1
Q
Centre of gravity
A
The point through which any external applied force produces a straight line motion but no rotation
2
Q
Speed and drag relation?
A
Drag =ks2
3
Q
How does speed drag eq relate to terminal velocity
A
- when first out, only weight acting creating resultant downwards and acceleration
- as speed increases, so does drag through our eq
- drag increases and equals weight
- zero resultant force, no acceleration and falling at terminal velocity
4
Q
What is a moment
A
Force * perpendicular distance IN THE LINE OF ACTION
5
Q
Principle of moments
A
For body in rotational equil, the sum of anti-clockwise is equal to sum of clockwise about the same point
6
Q
Couple
A
A pair of forces which are parallel and in opposite directions in different lines
7
Q
Torque
A
The moment of a couple
8
Q
Pressure
A
The normal force exerted per unit area
9
Q
Archimedes Principle
A
The upthrust experienced on a body immersed in a fluid, is equal to the weight of the fluid it displaces
10
Q
Whenever pushing a body up
A
It is always transferred to GPE
11
Q
Energy is
A
SCALAR
12
Q
Power eq and WHY
A
F*v = when a constant force is applied on an object to maintain constant speed
13
Q
F=kx
A
Can be applied to any object that can be elastically compressed or stretched
14
Q
How to investigate hookes law
A
- attach spring at one end held by a G clamp or a large mass
- set up metre rule with resolution of 1mm to the spring
- suspend masses on one end, recording mass (F) and its extension
15
Q
How to improve accuracy of Hooke’s law experiment
A
- use a set square instead of ruler
- take reading at eye level to avoid parallax error
- use digital mass balance
- to obtain reliable results, take at least 6 diff readings and repeat
16
Q
If object has plastic deformation
A
Some of the work done has gone into moving it’s atoms to new permanent positions
17
Q
How rubber works
A
- it’s F x graph has a hysteresis loop; more work is done loading than unloading and so holds energy (work done on it)
- this is why its good as shock absorbers in airplane tyres
18
Q
Stress strain graph
A
- elastic limit
- yield 1 + 2 - where material extends rapidly
- UTS - max stress (force) it can hold when being stretched before it breaks
- breaking point - starts necking and becoming thin and point where it breaks
19
Q
Young modulus
A
Property of a material and so independent of its length
20
Q
Spring constant
A
Is not independent of its length and is higher when length is shorter
21
Q
Young mod experiment
A
- same set up, attaching mass for force and area taken by venier calliper
- extension against original length and all plotted
- grad in linear region is E
22
Q
When bullet fired from gun
A
Momentum is zero as it is opposite velocities
23
Q
How to minimise air resistance on a runway
A
Use an air track
24
Q
Elastic collions
A
- momentum, energy, and KE is conserved
25
Inelastic collisions
Mom, energy conserved NOT KE
26
What is newtons actual second law
The resultant force is directly prop to rate of change of momentum in the same direction
27
Impulse
Ft = change in mom
28
Figure out how electrons move in electrolysis
From neg (cathode) to pos (anode)
29
Number density
The number of free charge carriers per unit volume
30
Derivation of I = Anev
- current = charge / time
- charge = ne and in a given vol = neV / time
- using units = V / t is Area * velocity
- I = Anev
31
What does I = Anev show now then
V is inversely prop to area and in to the square of r
Indicating if wire is thin, electrons move faster
32
As area increases
More electrons able to move so greater current and less resistance
33
As length increases
More ions collide with so greater resistance and lower current
34
In electron gun
We assume electrons have negligible KE at cathode
35
How does resistance increase
- as current flows, wire gets hotter and temp increases
- the positive ions have more internal energy, and vibrate with greater amplitude about mean position
- the frequency of collions with charge carriers and ions increase
- charge c do work and transfer more energy across wire
36
Why does res increase in thr graph then
- as current increases, more electrons pass per second
- more collisions happen with e and ions
- when they collide, they transfer more energy (work done) on the ions
- that causes ions to vibrate more, increase in temp, and keep colliding with more electrons
37
Experiment to determine resistivity
- place wire in circuit and put voltmeter across it
- as you move voltmeter across increasing length, measure A and V to get resistance
- plot resistance against length
- work gradient as resistive / area
- multiply by wires cross sectional area
38
To investigate LDR’s
Put black tube around it to see exactly when it lights up
39
When batteries in parallel
Voltage stays same
40
When working out internal resistance
