1
Q
gravity
A
acceleration of freefall due to Earth’s gravitational field
2
Q
Viscous drag/fluid resistance
A
Fluids oppose the motion of bodies passing through them as a frictional force F
3
Q
Bernoulli’s principle
A
for a fluid in motion, an increase in its speed occurs simultaneously with a decrease in its pressure
4
Q
Range formula not in data book
A
Sx=Ux * t
5
Q
Newton’s 3 laws of motion
A
1: every object will remain at rest or at constant speed in a straight line unless a resultant force acts on it.
2: F=ma. resultant force is proportional to the rate of change of momentum
3: for every action, there is an equal and opposite reaction
6
Q
Inertia
A
Reluctance of a stationary object to move
7
Q
grav. field strength
A
force per unit mass acting on a test mass
8
Q
conservation of linear momentum
A
in any collision or explosion, for an isolated system with no external forces acting, the total momentum before the collision is equal to the total momentum after the collision
9
Q
archimedes principle:
A
an object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.
10
Q
temperature:
A
measure of the average kinetic energy of the random motion of molecules of a substance
11
Q
Black body radiation
A
perfect absorber and emitter of radiation. does not reflect and emits a continuous range of wavelengths per unit area at 90deg.
12
Q
specific heat capacity
A
the heat energy needed to increase 1kg of a body by 1celsius
13
Q
specific latent heat
A
amount of energy needed to change the state of 1kg of a substance without changing its temperature
14
Q
during a change in state (4points)
A
-temp remains constant
- KE of molecules constant
- Heat energy is absorbed to weaken and or break bonds between molecules and increase separation
- PE increases, internal energy increases
15
Q
internal energy
A
total intermolecular potential energy arising from the forces between the molecules plus the total random KE of the molecules arising from the random motion
16
Q
albedo
A
the fraction of solar radiation that is reflected back into space by the planet
17
Q
absorption of infrared radiation by greenhouse gas molecules
A
The vibrational and rotational modes of the molecules have a natural frequency. Outgoing infrared radiation emitted from Earth has the same natural frequency. This causes the molecules to absorb the infrared energy and reradiate and oscillate at greater amplitude. The molecules internal energy increases and they reradiate this energy in all directions including down.
18
Q
What are the greenhouse gases
A
Methane CH4, Water H2O, Carbon dioxide CO2, Nitrous Oxide N2O
19
Q
Energy balance climate model (topic B)
A
see notes.
20
Q
kinetic theory of ideal gases
A
- no forces of attraction
- collisions are elastic (KE preserved)
- volume of molecules small compared to volume of gas
21
Q
Boyle’s law
A
for a fixed mass of gas at constant temperature, pressure is inversely proportional to volume. P1V1 = P2V2
22
Q
Charle’s law
A
for a fixed mass of gas at constant pressure, the volume is proportional to the Kelvin temperature V1/T1 = V2/T2
23
Q
Gay-Lussauc’s Law
A
for a fixed mass of gas ar constant volume, pressure is proportional to the Kelvin temperature. P1/T1 = P2/T2
24
Q
what happens to the work if there is no change in temp. and the volume remains the same? (gas)
A
no work done by expansion of the gas, and no work done on compression of the gas
25
negative and positive work
work done on a system is negative, work done by a system is positive
26
1st law of thermodynamics
energy can't be created or destroyed. the heat energy supplied to a system is equal to the change in internal energy plus the work done by that system
27
isothermal
pressure and volume change at constant temperature. Isothermal expansion: Q = W. Isothermal compression: -W = -Q
28
for isothermal change
slow change, thin walls, large surroundings
29
adiabatic
no heat enters or leaves.
adiabatic expansion: W = - delta U
adiabatic compression: - W = delta U
30
for adiabatic change
thick walls poor conducted cylinder rapid change
31
isovolumetric
constant volume, no work done.if decreasing pressure, therefore cooling gas both work and heat energy are negative.
32
isobaric
constant pressure. all positive for expansion, all negative for compression.
33
2nd law of thermodynamics
100% efficiency is impossible for a cyclic heat engine
34
Clausius statement for 2nd law
thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temp.
