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Physics/AP Flashcards

1
Q

what is a charged object and when is an object positively or negatively charged

A
  • a charged object is one which has gained or lost electrons
  • a negative object has gained electrons
  • a positive object has lost electrons
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2
Q

how can we charge insulators and why does this happen

A
  • insulators can be charged by friction, when two insulators are rubbed together their electron clouds interact and there is a transferal of electrons
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3
Q

what occurs due to this transferal of electrons in insulators

A
  • you get two equal and oppositely charged objects

- they don’t immediately discharge because electron movement in insulators is low

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4
Q

what are some dangers/problems with static electricity/charge and how do we prevent them

A
  • dirt can cling to statically charged monitors
  • refueling aircraft can be dangerous if a static charge builds up in the pipe used to transfer the fuel
  • we use earthing cables to carry the charge away to prevent this
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5
Q

what is the difference between ac and dc

A
  • DC is the constant flow of current in one direction, it is a constant voltage circuit
  • AC is the flow of electrical charge which periodically (sinusoidal) changes direction
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6
Q

what is the IV graph for a resistor and filament lamp

A

a resistor has a straight line where grad = 1/R

a filament lamp has -ve N^2 shape for a half curve where x>0 and +ve N^2 shape where x<0 for half a curve

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7
Q

how does this change with VI graphs

A

resistor = the same but gradient is R

filament lamp has increasing/decreasing gradient – opposite to IV

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8
Q

define a magnetic field and how we can detect one

A

“a magnetic field is a field surrounding a permanent magnet or current carrying conductor in which magnetic objects will experience a force”

  • we can detect them using a plotting compass
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9
Q

what to remember when using magnetic field lines to plot magnetic fields

A
  • lines go North Pole to South Pole
  • equally spaced = uniform field
  • closer lines = stronger field
  • strongest field usually at both poles
  • N-N and S-S repel
  • N-S and S-N attract
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10
Q

what happens when a conductor carries a current

A

a magnetic field is created around the wire

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11
Q

why does this field around a current carrying conductor occur and what is the difference to permanent magnets

A
  • electrons in the wire have a charge
  • when any charged particle moves it creates a magnetic field around it
  • in permanent magnets, it’s due to aligned fields around the nuclei of the atoms due to the electrons orbiting them
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12
Q

what does a magnetic field around a current carrying conductor look like and how can we remember it

A
  • for a current carrying conductor, the magnetic field lines are concentric circles at 90degrees to the wire
  • right hand rule = hold out your right hand as a thumbs up, the thumb is the direction of the conventional current and the fingers show the direction of the magnetic field lines around the wire
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13
Q

what does the magnetic field look like if its a long coil of wire (solenoid)

A
  • it occurs as straight evenly spaced lines within the coil (uniform field)
  • but then some lines loop back round to the other end
  • outside of the coil between poles it is also uniform
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14
Q

what is a magnetically hard material

A

one which can be permanently magnetised

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15
Q

what is a magnetically soft material

A

one which can only be temporarily magnetised

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16
Q

what is an induced magnet

A
  • an induced magnet only becomes magnetised when in a magnetic field
  • they can’t be repelled, only attracted by other magnets
  • they lose their magnetism once removed from the field
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17
Q

what are the factors on the strength of electromagnetism

A
  • number of loops in the electromagnet
  • adding/changing a metal core
  • current, a greater current = more electrons = stronger field
  • increasing wire size can decrease resistance so increase current
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18
Q

what occurs to a current carrying conductor when placed in an external magnetic field

A
  • it experiences a force as the magnetic field produced by the wire interacts with the external magnetic field
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19
Q

how can we remember the important bits about a CCC in an external field

A
  • Fleming’s left hand rule
  • use thumb, index finger and middle finger all at right angles
  • Mr Fleming’s Cat going down
  • i.e. Motion on thumb, external Field on index, Current on middle
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20
Q

what are the magnitudes of the forces experienced by the wire in comparison to the other magnets

A
  • the wire experiences a force of F

- the two magnets experience forces of F/2 each

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21
Q

what are the factors on the force experienced by a CCC in an external magnetic field and formula

A
  • B, the magnetic flux density of the field
  • I, the current in the wire
  • L, the length of the wire in the magnetic field
  • Sin(theta), the angle between the field and current direction

F = BILsin(theta)

