Aqa a level physics paper 1 Study Guide

What is meant by work function (2) - ANSWERSMinimum energy required by an electron to escape from (1) a metal surface (1) What is meant by ionisation energy? (2) - ANSWERSMinimum 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) - ANSWERSEnergy 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? - ANSWERSDiffraction 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? - ANSWERSThe lowest energy state of an atom Explain the difference between excitation and ionisation (2) - ANSWERSAn 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) - ANSWERSdiscrete 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 - ANSWERSElectrons 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? - ANSWERSUV/ 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) - ANSWERSparticle 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) How does the strong nuclear force between two nucleons vary with the separation of the nucleons? (3) - ANSWERSrepulsive at 0.5 fm (1) attractive from 0.5 to 3 fm (1) above 3 fm, force 0 (1) What is meant by monochromatic light - ANSWERSlight of a single frequency What is meant by coherent - ANSWERSconstant phase difference Effect on diffraction pattern when wavelength decreases (3) - ANSWERSMaxima closer together (1) angle decreases (1) smaller path difference (1) What happens when white light is used in slits instead of monochromatic light? (4) - ANSWERSCentral bright fringe (maximum) is white (1) Fringes on either side are continuous spectra (1) Dark fringes would be closer together due to λred being larger than the average λwhite (1) Bright fringes (maxima) are wider How do diffraction patterns (fringes on the screen) form? - ANSWERSInterference (1) from light from two slits overlapping (superposition) (1) maxima where crests meet (constructive interference) (1) dark fringes/minima form where crest and trough meet (destructive interference) (1) Formation of a stationary wave - ANSWERSTwo waves superpose (1) same wavelength and/or frequency (1) Travelling with equal and opposite velocity (direction of movement) (1) stationary vs progressive waves (3 for each) - ANSWERSstationary: have nodes/antinodes (1) points between nodes all in phase (1) cannot transfer energy progressive: no nodes/antinodes (1) within one wavelength all points are out of phase (1) can transfer energy How does TIR transmit information in an optical fibre? (2+ diagram) - ANSWERSCore has higher refractive index than cladding (1) when incident light at a greater angle than critical angle of cladding TIR occurs (2) Observations of a polarisation filter rotation? ("What observations could be made when the filter in rotated through 360˚?") - ANSWERSVariation in intensity between maxima and minima (light and dark) (1) Two maxima and Two minima within 360 (1) define moment of a force (2) - ANSWERSforce x perpendicular distance around a pivot (1) between force and pivot (2) define center of gravity - ANSWERSthe point in a body (1) where the weight of an object appears to act (1) state principle of moments - ANSWERSfor a body in equilibrium (1) the sum of clockwise moments about a point (1) is equal to the sum of anticlockwise moments state the principle of conservation of momentum - ANSWERStotal momentum before = total momentum after (1) in an isolated system (no external force) state the relationship between the force acting on a body and the momentum of the body - ANSWERSforce proportional to rate of change of momentum define center of mass - ANSWERSthe point in the body through which the mass appears to act conditions for equilibrium - ANSWERSresultant force is 0 (1) resultant torque is 0 (1) difference between scalar and vector - ANSWERSvector has magnitude and direction scalar only has magnitude definition of elastic limit - ANSWERSmaximum force/load which can be applied to the object without it being permanently deformed define hookes law - ANSWERSExtension is proportional to the applied force up to limit of proportionality (1) as long as extension is small (1) newton's first law - ANSWERSobject in motion remains in motion and object stationary remains stationary till external force acts on it newton's second law - ANSWERSf=ma newton's third law - ANSWERSevery action has an equal and oppisite reaction define yield stress of a material - ANSWERSforce per unit area (1) at which material permanently deformed (1) for no/small increase in force define density of a material - ANSWERSmass per unit volume explain what is meant by spring constant (k) - ANSWERSforce divided by extention state what is meant by a superconductor (2) - ANSWERSconductor which has 0 resistance (1) at critical temperature (1) state what is meant by the emf of a battery (1) - ANSWERSenergy changed to electrical energy per unit charge define potential difference - ANSWERSwork done per unit charge explain why the use of superconductors would improve the efficiency of power stations and hence reduce carbon dioxide emissions - ANSWERSless energy lost (In conducting wires) (1) less fuel needed (1) explain what is meant by a potential divider - ANSWERSa combination of resistors across a voltage source to produce a required pd state what is meant by 'non-ohmic' - ANSWERSresistance not constant (V not directly proportional to I) example of non-ohmic conductor - ANSWERSfilament lamp/LDR/thermistor Advantage of using a stranded cable rather than a solid cable of the same cross-sectional area - ANSWERSlarger surface area so better heat dissipation Explain what is meant by resonance (4) - ANSWERSdriving frequency = natural frequency (1) vibrations of large amplitude produced (1) max energy transferred at resonance (1) phase difference between driver and oscillator is 90 degrees (pi/2 rads) Explain what is meant by forced vibrations (5) - ANSWERSforced vibrations = periodic force applied (1) frequency determined by as frequency of oscillator (1) phase difference is 180 degrees (pi rads) (1) frequency of driver frequency of oscillator (1) amplitude small at high frequency and vice versa explain what is meant by damping - ANSWERSremoves energy from oscillating system (OR when force opposes motion of oscillator) how does damping affect resonance - ANSWERSreduces amplitude at resonant frequency name two types of potential energy involved when a mass-spring system performs vertical SHM - ANSWERSelastic potential and gravitational potential describe what is meant by the period of an oscilation - ANSWERStime taken for one complete oscillation state conditions necessary for SHM (2) - ANSWERSacceleration proportional to displacement (1) directed towards mean position A particle that moves uniformly in a circular path is accelerating yet moving at a constant speed. Explain this statement by reference to the physical principles involved (4) - ANSWERSspeed scalar velocity vector (1) direction changes continuously (1) velocity changes (1) acceleration is rate of change of velocity What is meant by damping - ANSWERSWhen force opposes motion