35
Kelvin statement of 2nd law
Heat energy cannot be extracted from a hot body and transferred completely into work
36
entropy in terms of 2nd law
the entropy of the universe is always increasing.
37
electric current
rate of flow of charge
38
how is a current produced
when a potential difference or voltage is applied across the ends of a conductor, the electrons are subject to an electric field., this force will be superimposed on top of the random motion of the electrons producing a current
39
potential difference
work done per unit charge to move a positive charge between 2 points along the path of the current
40
ohm's law
current is proportional to p.d. at constant temperature
41
simple harmonic motion
the acceleration of an oscillating body is directly proportional to its displacement from an equilibrium position (fixed centre point) and always directly towards that point (time period remains constant independent of amplitude).
when x =0, v= max, a = 0
when x = max, v= 0, a= -max
when x= 0, KE=max
42
Huygen's principle
every point on a wavefront acts as a source of secondary wavelets that move forward with wave velocity
43
when gapsize bigger than wavelength in diffraction,
small, no diffraction
44
when gapsize close to size of wavelength in diffraction,
big diffraction
45
critical angle
angle of incidence that results in an angle of refraction of 90 deg
46
total internal reflection
when the angle of incidence is greater than the critical angle
47
(young's double slit): fringe separation increases with)
- longer wavelength
- longer distance to screen (D)
- small source separation d
48
young's double slit meanings formulas
theta is for maximum, nwavelength=dsintheta
49
young's single slit meanings formulas
theta is for minimum, theta = nwavelnegth/b for other orders
50
the addition of further slits at same slit separation means:
- maxima have the same separation
- maxima become sharper
- more light let through -> intensity of interference pattern increases
51
standing waves
store energy, particles have different amplitudes. At a node N particles have zero displacement and at antinode A, particles have maximum displacement. within a loop, all particles oscillate out of phase to each other.
52
transverse waves
- transfers energy, all particles have the same amplitude but at different times. within a loop, all particles oscillate in phase (180deg), with the next loop.
53
formation of a standing wave
an incident wave hits a wall and it reflects back with 180 deg phase change. the two waves superimpose in many places and if boundary conditions are suitable, constructive and destructive interference can occur and a standing wave is formed.
54
resonance
when a system is forced to oscillate at its natural frequency and maximum amplitude
55
conservation of energy and damped oscillating systems
since energy cannot be created or destroyed, forced oscillations addd energy to the system. But, if this is not at the resonant frequency, the system would not undergo SHM, and energy would be converted to heat energy. eg child swing
56
moving source towards observer
observed frequency: f' =[ v/ (v-u) ] f
57
moving source away from observer
observed frequency: f' =[ v/ (v+u) ] f
58
moving observer towards source
observed frequency: f' =[ (v+u)/v ] f
59
moving observer away from source
observed frequency: f' =[ (v-u)/v ] f
60
gravitational field strength
force per unit mass acting on a test mass
61
newtons law of gravitation
there is an attractive force between all masses in the universe. the magnitude of the attractive force is proportional to the product of the masses and inversely proportional to the squared distance between them
62
Kepler's laws
1: planets orbit in elliptical orbits around the sun with the sun at one focus.
2: the line connecting the planet to the Sun sweeps out equal area in equal time
3: the square of the orbital period of a planet is directly proportional to the cube of the distance from the Sun to the orbit.
63
what is potential at a point in a gravitational field?
the work done per unit mass to move a test mass from infinity to that point
64
work done towards/away from a planet
work done by a mass moving away from a planet is +, work done by a mass moving towards a planet is -, work done by a gravitational force is the opposite.
65
gravitational potential energy
the work done to assemble the system from infinite separation of the components of the system
66
electric field/electric field strength
electric field: a place where a charge experiences a force
electric field strength: force per unit charge on a positive test charge
67
electric potential energy, change in electric potential energy and electric potential difference
electric potential energy: energy of a charge due to its position on an electric field.
