Quantum Phenomena Flashcards
Threshold Frequency
The minimum frequency of incident light which can cause photoelectric emission. It is equal to workfunction/planks constant.
Work Function
Minimum energy needed by an electron to escape the metal surface
Quantisation
When only certain levels of energy are allowed
Why is ke a maximum?
Photons have energy dependent on frequency (e = hf).
One to one interaction between photon and electron.
Max KE = photon energy – work function.
More energy required to remove deeper electrons
State and explain the effect on the emitted electrons by increasing the frequency of the light
the (maximum) kinetic energy of released electrons increases this is because increasing the frequency of the photons increases their energy
State and explain the effect on the emitted electrons by increasing the intensity of the light
The number of electrons emitted (per second) increases because there are now more photons striking the metal surface(per second)
Explain how the photoelectric effect produces evidence which illustrates the particulate nature of light.
Energy to remove electron supplied by electromagnetic radiation if photon energy below threshold: no photoelectron. Increasing intensity of electromagnetic radiation increases number of photoelectrons
Explain why the photoelectric effect cannot be explained by the wave theory of light.
If it could, there would be photoemission below threshold frequency (even with bright light) because theory would allow gradual accumulation of energy to cause emission.
State what is meant by ground state
When electrons/atoms are in their lowest/minimum energy level
Explain the difference between excitation and ionisation.
In either case, an electron receives (exactly the right amount of) energy excitation promotes an (orbital) electron to a higher energy/up a level. Ionisation occurs when an electron receives enough energy to leave the atom
An atom can also become excited by the absorption of photons. Explain why only photons of certain frequencies cause excitation in a particular atom
Electrons occupy discrete energy levels and need to absorb an exact amount of/enough energy to move to a higher level. Photons need to have a certain frequency to provide this energy (e = hf ). Energy required is the same for a particular atom. All energy of photon absorbed in 1 to 1 interaction or clear a/the photon and an/the electron
What is meant by an excited atom
An electron/atom is at a higher level than the ground state
Describe the process by which mercury atoms become excited in a fluorescent tube
Electrons (or electric current) flow through the tube and collide with electrons raising the electrons to a higher level (in the mercury atoms)
State what happens in an atom when line spectra are produced.
Electrons move from one energy level emitting or absorbing a definite frequency / wavelength / colour or photon energy(of electromagnetic radiation)
State what is meant by the photoelectric effect.
Release of electrons from (metal) surface when electromagnetic radiation is incident on the surface