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22
Q

what is this formula (know) when the angle between the current direction and field direction is 90 degrees

A

F = BIL

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23
Q

When is an EMF induced in a wire

A
  • when there is a change in magnetic flux (same as work function symbol)

M.F. = BAcos(theta)
flux linkage = M.F. x number of coils
EMF is directly proportional to rate of change of flux linkage

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24
Q

how can an AC be induced in a wire

A
  • repeatedly move a magnet towards and away from a wire wrapped around a core
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25
Q

what are the factors on the AC produced

A
  • number of coils in wire
  • speed of movement of magnet
  • rate of change of cutting magnetic field lines/ rate of change of flux linkage
  • length of conductor
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26
Q

how can a DC motor be produced

A
  • split ring with brushes delivering current
  • ring connected to split ring inside an external magnetic field
  • every half turn the current changes direction, this spins the ring
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27
Q

how to produce an AC motor

A
  • non-split ring with brushes delivering current connected to a ring placed in an external field
  • this means the ring only rotates a half turn before rotating back
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28
Q

How can we increase the force produced by the DC motor

A
  • increasing current
  • more coils
  • stronger magnet
  • less friction
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29
Q

name some uses of electromagnets

A
  • loudspeakers
  • transformers
  • MRI machines
  • motors etc.
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30
Q

what do transformers do

A
  • they use electromagnetic induction to change voltage
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31
Q

what is the formula of coils and voltage for an ideal transformer

A

Ns/Np = Vs/Vp

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32
Q

what is the formula for I and V for an ideal transformer

A

VpIp = VsIs

  • Because in theory all power is transferred (100% efficiency)
33
Q

what is thermal radiation

A

thermal radiation is EM waves in the IR region of the spectrum (usually)
- temp can change freq.

34
Q

what are the 4 factors on emission and absorption of thermal radiation

A
  • darker colours emit and absorb more radiation than light colours
  • a greater surface area increases the rate of absorption and emission
  • matte surfaces give a higher absorption and emission
  • temperature, the higher the temperature the greater the rate of IR emission
35
Q

what is the Doppler effect

A
  • As an object emitting a wave travels towards you, the waves become squashed, this decreases the wavelength
  • as it travels away from you the waves are stretched and the wavelength increases
36
Q

what is the equation for the Doppler effect

A 
FO = F1(V/V+-VS)
FO = freq for observer
F1 = freq for source
V = velocity of wave
VS = velocity of source
37
Q

what is a nuclide and give an example of different nuclides

A
  • A nuclide is an atom or species with a specific number of protons and neutrons in its nucleus
  • e.g. C12 is different to C13
38
Q

what determines how stable a nucleus is and what happens if its unstable

A
  • the balance of protons and neutrons

- if a nucleus is unstable it undergoes radioactive decay

39
Q

what are the two main features of radioactive decay

A
  • it’s spontaneous, cannot be sped up/slowed down and we can’t change it
  • it’s random, we don’t know when a particular nucleus will decay and each nucleus decays independently
40
Q

what is alpha radiation

A
  • 2 Protons and 2 Neutrons
  • He nucleus
  • it has a mass number of 4 and an atomic number of 2
  • has a 2+ charge
41
Q

what is Beta - radiation

A
  • a stream of fast moving electrons
  • formed when a neutron decays into a proton and an electron, has a mass number of 0 and an atomic number of -1 (in equations)
  • has a charge of -e
42
Q

what is beta + radiation

A
  • a stream of fast moving positrons
  • formed when a proton decays into a positron and a neutron
  • has a mass number of 0 and an atomic number of 1 (in equations)
  • has a charge of +e
43
Q

what is gamma radiation

A
  • high frequency EM radiation
44
Q

what is the relative penetrating power of the types of radiation

A
  • alpha = low = stopped by paper
  • Beta + or - = medium = stopped by aluminium
  • Gamma = High = stopped only partially by a lot of lead
45
Q

what are the relative ionising abilities of the types of radiation

A
  • Alpha = large mass/charge = high
  • Beta = low mass/charge = low
  • Gamma = negligible ionisation
46
Q

how do the different types of radiation deflect in a magnetic/electric field

A
  • gamma doesn’t
  • Alpha deflects slightly to negative
  • Beta + deflects lots to negative
  • Beta - deflects lots to positive
47
Q

what to remember about nuclear decay equations

A
  • EVERYTHING must be conserved

- if a neutron is fired at the start, don’t forget it from your mass equations

48
Q

what is background radiation and what causes it

A
  • it is radiation that is constantly around us

- it’s mostly caused by rocks, domestic gases, CMB

49
Q

what are the risks associated with ionising radiation

A
  • it can cause cell/DNA mutations
50
Q

what is a half life

A

“the half life of an isotope is the average length of time required for half the active nuclei in the sample to decay”