Current cannot get too high or raise temp as that will change resistance
41
How to work our internal resistance
- Put voltmeter around component
- using variable resistor, vary current and voltage
- plot V against I giving us gradient as -r and intercept as EMF
42
If we loading a potential divider circuit
If loaded with very low resistance, will decrease total resistance
43
Pros and cons of rheostat compared to potentiometer
Potentiometer - able to get a minimum value of 0 for current
- a wider range of currents produced
Rheostat - can’t get a minimum value of 0
- easier to connect
44
How does a progressive wave work
- particles move from equilibrium position
- particles exert a force on each other
- a displaced particle will experience a restoring force from it’s neighbours and pulled back to original position
45
Refraction of water waves
As depth gets shallower, the wavelength decreases and so velocity decreases
46
Diffraction
When a wave passes through gap (which is near size of its wavelength) or obstacle, it spreads out, only changing direction (not speed, frequency or wavelength)
47
Why can longitudinal waves not be plane polarised
The oscillations are always parallel to propagation so cannot be plane polarised. Their oscillations are limited to only one plane
48
Intensity
Is prop to Amplitude 2
49
Electromagnetic spectrum wavelength order
50
How does polarisation of light show that it is transverse
Only transverse can be plane polarised
51
What is the principle of superposition of waves
When two waves superposé, they produce a single wave whose instantaneous displacement is equal to the sum of the individual displacements of the waves
52
What is coherence
When two waves emitted have the same phase difference, formed when they have the same frequency
53
IN BETWEEN TWO NODES
The particles are moving in phase with each other, reaching their max displacement at same time
54
ON DIFFERENT SIDES OF NODES
particles are moving in antiphase
55
Progressive vs stationary
Energy transferred - no energy
Wavelength same
Phase changes across one complete cycle - describe how nodes and anti work
All have same amplitude - difference in node and anti
56
Two similarities of progressive and stationary waves
- both have vibrations/ oscillations
- both have wavelength, amplitude, frequency
57
What is fundamental frequency
Minimum frequency of a stationary wave for a string
58
How to form a stationary wave experiment
- connect speaker to signal generator
- position speaker in front of solid surface with microphone in between
- adjust frequency until number of nodes and anti are detected
- measure distance between adjacent antinodes as wavelength/ 2 so * 2
59
1st way to work out h
- work out at exact threshold pd for led to light up (use black tube)
- plot v against 1/wavelength
- gradient is hc/e so multiply by c/e
60
What is work function
Minimum energy required to free electron from surface of metal
61
Photons use
ONE TO ONE INTERACTION
62
If we increase intensity
We increase number of electrons emitted
63
If we increase frequency
We increase energy, so increase max KE
64
2nd way to work out h
Graph of E against frequency: using Einstein’s photoelectric effect eq
- y intercept is work function
- x intercept is threshold frequency
- grad is always h
65
Relating de broglie with KE
We see wavelength is inversely prop to h / root 2KE mass
66
Comparing wavelength of proton vs electron
As momentum of proton is greater, reduces wavelength, and makes it much harder to observe
67
Why does liquid in glass thermometer never give truely accurate reading even when they reach thermal equilibrium
- because thermometer is colder, there is a net flow of thermal energy from water to thermom
- this reduces the temp of the water
- this net flow stops when they reach thermal equil, which is ultimately lower temp than what it started at
68
What was Brownian motion
- collisions were elastic and resulted in transfer of momentum from water mols to the grains, resulting motion in haphazard ways
- shows the kinetic model - matter is made up of atoms and mols that have KE
69
Two ways to increase internal energy of a gas
- increase temp, increasing KE
- increase in potential energy - formed when change of state to s,l or l,g ie. Breaking its bonds gives RISE to PE
70
How to analyse temp time graphs for SHC
- e = mct
- e/t = mc t/t
- p = mc grad
- c = p /m*grad
71
When analysing constant volume flow
A given volume of liquid in a pipe is equal to a given mass
72
What is definition of SLH
The energy required to change phase of 1kg mass WHILE AT CONSTANT TEMP
73
relation between SLH of vaporisation compared to fusion
Latent of vaporisation will always be greater because more bonds get broken changing state from liquid to gas than solid to liquid
74
Assumptions of kinetic model of ideal gas
