Stupid CAIE Quantum Mark Schemes | Quizlet

Photon

* Packet / quantum / discrete amount of energy

* Of electromagnetic radiation

* E = hf (Energy = Planck's Constant × Frequency)

Work Function Energy

* Minimum energy

* To remove / cause emission of an electron from the surface of the metal

Threshold Frequency

* Lowest/minimum frequency of electromagnetic radiation

* Giving rise to the emission of electrons from the surface

de Broglie Wavelength

* Wavelength of a wave associated with a particle

* That is moving

Quantisation of Charge

* Charge exists in discrete and equal quantities

* Or: Integral multiples of the elementary charge 1.6×10^-19 C

Evidence for Particulate Nature of EM Radiation

*Wave theory predicts any frequency would give rise to emission of electrons if exposure time is sufficiently long.

*A photon has a specific value of energy dependent on frequency.

*Emission only occurs if photon energy is greater than the threshold/work function/energy to remove electron from surface.

*A single photon interacts with a single electron and is absorbed instantaneously.

Why Most Electrons Have Less Than Maximum KE

*Photon interaction with electron may occur below the surface.

*Energy is required to bring the electron to the surface (so less KE remains).

Evidence for Wave Nature of Particles

*Electron/particle diffraction.

*Concentric rings are observed, which is a diffraction pattern.

*Diffraction is a wave property / the pattern is similar to that observed with visible light.

Effect of Increasing Speed on Diffraction Rings

*Speed increases, so momentum increases.

*λ = h/p, so λ decreases.

*Therefore ring diameter/radii decrease.

Emission Spectrum as Evidence for Discrete Energy Levels

*Each (coloured) line corresponds to a specific/particular photon energy/wavelength.

*A photon is emitted when an electron changes its energy level / de-excites.

*Discrete/specific wavelengths imply specific energy changes, therefore discrete energy levels.

Why immediate emission does not support wave theory

For a wave, an electron would collect energy continuously. For a wave, electron would always eventually be emitted at all frequencies (after a long enough delay).

*But electrons are either emitted immediately or not at all / no time delay is observed.

Effect of decreasing wavelength at constant intensity on maximum KE

*Photons have higher energy

*So maximum KE increases.

Effect of decreasing wavelength at constant intensity on number of electrons / maximum current

*Fewer photons per unit time (since same intensity but higher energy per photon)

*So fewer electrons emitted per unit time / maximum current decreases.

Effect of decreasing intensity at constant wavelength on maximum KE

*Photons have same energy so max KE is unchanged.

Effect of decreasing intensity at constant wavelength on number of electrons / maximum current

*Fewer number of photons per unit time

*So the number of electrons / current decreases in proportion to decrease in intensity

Absorption Spectrum in Gas

*Spectrum appears as a continuous spectrum crossed by dark lines.

*Two dark lines (at specific wavelengths).

*Electrons in the gas absorb photons with energies equal to the excitation energies.

*The absorbed photons are re-emitted in all directions, so less light reaches the observer in the forward direction.