change in electric potential energy: the work done needed to move a test charge between 2 points in an electric field
electric potential difference: difference in potential between 2 points in an electric field
68
electronvolt
the work done on an electron when it is accelerated by a potential difference of 1 volt Ve= 1/2mvˆ2
69
magnetic field in a single wire
right hand grip rule #1:
thumb is conventional current, fingers are magnetic field N to S
70
magnetic field in a solenoid (coil)
right hand grip rule #2:
thumb points to North Pole of coil, fingers are conventional current
71
to increase strength of magnetic field
more turns of wire, increase current
72
Magnetic field strength (B)/ magnetic flux density
the force acting per current length
units TESLA
73
EM induction moving single wire
Fleming's right (FBI), to predict inducced emf or current
74
how is induced emf produced
movement of conductor or magnet + magnetism, the conductor cuts the magnetic field lines
75
Lenz's law
the direction of the induced emf is such to oppose the change causing it
76
a coil moving through a magnetic field
Fleming's right hand (FBI), induced emf only when coil is moving in or out of magnetic field, but not when it is entirely in magnetic field as sides cancel out. but if constant velocity, no net force.
77
magnetic flux
product of the magnetic field strength and a perpendicular area
78
magnetic flux linkage
product of the number of turns of a coil (N) and magnetic flux
79
faraday's law
the induced emf is proportional to the rate of change of magnetic flux linkage
80
isotope
same number of protons, different number of neutrons
81
Rutherford experiment alpha particles proved that + explanation
proved that the nucleus is small, dense and positive and that the atom is mostly a vacuum.
- most alpha particles passed through the gold foil, some passed through with a small deflection, very small number of them were scattered over 90deg
82
limitations of the orbiting electrons atomic model
as moving charges, orbiting electrons should radiate EM waves, therefore losing energy and spiraling down into the nucleus, thus collapsing matter BIG NOPE. -> Bohr model: electrons have allowed energy states where they don't radiate energy
83
Quanta
smallest amount of physical quantity
84
atomic spectra the works
electrons gain energy from incident photons to move to a higher energy level, and cause the emission of a photon when they fall from an excited level to a lower level closer to the nucleus. spectra show that light and other EM radiation are not continuous waves but a stream of discrete photons. The greater the frequency of the photon, the greater the energy emitted/absorbed -> the bigger the fall between energy levels, greater the frequency
85
what different electron transitions result in
electron transitions that end in the Ground state (n=1), result in UV photons, transitions that end in n=2 result in visible light photons, transitions ending in n=3 or above result in infrared photons.
86
strong nuclear force
attractive but short range, counteracts the repulsive electric force between the protons to hold the nucleus together.
87
electromagnetic force
responsible for magnetic forces, attractive or repulsive depending on the signs of the charges. far exceeds gravity on the atomic scale. affects only protons, not neutrons
88
nuclear density
all nuclei have the same nuclear density independent of nuclear number -> 2.3x10ˆ-17
89
bohr model of the atom
there is an electric/Coulomb force between protons in the nucleus and orbiting electrons which provides the centripetal force. Therefore the electrons have KE, PE and TE and like planets, further from the nucleus, KE decreases while PE and ET increase (because the electron is attracted to the nucleus so PE becomes less negative)
90
problem with Bohr model +bohr's comeback
problem: since the electron is moving, it should radiate EM radiation but that doesn't happen (it would spiral down and collapse onto itself)
Bohr says this doesn't happen because:
- electrons are only found in discrete energy levels where they do not radiate energy
- when electrons move between energy levels they emit/absorb a quantum/photon os EM radiation
- in any one energy level, the angular momentum of the electron is quantized in internal values of h/2pi
91
Limitations with the Bohr model
- fails for atoms with 2 or more electrons (so only works for hydrogen) well done Bohr
- can't account why some electron transitions occur more than others
- doesn't explain WHY electrons don't radiate energy in discrete energy levels
92
stopping potential
reverse voltage required to stop the most energetic electrons from reaching the anode in a vacuum tube
93
work function:
photon energy required to eject an electron with 0 KE
94
photoelectric effect
incident light consists of particle like photons, each energy E=hf, one photon transfers all of its energy to one electron, to allow it to escape from the surface of the metal. If the incident photon has more energy than the minimum value needed for the electron to escape, the excess becomes KE of the electron.
