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A Level Mid Terms > physics > Flashcards

physics Flashcards

1
Q

equation for force and energy in a spring

A 
F = kx  
E = 1/2 kx^2 = 1/2 Fx
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2
Q

what is a coherent wave?

A

waves that have the same frequency and maintain constant phase relationship/ have the same wavelength

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3
Q

when waves a and b are on a displacement/ distance graph, which one is ahead?

A

the one that is shifted to the left

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4
Q

when asked about phase relationship of two waves, what are the two things you need to include?

A

which one is ahead/ behind and by how much

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5
Q

what two things do you need from both sources to see a clear interference?

A

coherent waves and similar amplitudes

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6
Q

what equation links wavespeed, tension and mass per length?

A

v = √T/μ

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7
Q

what is the equation for intensity?

A

I = power / area

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8
Q

what is refraction?

A

when a wave changes speed, direction and hence wavelength as it passes into a different medium. (frequency stays constant)

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9
Q

which way does light bend when travelling through a medium?

A

low to high n: bends towards normal

high to low n: bends away from normal

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10
Q

how does light change with different angles of incidence?

A

i < r: refraction
i > r: TIR
i = r: 90 degree refraction

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11
Q

what is the difference between spectra and the photoelectric effect?

A

the photoelectric effect removes electrons from the surface of a metal with UV light.
spectra excites electrons but they are not emitted

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12
Q

what is the dE bRoCcOLi hypothesis?

A

all waves have a wave and particle nature and λ = h/p

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13
Q

what do you need to change to make an ultrasound more detailed?

A

decrease wavelength or increase frequency to do so.

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14
Q

how do you change electron volts to joules and vice versa?

A

q is 1.6*10^-19, electron volts is v and joules is E.
E = vq
or v = E/q

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15
Q

what is an energy band?

A

a discrete energy level electrons are allowed to exist at within an atom.

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16
Q

how is the emission and absorption spectra used?

A

emission spectra shows light given off deexcited electrons is diffracted and split up into the discrete wavelengths its made of. (electrons exciting hot gas)
absorption spectra diffracts light that has travelled through a gas to show the missing wavelengths. (light shone through cold gas)

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17
Q

what is Snell’s Law?

A

n1 sinθ1 = n2 sinθ2

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18
Q

what is the refractive index for air?

A

1

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19
Q

what are converging and diverging lenses?

A

they make parallel waves meet / move apart

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20
Q

what is d and n in nλ = d sinθ?

A

d: 1 / lines per mm (distance between lines)
n: order of diffraction

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21
Q

why does velocity change diffraction angle?

A

λ = h/p so increasing v decreases λ

less λ means less θ because nλ = d sinθ

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22
Q

how do you know what type of lens is producing a virtual image?

A

if the object is between the focal length and the lens, its a converging lens. otherwise a diverging lens

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23
Q

what does the IV graph of a diode look like?

A

curves up from following the x axis at a positive x value

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24
Q

what does the IV graph of a filament bulb look like?

A

S shape through the origin

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25
Q

what does the IV graph of a thermistor look like?

A

backwards S shape through the origin

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26
Q

what are Kirchoff’s 1st and 2nd laws?

A

current into a component= current out

adding the voltage of all components= battery voltage

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27
Q

what does the circuit symbol for a thermistor look like?

A

line below that bends through a rectangle resistor

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28
Q

what does the symbol for an LDR look like?

A

a resistor in a circle with two arrows pointing to it at an angle from above

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29
Q

what does the symbol for a variable resistor look like?

A

a diagonal arrow through a rectangular resistor

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30
Q

what is Newton’s 1st law?

A

objects remain at constant velocity unless a resultant force is acting on it

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31
Q

what is Newton’s 2nd law?

A

acceleration is proportional to force (F = ma)

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32
Q

what is Newton’s 3rd law?

