aqa a level physics paper 1 Questions & Answers(RATED A)

What is meant by work function (2) - ANSWERMinimum energy required by an electron to escape from (1) a metal surface (1) What is meant by ionisation energy? (2) - ANSWERMinimum energy required to remove an electron from an atom (1) from the ground state (1) Why do emitted electrons have a kinetic energy that varies up to a maximum value? (4) - ANSWEREnergy of a photon is fixed/constant (1) Energy is required for electrons to overcome work function ø (1) Electrons deeper into/below the surface of the metal require more energy to overcome work function and therefore have less KE(1) Maximum KE = Energy of photon - work function ø (1) Explain how (bright ring) diagram is evidence of the wave-particle duality of electrons? - ANSWERDiffraction pattern maxima/minima (bright and dark areas) (1) Diffraction is a property of waves- proves wave-behaviour of electrons (1) What is meant by the ground state? - ANSWERThe lowest energy state of an atom Explain the difference between excitation and ionisation (2) - ANSWERAn electron receives a discrete amount of energy for BOTH (1) Excitation promotes an electron to a higher energy level Ionisation is when an electron receives enough energy to leave the atom Explain why only photons of certain frequencies cause excitation (4) - ANSWERdiscrete energy levels (1) Electrons need to absorb a DISCRETE amount of energy to move to a higher energy level (1) Photons need to have a certain frequency to provide this energy, because E=hf (1) interaction is a 1:1 reaction all of the photon's energy is absorbed (1) Explain how excitation takes place in a fluorescent tube - ANSWERElectrons flow through the tube to the applied PD causing a current to flow (1) Electrons collide with mercury atoms in the tube (1) This raises electrons in the mercury atom to a higher energy level (1) What is the purpose of coating in a fluorescent tube? - ANSWERUV/ High energy photons emitted from mercury atoms when the electrons in the atom de-excite (1) High energy photons absorbed by the coating (1) Coating emits photons in the visible spectrum (1) What happens when annihilation occurs? (2) - ANSWERparticle and an anti-particle collide and cease to exist (1) Their mass is released as energy in the form of a pair of gamma photons (1)