revision cards Flashcards
define acceleration
Acceleration is the rate of change of velocity ie an acceleration of 5 ms-2 means the velocity is
increasing by 5 ms-1 every second
what are satelites
satelites are in freefall around a planet or star. They are constantly accelerating but not changing speed. this is because of direction, not the magnitude of their velocity is changing. the surface of the planet or star curves away from the satellite at the same rate the satelite curves towards it hence the satelite remains in orbit at a constant altitude
what are the rules for projectiles
o The first job is usually to resolve the initial velocity into components (uhorizontal = u cosθ and
uvertical = u sinθ where θ is the angle to the horizontal)
o From now on only use the components uh and uv
o Horizontal velocity is constant (use sh = vh t)
o Vertical acceleration is constant due to gravity (use sv uv vv av t and watch your negatives).
define newtons first law
newtons first law states that an object will remain at rest or move with a constant speen in a straight line (constant velocity) unless acted upon by an unbalanced force
newtons second law
F = ma.
newtons third law
states that for every action there is an opposite and equal reaction. punch a wall and the force of my fist on the wall is equal to that of the wall on my fist
friction
force that always acts opposite to an objects motion
tension
pulling force, acts both ways at same time
air resistance
increases with speed. what makes an object eventually reach terminal velocity
scales in a lift
scales measure the force acting upwards on a person
slopes
The component of weight acting down a slope = m g sinθ where θ is the angle of the slope
to the horizontal.
define the conservation of momentum
states that the total momentum before a
collision/explosion is equal to the total momentum after the collision/explosion as long as no
external forces are acting
what is an elastic collision vs an inelastic collision
Elastic collision: Kinetic energy is conserved. Inelastic collision: Kinetic energy is NOT conserved.
in both momentum is conserved
impulse
the change in momentum = area under a force time graph. this takes place when there is a net external force. Ns
gravity Qs
remember to measure from center of one mass to center of the other
relativity - what is time dialation and length contraction
The speed of light in a vacuum is the same for all observers.
Time dilation is the increase in an observed time interval for an object moving relative to an
observer compared to that measured when they are in the stationary frame of reference.
Length contraction is the decrease in the observed length (in the direction of motion) of an object
moving relative to an observer compared to that measured when they are in the stationary frame
of reference.
t and l are when the observer and object are stationary relative to each other, ie they are in the
same location, and t’ and l’ are when there is relative motion, ie things are observed in more than
one location.
Evidence supporting the Big Bang/expanding universe theory
Cosmic Microwave Background Radiation
the abundance of hydrogen and helium
the darkness of the sky (Olbers’ paradox) - if universe infinite should be stars in all parts of the night sky
the large number of galaxies showing redshift rather than blueshift.
dark matter
the mass of a galaxy can be estimated using the orbital speed of their stars
Masses measured are bigger than those predicted by looking at the number of stars present
conclusion is that there must be matter we cant see - Dark matter
Dark energy
supported by the accelerating rate of expansion of the universe ie something appears to be opposing gravity
hotter the star is the
shorter the peak wavelength of emitted radiation (more blue)
the more energy it emits per m^2
what is the longest and shortest wavelengths of visible light and what colours do they appear as
380 - 700 nm
380 is violet and 700 is red
Standard Model
12 Fermions (matter particles)
6 Quarks – up, down, charm, strange, top, bottom
6 Leptons – electron, electron neutrino, muon, muon neutrino, tau, tau neutrino
4 Gauge Bosons (force carriers)
photon (electromagnetic force)
Z and W± bosons (weak nuclear force)
gluon (strong nuclear force)
Hadrons
made up of quarks
Baryons are made of 3 quarks eg protons, neutrons
Mesons are made of 2 quarks (a quark and an anti-quark) eg pions, kaons
strong force
Strong force holds quarks together and also holds protons and neutrons together in the nucleus
beta decay
Beta decay is caused by the weak force and is evidence of the Neutrino
beta minus decay consists of a neutron is affected by the weak force and one of its down quarks turns into an up quark becoming a proton . to conserve charge an electron is emitted aswell as an anti neutrino
beta plus decay - proton affected by the weak force turns into a neutron (up quark turns to down quark). releasing an anti electron (positron) and a nuetrino
what is antimatter
particles are identical to their corresponding matter particles except charge. if touches its matter counterpart it is annihalated
Eletric field - what way do lines go , what particles will accelerqte and why
in diagram lines point from pos to neg
a charged particle will accelerate in an eletric field because it experiences unbalanced forces
gain in kinetic energy = work done by eletric field
what is p.d.
