Particles - Quantum phenomena

Photoelectric effect

Photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it

Threshold frequency

The minimum frequency of photons required for photoelectrons to be emitted from the surface of a metal plate through the photoelectric effect

How to increase number of photoelectrons emitted per second

• When frequency is above threshold, light intensity can be increased to increase photoelectrons per second

• Photoelectron only emitted if frequency above threshold

Work function

Minimum energy required for electrons to be emitted from the surface of the metal

Photon energy directly proportional to frequency

Stopping potential

Potential difference needed to apply across the metal to stop the photoelectrons with maximum kinetic energy

E_k(max) = eV_s

e = charge of electron

V_s = stopping potential

Fluorescent tube production of light explanation

This voltage accelerates free electrons through the tube, which collide with the mercury atoms causing them to become ionised, releasing more free electrons. The free electrons collide with the mercury atoms, causing them to become excited. When they de-excite they release photons, most of which are in the UV range. The (phosphorous) fluorescent coating on the inside of the tube, absorbs these UV photons and therefore electrons in the atoms of the coating become excited and de-excite releasing photons of visible light

Use of light from fluorescent tube

Pass visible light produced through diffraction grating/prism to form a line spectrum

Line spectrum

Each line represents different wavelength of light.

Only discrete values of wavelength so only photon energies emitted from fluorescent tube shown, thus evidence electrons can only transition between discrete energy levels

Line absorption spectrum

Produced via passing white light through cooled gas

Continuous spectrum of all possible wavelengths of light, with black lines at certain wavelengths (represent possible differences in energy levels since atoms in gas can only absorb photons of energy = difference between two energy levels)

Wave-particle duality examples (brief)

Wave: Diffraction (forms concentric rings), interference, polarisation, refraction

Particle: Photoelectric effect, collisions with other particles (annihilation etc), deflection by electromagnetic field

De broglie wavelength equation explanation of electron diffraction patterns

When momentum increases, wavelength decreases hence amount of diffraction decreases, so concentric rings of interference pattern become closer and vice versa