Physics Paper 1 Flashcards
What is meant by work function?
Minimum energy required by an electron to escape from a metal surface.
What is meant by ionisation energy?
Minimum energy required to remove an electron from an atom from the ground state.
Why do emitted electrons have a kinetic energy that varies up to a maximum value?
Energy of a photon is fixed/constant. Energy is required for electrons to overcome work function ø. Electrons deeper into/below the surface of the metal require more energy to overcome work function and therefore have less KE. Maximum KE = Energy of photon - work function ø.
Explain how (bright ring) diagram is evidence of the wave-particle duality of electrons?
Diffraction pattern maxima/minima (bright and dark areas). Diffraction is a property of waves - proves wave-behaviour of electrons.
What is meant by the ground state?
The lowest energy state of an atom.
Explain the difference between excitation and ionisation.
An electron receives a discrete amount of energy for BOTH. 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.
Discrete energy levels. Electrons need to absorb a DISCRETE amount of energy to move to a higher energy level. Photons need to have a certain frequency to provide this energy, because E=hf. Interaction is a 1:1 reaction; all of the photon’s energy is absorbed.
Explain how excitation takes place in a fluorescent tube.
Electrons flow through the tube to the applied PD causing a current to flow. Electrons collide with mercury atoms in the tube. This raises electrons in the mercury atom to a higher energy level.
What is the purpose of coating in a fluorescent tube?
UV/High energy photons emitted from mercury atoms when the electrons in the atom de-excite. High energy photons absorbed by the coating. Coating emits photons in the visible spectrum.
What happens when annihilation occurs?
Particle and an anti-particle collide and cease to exist. Their mass is released as energy in the form of a pair of gamma photons.
How does the strong nuclear force between two nucleons vary with the separation of the nucleons?
Repulsive at < 0.5 fm. Attractive from 0.5 to 3 fm. Above 3 fm, force = 0.
What is meant by monochromatic light?
Light of a single frequency.
What is meant by coherent?
Constant phase difference.
Effect on diffraction pattern when wavelength decreases?
Maxima closer together. Angle decreases. Smaller path difference.
What happens when white light is used in slits instead of monochromatic light?
Central bright fringe (maximum) is white. Fringes on either side are continuous spectra. Dark fringes would be closer together due to λred being larger than the average λwhite. Bright fringes (maxima) are wider.
How do diffraction patterns (fringes on the screen) form?
Interference from light from two slits overlapping (superposition). Maxima where crests meet (constructive interference). Dark fringes/minima form where crest and trough meet (destructive interference).
Formation of a stationary wave?
Two waves superpose. Same wavelength and/or frequency. Travelling with equal and opposite velocity (direction of movement).
Stationary vs progressive waves?
Stationary: have nodes/antinodes. Points between nodes all in phase. Cannot transfer energy. Progressive: no nodes/antinodes. Within one wavelength all points are out of phase. Can transfer energy.
How does TIR transmit information in an optical fibre?
Core has higher refractive index than cladding. When incident light at a greater angle than critical angle of cladding, TIR occurs.
Observations of a polarisation filter rotation?
Variation in intensity between maxima and minima (light and dark). Two maxima and two minima within 360.
Define moment of a force.
Force x perpendicular distance around a pivot between force and pivot.
Define center of gravity.
The point in a body where the weight of an object appears to act.
State principle of moments.
For a body in equilibrium, the sum of clockwise moments about a point is equal to the sum of anticlockwise moments.
State the principle of conservation of momentum.
Total momentum before = total momentum after in an isolated system (no external force).
