Quantum Physics Part 1 - Photoelectric effect

Photoelectric Effect

• Electrons absorb energy from incident EM radiation.
• Electrons are emitted when they get enough energy causing current to flow in the circuit.
• The emitted electrons are called photoelectrons.
• *Photoelectric effect is the phenomenon where electrons are emitted from a metal surface when electromagnetic radiation of sufficiently high frequency is incident on the surface.
• *Photoelectric Experiment Setup:
• When radiation of sufficiently high frequency (greater than threshold frequency) is incident on the emitter plate E, it will emit electrons.
• The variable voltage source maintains electrodes at different know potentials. The emitted electrons from E (that have sufficient energy) will travel to the collector C and a current (known as photocurrent) will be detected by the ammeter as the electrons complete the loop in the circuit.
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• Pie de imagen: Fig 1. The Photoelectric Experiment

Photon

• A photon is a discrete bundle (or quantum) of electromagnetic energy.
• E: energy of a single photon
• - dependent on frequency
• - for a given frequency, a beam of EM radiation of greater intensity simply means more photons per unit time and not greater energy
• Total E = total energy of all the photons
• n: no. of photons passing a unit area per unit time
• Work function energy φ of a material is defined as minimum amount of the energy necessary to remove an electron frm the surface of the material.
• range of kinetic energies, more energy required to let electrons below the surface to escape
• By principle of conservation of energy, photo energy absorbed is converted to maximum KE after overcoming work function of metal.
• 
• Pie de imagen: Fig 2. equations for photoelectric effect

Quantum Analysis of the Photoelectric Effect

• When an EM radiation is directed at a metal surface, a stream of particles bombards the surface of the metal.
• Any free electron near the surface could absorb an incoming photon and gain all the energy of the photon.* (a photon must be absorbed as a whole by a single electron. Absorb all or nothing.
• If the gain in energy is sufficient, the electron can leave the plate. (escape)
• A photon that is not absorbed will be reflected or transmitted.
• Electrons are emitted INSTANTANEOUSLY:
• all the photon energy is delivered immediately to the electron in a single absorption hence no time delay and is independent on the intensity of the incident radiation.

Threshold frequency

• MINIMUM frequency of the incident radiation for the electron to escape.
• i.e. MAXIMUM wavelength of the incident radiation for the electron to escape
• For photoelectric emission to occur, f > threshold f or λ < threshold λ