A

for every force on an object, that object exerts an equal and opposite force of the same type

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33
Q

what is the law of the conservation of momentum

A

momentum before = momentum after (unless an external force acts)

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34
Q

what is work done a form of?

A

energy

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35
Q

how do you find the work done from a variable force / displacement graph?

A

area under the graph

36
Q

what is the difference between the yield point and elastic limit?

A

elastic limit is the last point where the material will return to its original shape. yield point is where it starts to deform without any extra load.

37
Q

what does tough mean?

A

lots of energy required to break (dynamic load)

large area under the graph

38
Q

what does strong mean?

A

lots of force required to break (static load)

breaking point high up on graph

39
Q

what does stiff mean?

A

lots of force required to strain (extend)

40
Q

what does hard mean?

A

hard to scratch

41
Q

what is diffraction?

A

when waves spread and change direction as they pass through a narrow gap or moves around an obstacle

42
Q

what is superposition or interference?

A

When two waves meet at the same point in space and the total displacement at that point becomes the sum of the individual displacements

43
Q

what is stoke’s law, what do the letters stand for and when does it apply?

A

F = 6πηrv
F: Force (frictional force/ viscous drag force)
η: Viscosity
r: Radius of object
v: Terminal velocity
Only applies when flow is laminar, object is small and spherical and speed is low

44
Q

what are the two equations for ω?

A

2π/T

θ/t

45
Q

what are the equations for x, v and a in circular motion and how do we find their maximum value?

A

x = A cos(ωt)
v = -Aω sin(ωt)
a = -Aω² cos(ωt)
they are at max when cos or sin=1

46
Q

which way do field lines go?

A

north to south

47
Q

what is magnetic flux density measured in?

A

Tesla or Wbm^-2

48
Q

what is the equation for magnetic flux density

A

Φ = BA cosθ

where Φ is magnetic flux

49
Q

what is the equation for force on wire in a magnetic field and what do the letters mean?

A 
F = BIL
F: force
B: Magnetic flux density
I: current
L: length of wire
50
Q

how is a motor made?

A

loop of wire with current flowing in magnetic field. direction of current changes every half turn due to split ring commutator.

51
Q

how does a dynamo work?

A

wire is manually turned in a magnetic field and an A.C. output is generated. This is because if wire experiences CHANGE in magnetic flux density, current is produced.

52
Q

how do transformers work and what are the equations associated with them?

A

alternating current is wrapped around an iron core which induces a magnetic field. This change in flux linkage induces a current in the other wire wrapped around the other side. P1=P2. also V1/V2 = N1/N2 where N is number of coils.

53
Q

what is the equation and unit for magnetic flux linkage?

A

Ψ = NΦ = BAN

Wb turns

54
Q

what is the definition of Lenz’s Law?

A

the direction of induced EMF will oppose the direction of force that caused it

55
Q

what happens when a magnet is dropped through a wire?

A

magnet induces a current in the wire. current then produces a second magnetic field around the wire that opposes the motion of the magnet. forces balance so magnet travels at constant velocity. half way down direction of current and magnetic field switches to keep pushing the magnet back up

56
Q

what is stopping voltage and what is it equal to?

A

it is the voltage needed to stop current flowing in the other direction between the two plates. (photoelectric effect)
Vs= E/Q = (1/2 mv^2) /Q
Ek=eVs
where Ek is maximum kinetic energy and Vs is stopping voltage

57
Q

what does Φ represent in the photoelectric effect?

A

work function (minimum energy gained from an electron absorbing a photon to be released from the metal)

58
Q

what are the 4 ways that the particle theory of light supports the photoelectric effect?

A

particles would gain energy as each wave hits so doesn’t explain threshold frequency.

photoelectric effect is immediate whereas it takes time for waves to give energy.

increasing intensity doesn’t increase max KE but increases number of electrons emitted.

electrons are emitted with different Kinetic energies.

59
Q

what is potential in the context of grav/electrical potential?

A

force per unit mass/charge of a point in a field

60
Q

what does the time constant represent in capacitance?