voltage is the number of joules of energy per coulomb of charge
magnetic feilds - what does moving a charged particle do, which way do field lines go
moving charged particle will produce magnetic field
field lines point from north to south
what is nuclear fusion
nuclear fusion is smaller parts combining to a more massive nucleus
whatever mass is not converted is turned into E ——- E=mc^2
what is fission
big nucleus splitting into smaller parts
induced/stimulated - usually caused by bombardment with nuetrons
spontaneous - random event/no trigger
wave particle duality
the photoelectric effect is proof that light is a particle
interference proves light is a wave
photoelectric effect
clean negatively charged zinc plate exposed to high F ultra violet light discharges
each photon of light gives electron energy to jump off
light going from vacuum (air) to medium
speed wavelength and angle all decrease
F does not change
total internal reflection occurs when
the angle of incidence is greater than the critical angle
irradiance from a point scource follows what law
inverse square law
if you double the distance then the irradiance will quarter
if you triple the distance then the irradiance will be 9 times less
bohr model of atom
Eo is the ground state and lowest E level
E0, E1, E2 etc have negative energy levels in comparison to the ionisation level
‘
ionisation level has an energy of 0 - if electron gain ionisation energy they jump off
electrons gain E and jump up if they go down E they give off photon of light
peak and rms
peak always bigger rms = peak over root 2
use rms values for power calc
parallel and circuit
o Current in series is the same (CISS), current in parallel branches add up to supply current
o Voltage in parallel is the same, voltage in across series components add up to supply voltage
(VIPs use VISA …)
t.p.d. = terminal potential difference
the p.d across the rest of the circuit
ideal supplu
A SUPPLY with no r
open circuit
infinite resistance - nothing connected across terminal
supply = emf as no current so no internal resistance
short circuit
no load resistance and mac current drawn
how is r calculated
use a variable resistor and plot V on y and I on x
r = negative gradient
emf = y intercept
max current = x intercept
if more than one supply
combine rs and emfs
capacitance is
the number of charge stored per volt
charge against p.d. graph
Gradient = capacitance
area under the graph = energy stored
when capacitor is fully charged
p.d = supply V
current = zero
V across resistor = 0
when Capacitor is fully discharged
V = 0
Current = max current allowed by ohms law
V across R = supply V
Current does what when charging AND discharging
starts large and decreases in magnitude
Increasing R or C does what
increases the time taken for capacitor to charge and decreases magnitude of max current
increasing C also increases the max energy stored(can also be achieved by increasing supply voltage )
when atoms combine what happens to the electrons
they combine into energy bands instead of discrete energy levels
what are the diffs between the bands
the fullest band is the valence band and the band above that is the conduction band.
electrons are held tightly in the valence band but have room to move freely in th econduction band.
conductors
have overlapping conduction and valence band so dont require energy for electrons to move across bands
insulators
have a empty conduction band and an full valence band
there is also a large energy gap so the electrons require large amounts of energy to jump up
what is doping
adding impurities to semiconductors to reduce their resistance
what is a semiconductor
like an insulator but with a much smaller band gap, the gap is small enough that at room temperature some electrons have energy to jump from valence to conduction band and increase the conductivity of the solid. conductivity increases aka resistance decreases with increasing temperature
n-type
an n-type semi conductor is one that has been doped with an element with more electrons so there are extra electrons. these are added to the conduction band and allows it to conduct more. makes it negative
p-type
impurities are added which have extra holes.
this creates gaps in the valence band. this makes it p
p-n junction
p and n type conductors are side by side. a depletion layer forms which has virtually no free charge carriers.
forward and reverse biased
forward = n to negative and p to positive
reverser means opposite
solar vell
is an unbiased p-n junction. photons enter and give electrons enough energy to jump from valence band of p type to conduction band.
moves down to the n-type and a voltage is produced. this is the photo voltaic effect
Mrs Lindsay’s equation
Vr = (Rr/Rt.)xVo
