Revision Flashcards
what lepton is consevred
Lepton number
Muon number
Electron number
What interaction is strangeness not conserved
Weak
What doesnt include protons in decay
Mesons
Proton rich nucleus emits
Positron and neutrino
W boson trains
0.001fm range non zero mass charge
W+ –>
W- –>
e- + antiv (n->p)
e+ + v (p->n)
Threshold frequency =
fmin=φ/h
Photoelectric emmision
Emission of electrons from metal surface when surface is illuminated by light of frequency>phi
Ekmax y axis
Frequency x axis
fmin x axis
-φ y intercept
h gradient
Hadrons are produced by what the ____ interaction and decay by the ____ interaction
Strong
Weak
Beta decay is ___ interaction because
Weak as quark flavour not conserved
Mev to J
1.6x10^-13
Ev to J
1.6x10^-19
Ionisation energy
Minimum energy required to eject an electron
Electron volt means
Work done when an electron moves through a pd of 1V
When is a photon emitted
When an atom de-excites due to an electron moving to an inner shell
hf =
E1-E2
Ionisation of atom
Atom loses an orbiting electron and becomes charged
Excited atom means
Electron moved up to higher level
Emission spectrum
All black but few lines where an electron is moving from a higher energy level to a lower energy level and emitting a photon of light with energy equal to the different in the two energy levels
Absorption spectra
When white light passes through a gas the gas absorbs particular wavelengths of light causing a few dark lines across an otherwise continuous spectrum
In which part of the electromagnetic spectrum are the photons?
Ultraviolet
A fluorescent tube is filled with mercury vapour at low pressure. After mercury atoms have been excited they emit photons. How do the mercury atoms in the fluorescent tube become excited?
Free electrons collide with orbital electrons in atom transferring energy
A fluorescent tube is filled with mercury vapour at low pressure. After mercury atoms have been excited they emit photons.
Why do the excited mercury atoms emit photons of characteristic frequencies?
(mercury) atoms have specific energy levels when electrons change levels they lose an specific amount of energy (photons emitted with specific amount of energy) (leading to photons of) specific frequencies
Explain why the kinetic energy of the emitted electrons has a maximum value
hf is a set energy available which has equal energy to photons - the energy required to remove the electron varies
When light of a certain frequency is shone on a particular metal surface, electrons are
emitted with a range of kinetic energies.
(a) Explain
• in terms of photons why electrons are released from the metal surface, and
• why the kinetic energy of the emitted electrons varies upto a maximum value.
The quality of your written communication will be assessed in this question.
energy is needed to remove an electron from the surface
work function φ (of the metal) is the minimum energy needed by
an electron to escape from the surface
light consists of photons , each of energy E = hf
one photon is absorbed by one electron
an electron can escape (from the surface) if hf > φ
kinetic energy of an emitted electron cannot be greater than hf – φ
an electron below the surface needs to do work/uses energy to reach
the surface
kinetic energy of such an electron will be less than hf – φ
The photoelectric effect suggests that electromagnetic waves can exhibit particle-like
behaviour. Explain what is meant by threshold frequency and why the existence of a
threshold frequency supports the particle nature of electromagnetic waves.
The quality of your written communication will be assessed in this question.
threshold frequency minimum frequency for emission of electrons
• if frequency below the threshold frequency, no emission
even if intensity increased
• because the energy of the photon is less than the work function
• wave theory can not explain this as energy of wave
increases with intensity
• light travels as photons
• photons have energy that depends on frequency
• if frequency is above threshold photon have enough energy
• mention of lack of time delay
Explain why the emitted electrons have a range of kinetic energies up to a maximum
value.
photons have energy dependent on frequency OR energy of photons constant
one to one interaction between photon and electron
Max KE = photon energy – work function in words or symbols
more energy required to remove deeper electrons
In a fluorescent tube, explain how the mercury vapour and the coating of its inner surface
contribute to the production of visible light. You may be awarded additional marks to those
shown in brackets for the quality of written communication in your answer.
mercury vapour at low pressure is conducting (1)
atoms of mercury are excited by electron impact (1)
producing (mainly) ultra violet radiation (1)
which is absorbed/ excites the coating (1)
which, upon relaxing, produces visible light (1)
electrons cascade down energy levels (1)
The atom in the ground state is given 5.00 × 10–17 J of energy by electron impact.
