frequency f0 cannot cause electron emission

  • As such work function = h (threshold frequency)

21
New cards

Explain how Einstein's theory explains the observations of the photoelectric effect and how they demonstrate the particle-like behaviour of electromagnetic waves.

  • Individual photons are absorbed by individual electrons in the metal surface in a one to one interaction.

  • Only photons with energies above the work function energy will cause photoelectron emission

  • Photon energy is proportional to frequency

  • Hence UV photons or blue photons with higher frequency have higher energy so will cause photoemission but red photons will not.

  • Number of electrons emitted depends on light intensity

  • A wave model does not explain instantaneous emission of electrons.

  • A wave model does not explain a threshold frequency for emission to occur

  • hf - ϕ = KEmax is the equation resulting from conservation of energy. This can be rearranged to get Einstein’s photoecetric effect equation.