A

time constant=RC
=time taken for capacitor to discharge to 37% or charge to 63% of its original value of voltage/ charge. (also works for current when charging)
1/e = 37%

61
Q

what is resonance?

A

when driving frequency is close to natural frequency meaning that energy is transferred to the system efficiently

62
Q

what are the notable points on a stress/strain graph?

A 
limit of proportionality: end of straight bit
elastic limit
yield point: first peak
ultimate tensile strength: second peak
breaking point: end of line
63
Q

what is faraday’s law and what does it mean?

A

e= -d/dt Nϕ

emf produced is directly proportional to rate of change of flux linkage

64
Q

what is the equation for force on charged particle in a magnetic field and what do the letters mean?

A 
F=bev
F: force
b: flux density
e: charge of particle
v: velocity of particle
65
Q

how to draw a field?

A

positive to negative lines with arrows and dotted equipotential lines

66
Q

what makes an idea gas?

A

all collisions are 100% elastic
no intermolecular forces meaning no potential energy
pV=NkT

67
Q

what is luminosity a type of and how does it relate to intensity?

A

luminosity is a type of power and luminosity/area = intensity

68
Q

how does Wein’s Law show that hotter black bodies have more energy?

A

temp inversely proportional to wavelength so proportional to frequency. E=hf so more temp -> higher frequency -> more energy

69
Q

what are some assumptions in thermodynamic questions?

A

gas behaves as ideal gas
volume/ mass/ number of molecules/ pressure/ temperature constant
temp of fluid is the same as the outside

70
Q

what is the difference between phase and path difference?

A

phase difference is how far ahead a wave is from another (measured in degrees or radians as a fraction of a wavelength)
path difference is difference is distance travelled

71
Q

what is a standing wave?

A

the superposition of two coherent waves that are travelling in opposite directions. no energy is transferred

72
Q

what are the three main features of a lens?

A

principle focus: the point where an image would be created if parallel light rays enter
focal length: distance from lens to principle focus
power: ability to bend light. converging have +ve value, diverging have -ve value

73
Q

what is a photon?

A

a discrete packet of electromagnetic energy

74
Q

what is the angle of parallax and a parsec?

A

parallax is angle between lines drawn from the earth to a near star when the earth is in front of the sun and a quarter way around. a parsec is the distance of this object when the parallax angle is one arcsecond (1/3600 th of a degree)

75
Q

what are standard candles?

A

objects of known luminosity whose distance can be calculated with I=L/4πd^2

76
Q

what is evidence for dark matter?

A

due to how centripetal force works, stars further from the universe’s centre should travel slower but they don’t. This means that they have extra mass that can’t be detected (dark matter)

77
Q

what is the difference between pions and muons?

A

pions are mesons made of a first-gen pair, muons have a strangness

78
Q

why are fusion reactions hard to contain?

A

high temperatures are needed to heat plasma. magnetic fields are needed to keep plasma off of the walls of the reactor or it will cool and the reaction stops.

79
Q

what is ionising radiation?

A

particles that remove electrons from atoms/molecules

80
Q

what characterises a damped simple harmonic motion system?

A

at least one external force is acting, causing the system to lose energy to the surroundings.

81
Q

what are the three ways of measuring distance in space?

A

parallax
standard candles
red shift and v=H₀d

82
Q

what direction do electric field lines go? which way is a positive/ negative force?

A

field lines are +ve to -ve. +ve force is repulsuve, -ve force is attractive

83
Q

what is field strength and potential?

A

strength: force per mass/charge at a point
potential: work done to move a point from infinity to a point

84
Q

what are equipotentials?

A

two points that have the same potential so when a mass/charge moves from one to the other, no work is done

85
Q

what is time constant equal to?

A

t=RC
= time taken to charge capacitor to (1- 1/e) of final value
= time taken to discharge capacitor to 1/e of initial value

A Level Mid Terms (6 decks)

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