- gas contains large amount of mols moving in random directions at random speeds
- atoms occupy negligible volume compared to volume of gas
- collisions of atoms with each other and walls are perfectly elastic
- time taken to collide is negligible compared to time between collisions
- electrostatic forces are negligible except during collisions
75
How is pressure caused
- f = change in momentum / time
- f = -2mu / time
- pressure = f/area
76
How do isotherms look
- if at a higher temp - the inversely graph is further from axis
- for a p against 1/v - the gradient is steeper
77
Graph of pV against T
Gradient is nR however as R is constant, the greater the n, the steeper the grad
78
Derivation of pv = 1/3 Nm c2
79
Boltzmann of ideal gas
- peak = most probable
- next to it = average (mean)
- next to that = Crms
80
Top of ferris wheel forces
Centripetal = mg - N
81
Bottom of ferris wheel
Centripetal = N - mg
82
Forces in a pendulum
- F cos 0 = mg
- f sin 0 = centripetal = mv2/r
- so equating = tan 0 = v2/rg
83
What does pendulum show
The angle of the pendulum is not affected by mass of bob
84
Why must pv = nrt use kelvin
- temp must tend to zero
- this temperature scale is K
85
What is Brownian motion
- haphard motion
- due to collisions with particles
- transfer of momentum as it is elastic
- shows kinetic model that they have KE and matter made up of atoms
86
How to improve accuracy of SHC experiment
- insulate
- stir to avoid hotspots
- lagging the kettle
87
Why psi instead of p
Smaller divisions making it more accurate
88
What is centripetal force
Force acting perpendicularly to direction of motion
89
What happens if rate of rotation increases
T increases to provide greater centripetal force
90
How to measure centripetal force experiment
- use string with bung attached
- stopwatch to measure rime period
- suitable scale to measure rad
- whirl with constant frequency
- measure time and vary frequency
- expect v2 directly against r
- plot r against t-2
- with straight lime graph
91
Where might high shc be useful
- Car cooling systems because it absorbs large heat for small rises in temp
- helps maintain constant body temp
92
How does pressure increase volume decrease
- When gas heated mols have more KE
- more collisions, greater chnage of momentum and greater force
- constant pressure achieved by increasing volume
93
What are two properties of EM waves which others don’t have
- travel at C
- travel in vacuum
94
What wave phenomenon does both s and p waves have
- diffraction
- superposition
- refraction
95
How to polarise microwaves
- Place transmitter in front of receiver
- rotate of 90 and see how amplitude changes
- link observations on how I prop to a2
96
How is a stationary wave formed
- the wave incident is reflected
- the two waves superposé
- to produce series of nodes and anti nodes
97
If bright fringe
The waves are interfering constructively and so at a ngamma giving max amplitude
98
If dark fringe
The waves interfere destructively at a n+1gamma resulting in min amplitude
99
Coherence
Constant phase difference
100
How to work out number of photons in quantum
Power/energy
101
Potentiometer compared to fixed/variable resistor
Potentiometer - can get a min value of 0 current so wider range of voltages
- more sensitive
- easier to control current
Fixed - min current is only when resistor is 0, however due to resistor being fixed current can never be zero and so cannot produce wide range of values
102
What is the idea of de broglie
- where electrons have wavelike properties
- and their wavelength are dependant on their momentum
103
Difference of electron and photon
- electrons have mass photons dont
- electrons have charge
104
What is photoelectric effect
Emission of electrons from surface of metal when photons incident on them
105
What is internal resistance
Energy that is transferred into thermal loss of the battery
106
Hookes law
Extension is directly proportional to force in the elastic limit
107
Two quantities with same units
- moment
- torque
108
If we half the diameter how does force ext graph change
Area decreases by 4, so for same force, extension increases by 4, making the grad 4 times less steep
109
Always work out net force on spring to work out acceleration
110
Why F=ma does not work when fast speed
Mass changes (increases)
111
Why does acceleration not stay constant
- work done through drag
- work done through engine
112
Rocket increases acceleration
Because mass is decreasing.
113
Acceleration on a projectile
Is always downwards
114
If decelerating
R is greater than W
115
Two conditions for object in equilibrium
- zero net force
- zero net momentum
116
For Newton’s third law to work
- it must be the same nature of forces
- must be same force exerted on two different objects
Physics
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