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1
Q

what lepton is consevred

A

Lepton number
Muon number
Electron number

2
Q

What interaction is strangeness not conserved

A

Weak

3
Q

What doesnt include protons in decay

A

Mesons

4
Q

Proton rich nucleus emits

A

Positron and neutrino

5
Q

W boson trains

A

0.001fm range non zero mass charge

6
Q

W+ –>

W- –>

A

e- + antiv (n->p)

e+ + v (p->n)

7
Q

Threshold frequency =

A

fmin=φ/h

8
Q

Photoelectric emmision

A

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

9
Q

Ekmax y axis

Frequency x axis

A

fmin x axis
-φ y intercept
h gradient

10
Q

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

A

Strong

Weak

11
Q

Beta decay is ___ interaction because

A

Weak as quark flavour not conserved

12
Q

Mev to J

A

1.6x10^-13

13
Q

Ev to J

A

1.6x10^-19

14
Q

Ionisation energy

A

Minimum energy required to eject an electron

15
Q

Electron volt means

A

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

16
Q

When is a photon emitted

A

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

17
Q

hf =

A

E1-E2

18
Q

Ionisation of atom

A

Atom loses an orbiting electron and becomes charged

19
Q

Excited atom means

A

Electron moved up to higher level

20
Q

Emission spectrum

A

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

21
Q

Absorption spectra

A

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

22
Q

In which part of the electromagnetic spectrum are the photons?

A

Ultraviolet

23
Q

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?

A

Free electrons collide with orbital electrons in atom transferring energy

24
Q

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?

A

(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

25
Q

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

A

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

26
Q

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.

A

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

27
Q

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.

A

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

28
Q

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

A

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

29
Q

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.

A

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)

30
Q

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.

A

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)

31
Q

How to prove that light is transverse

A

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

32
Q

How do polaroid sunglasses work

A

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.

33
Q

Define displacement

A

distance and direction from equilibrium position

34
Q

Define amplitude

A

maximum displacement of a vibrating particle

35
Q

Define wavelength

A

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

36
Q

Define frequency

A

number of complete waves passing a point per second, Hz

37
Q

Define period

A

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

38
Q

Why is a stationary wave formed with two nodes

A

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

39
Q

How are maxima and minima formed?

A

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)

40
Q

What happens during superposition of two waves

A

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

41
Q

Stationary waves are formed on a rope if…

A

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.

42
Q

Constructive interference is where

A

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

43
Q

Destructive interference is where

A

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

44
Q

Stationary waves are formed by

A

two waves with equal frequency travelling in opposite directions

45
Q

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

A

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

46
Q

Describe and explain the experiment portraying the photoelectric effect

A

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.

47
Q

potential divider

A

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

48
Q

Strangeness is conserved in

A

strong nuclear interactions

49
Q

% uncertainty =

A

actual uncertainty/measurement * 100%

50
Q

actual uncertainty of 3.5x10^3

A

0.1x10^3

51
Q

when finding fringe spacing

A

-1 from fringe number counted

52
Q

electron capture —> p + e- –>

A

n + Ve

53
Q

Newtons 3rd law =

A

equal and opposite reactions

54
Q

Newtons 2nd law

A

f=ma

55
Q

safety precaution of laser

A

don’t look directly at it

56
Q

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

A

vibrate in phase

57
Q

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

A

the weight

58
Q

work done by friction means that

A

energy transferred to thermal energy

59
Q

If angle of refraction is greater than angle of incidence then

A

ray bends away from normal

60
Q

Excitation -

A

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