95
binding energy
work done against the strong nuclear force to separate a nucleus into its constituent protons and neutrons
96
energy equivalent of one atomic mass unit (1u)
931.5 MeV
97
alpha properties
highly ionizing, stopped by paper, discrete, slow, deflected by both E fields and B fields
98
beta properites
ionising, stopped by few mm of aluminium, continuous, relevant speed, deflected by both E fields and B fields but in opposite direction to alpha
99
Gamma properties
weakly ionising, cm of lead, discrete, fast(speed of light), undeflected
100
antiparticles
to follow the laws of conservation of momentum, the rest of the energy is carried by the antineutrino.
has the same mass but opposite charge as a particle. If they meet, they annihilate each other, and their mass and KE are converted into Gamma ray photons.
101
Activity (decay)
-number of radioactive emissions per second.
- proportional to the number of nuclei of that sample at that time
102
critical mass
mass of nuclear fuel needed for self sustaining chain reaction. masses that are subcritical will stop, because neutrons escape.
103
advantages of nuclear energy
no CO2, high energy density, large reserves, cheap to run
104
disadvantages of nuclear energy
nuclear waste (very radioactive), very expensive to build, if there is a problem -> BIG PROBLEM
105
1 light year in metres
9.5 x 10ˆ15m
106
The sun temperature and pressure conditions
High temperature: H nuclei travel very fast to overcome electrostatic repulsion, greater number of collisions per second
High pressure: more nuclei per unit volume and greater chance of collisions.
107
parallax
the apparent movement of an object due to the movement of the observer.
108
stellar parallax
to measure the distance to stars, astronomers use the largest baseline possible which is the Earth's orbit. they take a picture of a star, wait six months until the Earth is on the opposite side of the Sun, and take another picture (2p)
109
parallax angle
half of the total angular shift observed. The closer the star, the larger the shift
110
Parsec:
distance at which a star would have a parallax angle of one arc second.
111
main sequence stars
like the sun, nuclear fusion of hydrogen
112
Red giants
eg. Betelgeuse
large, cool red starts at a later stage of life than main sequence. Fuse elements higher than Hydrogen
113
White dwarf:
- too small to see with naked eye
small, hot remains of a red giant when fusion has stopped happening and they are calling down -> when cooled down sufficiently, no light is emitted and we have a black dwarf
114
Neutron stars
- (pulsars)
Remains of a large star after a supernova. Very small, no fusion, very dense, made of neutrons
115
Hertzsprung-Russel diagram
- 90% of stars are in main sequence
- on main sequence, more massive stars are brighter and use up their hydrogen fuel faster
116
star formation
1: clouds of hydrogen gas and dust experience a 'kick' eg. supernova shockwave, and start collapsing under their own gravity
2: the central ball of gas gets increasingly hotter due to the friction of all the atoms being squeezed together -> protostar (not star yet)
3: core temperature reaches 10MK, and the core has reached a high enough density (more protons in less volume) and nuclear fusion begins -> H atoms slam together to form He.
4: Stable star is born -> produces its own energy. The inward gravitational force is balanced by the outward force due to nuclear fusion
117
why do stars of great mass have a shorter lifetime?
because they need a larger radiation pressure to resist the gravitational force therefore fusion takes place at a greater rate to produce higher core temps. and prevent collapse.
118
what does the stability of stars depend on?
on an equilibrium between outward radiation pressure and inwards gravitational forces
119
very low mass star evolutionary path
nuclear reactions stop, core remains as Helium
120
low mass star evolutionary path
main sequence -> Red Giant -> white dwarf surrounded by rings of planetary nebula
121
high mass star evolutionary path
main sequence -> super Red Giant -> supernova (colossal explosion of star) -> neutron star
122
very high mass star evolutionary path
main sequence -> super Red Giant -> supernova (colossal explosion of star) ->black hole.
123
Chandrasekhar limit
maximum mass that a stable white dwarf can have which is 1.4 times the mass of the Sun
124
oppenheimer-volkoff limit
maximum mass for neutron stars 1.5 to 3.0 times the mass of the Sun. above this, neutron degeneracy pressure can't resist gravitation and a collapse occurs which could result in a black hole.
125
Fusion after main sequence
H runs out -> core contracts due to less radiation pressure and temperature increases -> fusion of He into carbon and oxygen -> Fusion will stop when Iron is produced since it has the greatest binding energy per nucleon.