(i) State what happens to this energy.
(ii) Describe and explain what could happen subsequently to the electrons in the higher
energy levels.
the electron in the ground state leaves the atom (1)
with remaining energy as kinetic energy (0.89 × 10−17 J) (1)
(ii) the orbiting electrons fall down (1)
to fill the vacancy in the lower levels (1)
various routes down are possible (1)
photons emitted (1)
taking away energy (1)
How to prove that light is transverse
If you shine light through two polarising filters then as it passes the first one it becomes polarised and then passes through the second however as you rotate the second filter towards 90 degrees the intensity reduces until you cant see through it because its at a different plane showing that light is unpolarised and so transverse as longitudinal cannot be polarised because Propagation is parallel to wave movement so no planes so cannot be polarised or unpolarised through a filter
How do polaroid sunglasses work
Polaroid sunglasses reduce the flare of light reflected by water or glass. Such light is partly polarised when it reflects and so its intensity is reduced using Polaroid sunglasses.
Define displacement
distance and direction from equilibrium position
Define amplitude
maximum displacement of a vibrating particle
Define wavelength
least distance between two adjacent vibrating particles (with equal and simultaneous velocity and displacement)
Define frequency
number of complete waves passing a point per second, Hz
Define period
the time taken for one complete wave to pass a fixed point = 1/frequency
Why is a stationary wave formed with two nodes
Progressive waves travel from centre to ends and reflect, Waves have same frequency and amplitude, Superposition occurs, Waves move in opposite directions superpose and cancel at nodes
How are maxima and minima formed?
Superposition/interference occurs and waves of equal frequency travelling in opposite directions are reflected off the metal plate. Maxima are formed where waves are in phase (and interfere constructively) and minima are formed where waves are in antiphase (and interfere destructively)
What happens during superposition of two waves
When a wave is reflected from a fixed end it undergoes a 180 degree, superposition between the incident and reflected waves cause destructive interference at the nodes and constructive at the antinodes
Stationary waves are formed on a rope if…
two people send waves continuously along a rope from either end. The two sets of waves are referred to as progressive waves to distinguish them from stationary waves. They combine at fixed points along the rope to form points of no displacement or nodes along the rope. At each node, the two sets of waves are always 180degrees out of phase so they cancel each other out.
Constructive interference is where
the two waves are in phase with each other and constructively interfere to give a wave of greater amplitude
Destructive interference is where
the two waves are in anti-phase and destructively interfere to give a wave of zero amplitude
Stationary waves are formed by
two waves with equal frequency travelling in opposite directions
A rock is at the peak of a transverse wave describe its motion in one complete cycle
Oscillation perpendicular to the direction of wave travel
Oscillates from equilibrium to maximum positive displacement, back to equilibrium and then to negative maximum displacement and back to equilibrium
Describe and explain the experiment portraying the photoelectric effect
the gold foil drops to zero when the zinc plate has negative charge and illuminated by uv light because conduction electrons at the zinc surface leave the zinc surface when the uv light is directed at it. The emitted electrons are photoelectrons which take negative charge with them. If the zinc plates positively charged then the leaf rises and stays in position regardless of the uv light. If the electroscope is charged negatively or positively and visible light is directed at it the lead rises and stays in position.
potential divider
combination of resistors in series connected across a voltage source to produce a required a potential differnce
Strangeness is conserved in
strong nuclear interactions
% uncertainty =
actual uncertainty/measurement * 100%
actual uncertainty of 3.5x10^3
0.1x10^3
when finding fringe spacing
-1 from fringe number counted
electron capture —> p + e- –>
n + Ve
Newtons 3rd law =
equal and opposite reactions
Newtons 2nd law
f=ma
safety precaution of laser
don’t look directly at it
for a stationary wave, between two nodes, all parts of the wave
vibrate in phase
for a body in free fall, the rate of change of momentum =
the weight
work done by friction means that
energy transferred to thermal energy
If angle of refraction is greater than angle of incidence then
ray bends away from normal
Excitation -
electrons collide with orbital electrons transferring energy so move up energy level and lose set energy = hf
