Revision

Question 1

what lepton is consevred

Answer 1

Lepton number
Muon number
Electron number

Question 2

What interaction is strangeness not conserved

Answer 2

Weak

Question 3

What doesnt include protons in decay

Answer 3

Mesons

Question 4

Proton rich nucleus emits

Answer 4

Positron and neutrino

Question 5

W boson trains

Answer 5

0.001fm range non zero mass charge

Question 6

W+ –>

W- –>

Answer 6

e- + antiv (n->p)

e+ + v (p->n)

Question 7

Threshold frequency =

Answer 7

fmin=φ/h

Question 8

Photoelectric emmision

Answer 8

Emission of electrons from metal surface when surface is illuminated by light of frequency>phi

Question 9

Ekmax y axis

Frequency x axis

Answer 9

fmin x axis
-φ y intercept
h gradient

Question 10

Hadrons are produced by what the ____ interaction and decay by the ____ interaction

Answer 10

Strong

Weak

Question 11

Beta decay is ___ interaction because

Answer 11

Weak as quark flavour not conserved

Question 12

Mev to J

Answer 12

1.6x10^-13

Question 13

Ev to J

Answer 13

1.6x10^-19

Question 14

Ionisation energy

Answer 14

Minimum energy required to eject an electron

Question 15

Electron volt means

Answer 15

Work done when an electron moves through a pd of 1V

Question 16

When is a photon emitted

Answer 16

When an atom de-excites due to an electron moving to an inner shell

Question 17

hf =

Answer 17

E1-E2

Question 18

Ionisation of atom

Answer 18

Atom loses an orbiting electron and becomes charged

Question 19

Excited atom means

Answer 19

Electron moved up to higher level

Question 20

Emission spectrum

Answer 20

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

Question 21

Absorption spectra

Answer 21

When white light passes through a gas the gas absorbs particular wavelengths of light causing a few dark lines across an otherwise continuous spectrum

Question 22

In which part of the electromagnetic spectrum are the photons?

Answer 22

Ultraviolet

Question 23

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?

Answer 23

Free electrons collide with orbital electrons in atom transferring energy

Question 24

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?

Answer 24

(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

Question 25

Explain why the kinetic energy of the emitted electrons has a maximum value

Answer 25

hf is a set energy available which has equal energy to photons - the energy required to remove the electron varies

Question 26

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.

Answer 26

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

Question 27

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.

Answer 27

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

Question 28

Explain why the emitted electrons have a range of kinetic energies up to a maximum
value.

Answer 28

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

Question 29

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.

Answer 29

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)

Question 30

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.

Answer 30

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)

Question 31

How to prove that light is transverse

Answer 31

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

Question 32

How do polaroid sunglasses work

Answer 32

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.

Question 33

Define displacement

Answer 33

distance and direction from equilibrium position

Question 34

Define amplitude

Answer 34

maximum displacement of a vibrating particle

Question 35

Define wavelength

Answer 35

least distance between two adjacent vibrating particles (with equal and simultaneous velocity and displacement)

Question 36

Define frequency

Answer 36

number of complete waves passing a point per second, Hz

Question 37

Define period

Answer 37

the time taken for one complete wave to pass a fixed point = 1/frequency

Question 38

Why is a stationary wave formed with two nodes

Answer 38

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

Question 39

How are maxima and minima formed?

Answer 39

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)

Question 40

What happens during superposition of two waves

Answer 40

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

Question 41

Stationary waves are formed on a rope if…

Answer 41

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.

Question 42

Constructive interference is where

Answer 42

the two waves are in phase with each other and constructively interfere to give a wave of greater amplitude

Question 43

Destructive interference is where

Answer 43

the two waves are in anti-phase and destructively interfere to give a wave of zero amplitude

Question 44

Stationary waves are formed by

Answer 44

two waves with equal frequency travelling in opposite directions

Question 45

A rock is at the peak of a transverse wave describe its motion in one complete cycle

Answer 45

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

Question 46

Describe and explain the experiment portraying the photoelectric effect

Answer 46

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.

Question 47

potential divider

Answer 47

combination of resistors in series connected across a voltage source to produce a required a potential differnce

Question 48

Strangeness is conserved in

Answer 48

strong nuclear interactions

Question 49

% uncertainty =

Answer 49

actual uncertainty/measurement * 100%

Question 50

actual uncertainty of 3.5x10^3

Answer 50

0.1x10^3

Question 51

when finding fringe spacing

Answer 51

-1 from fringe number counted

Question 52

electron capture —> p + e- –>

Answer 52

n + Ve

Question 53

Newtons 3rd law =

Answer 53

equal and opposite reactions

Question 54

Newtons 2nd law

Answer 54

f=ma

Question 55

safety precaution of laser

Answer 55

don’t look directly at it

Question 56

for a stationary wave, between two nodes, all parts of the wave

Answer 56

vibrate in phase

Question 57

for a body in free fall, the rate of change of momentum =

Answer 57

the weight

Question 58

work done by friction means that

Answer 58

energy transferred to thermal energy

Question 59

If angle of refraction is greater than angle of incidence then

Answer 59

ray bends away from normal

Question 60

Excitation -

Answer 60

electrons collide with orbital electrons transferring energy so move up energy level and lose set energy = hf