51
Q

what is the decay constant and the equation with it

A

it is the probability of decay of an individual nucleus per unit time (lambda)

A = Lambda x N
activity = decay constant x number of active nuclei
52
Q

what is the general equation for dealing with half lives

A

N = N0 x e^(-lamdba x t)

53
Q

how can the generalised equation be rearranged to include the half life

A

substitute in N0/2 for N
and T1/2 for t
this gives
lambda x t(1/2) = ln(2)

54
Q

what are decay products

A
  • when a nucleus starts decaying, some of its decay products will also decay
  • due to the nature of half lives, this can all occur simultaneously
55
Q

what to do if it has a non-100% efficient motor and energy loss elsewhere

A
  • if it asks for total energy loss then do

energy loss to surroundings + energy loss through efficiency = total energy loss

56
Q

what to do if the difference of two lengths is calculated questions

A
  • if asking displacement from centre point then half the difference between the two distances
57
Q

units for energy

A

kgm^2s^-2

E= MC^2

58
Q

units for force

A

kgms^-2

F= MA

59
Q

units for momentum

A

kgms^-1

60
Q

equation for voltage

A

V = IR

61
Q

3 equations for power

A 
P = IV
P = I^2 R
P = V^2/R
62
Q

equation for elastic potential energy

A

Ep = 1/2 kx^2

63
Q

equation for force vs extension

A

F = kx

64
Q

equation and proportionality for voltage against speed of an electron and what this actually means

A 
eV = 1/2 mc^2
thus v is prop to c^2
so
sqrt(voltage) = k c
e.g. if voltage x 1/2
c x 1/sqrt(2)
65
Q

equation for work done

A

w = fxcos(theta)

66
Q

which direction do resistive forces act on an inclined plane

A

parallel to the plane

67
Q

how does energy get transferred in liquids

A

through collisions of particles with different amounts of kinetic energy, not through vibrations, that is a solid

68
Q

which way does a wave bend when it enters a more optically dense medium

A

towards the normal

69
Q

what is the relationship between time and number of waves to give frequency and period

A

number/time = frequency

time/number = period

70
Q

how to solve suvat questions where they need to be at the same displacement i.e. where they meet at

A
  • form equations for both objects including any initial displacements (pick a start point)
  • remember negatives
  • set them equal and solve for whatever you need to
71
Q

how do circuits where you have 2 loops where the centre is a part of both loops and the batteries face in opposite directions work

A
  • use kirchoff’s laws of current to show that the centre has a current equal to that of both the outer loops
  • consider the outer loops separately
  • simultaneous equations may need to be used
72
Q

what are the relevant equations for calculating the pressure exerted by falling water onto a surface

A
  1. hydrostatic pressure
    hydrostatic pressure = density x gh
  2. other pressure
    f/a = deltaP/(deltaT x A)
    often in these cases, delta t we ignore
73
Q

what to remember when working with multiple springs connected in series with each other

A

if there is a mass attached to the top spring and the bottom spring
the top spring experiences both masses
the bottom spring only experiences one of them

74
Q

what is the angle of incidence and refraction in a longitudinal wave

A

take the angle between the lines representing the peaks and the region boundary, because of right angles and right angled triangles, this works

75
Q

can thermal radiation travel in a vacuum

A

yes

76
Q

is a shiny surface a good emitter of radiation

A

No

77
Q

if the mass of an object decreases at a constant rate and the force remains constant, what happens to the acceleration

A

it increases at an increasing rate, think of reciprocal graphs

78
Q

what 3 factors do we want for minimum rate of thermal conductance through a bar

A

longest distance/length
minimum diameter/radius
lowest temperature difference

79
Q

what are the useful equations for transformers

A 
VpIp = VsIs (where 100% efficiency)
Np/Ns = Vp/Vs
Is/Ip = Ns/Np

University Prep (6 decks)

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