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96 Cards in this Set
- Front
- Back
momentum
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Ft = mv-mu
F = (mv-mu)/t = m(v-u)/t = ma impulse = change in momentum |
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rebound momentum
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2mu only if the speed of impact is t equal to the speed of rebound
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momentum in an explosion
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total momentum is 0
when direction is taken account of |
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circular motion F=
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centripetal force
acting towards centre mv^2/r mω^2r |
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circular motion v=
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straight line velocity
2πr/T 2πrf ωr |
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angular speed w=
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amount of angle travelled per second
2πf 2π/T |
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centripetal acceleration a=
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the acceleration towards the centre of motion
v^2/r ω^2r |
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circular motion positive direction ?
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towards centre
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car on banked track v=
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v^2 = gr tanθ
(N+N)sinθ = mv^2/r (N+N)cosθ = mg (N+N)sinθ / (N+N)cosθ = v^2/rg tanθ = v^2/rg |
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amplitude
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maximum displacement from the equilibrium point
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Time period
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time to complete one full cycle (seconds)
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Frequency
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the amount of cycles/ oscillations in one second (Hz)
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phase difference
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2πΔt/T
must be in radians |
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simple harmonic motion
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acceleration is always opposite to direction of displacement
a = -kx a = -(2πf)^2 x undamped system |
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Time period / frequency of simple harmonic motion
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T = 2π sqrt(l/g)
T = 2π sqrt(m/k) |
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energy of simple harmonic motion
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total energy is always constant
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energy stored in a spring
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0.5kx^2
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resonance
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when the periodic force is applied at the natural frequency
phase difference of π/2 |
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Bartons pendulums
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target pendulum is in resonance π/2 out of phase
shorter π/2 out of phase longer π out of phase |
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radial field
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field lines like spokes on a wheel directed to the centre
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uniform field
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same magnitude and direction throughout the field
parallel field lines |
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gravitational potential
work = |
mass (m) x potential (v)
therefore potential is the work per unit mass or energy per unit mass |
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gravitational potential (v) unit
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J/kg
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gravitational field
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force per unit mass
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equipotential gradients
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lines where the potential of the field are equal
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potential gradient
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change of potential per metre at that point
Δv/Δr |
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connect g and V
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g is the gradient of v
therefore Δv/Δr = g |
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gravitational force
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F = G Mm/r^2
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gravitational field against distance
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g = GM/r^2 as long as r is larger than the radius of the body
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geostationary satellites
T = |
24 hours
86400 seconds |
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electric field direction
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positive to negative
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electric field vector or scaler
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vector
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electric field strength
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force per unit charge
E = F/Q |
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density of field lines show
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the strength of the field
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electric potential
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work done per unit charge to move it from infinity to that point in the field
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unit of electric potential
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Volt (v)
1 J/C |
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(electric) energy can be calculated as
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Voltage x charge
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electric potential and electric field strength connection
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the electric field is the gradient of the electric potential
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equipotential of electric fields
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can be a 0 point where there is no potential
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coulombs law
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F = k Qq/r^2
k = 1/4πε |
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electric field definition
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force per unit charge
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compare force of gravitational field and electric fields
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F = GMm/r^2 = Qq/4πεr^2
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compare field strength of gravitational field and electric fields
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g = F/m E = F/q
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compare units of gravitational field and electric fields
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N/kg or m/s^2
N/C or V/m |
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compare units of potential of gravitational field and electric fields
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J/kg Volts (J/C)
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radial gravitational field
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g = GM/r^2
v = -GM/r |
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radial electric field
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E = Q/4πεr^2
v = Q/4πεr |
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capacitor
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a device designed to store charge with two metal plates separated by an insulator
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charge on a capacitor
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charge = current x time
C = C/S x S |
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how to measure capacitance
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charge a capacitor through a variable resistor, by varying the resistance keep the current constant. Multiply the current by the time, plot charge against the voltage which is measured through a volt metre on the capacitor. to find the capacitance find the gradient Δq/Δv
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capacitance
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the charge stored per unit pd
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energy stored in a capacitor
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E = 0.5QV = 0.5CV^2 = 0.5(Q^2)/c
Area under a voltage charge graph |
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capacitor discharge
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Q = Qe^(-t/RC)
V = Ve^(-t/RC) I = Ie^(-t/RC) |
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Time constant
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RC
Resistance x capacitance |
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Capacitor charging
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the charge will go up making the resistance of the capacitor higher so the current will drop
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magnetic flux density
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B - strength of the magnetic field
force per unit length per unit current on a current carrying conductor at right angles to the magnetic field lines |
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flemings left hand rule
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thumb - force
index - field middle - current |
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force of a magnetic field
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F = bIl
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simple electric motor
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the current is in a different direction on both sides of the coil so the force is in different directions.
a split ring communicator is needed so the current will change direction on the sides of the wire to i will spin the same direction |
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unit of magnet it field B
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Tesla T or wb/ or NS/Cm
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magnetic flux
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magnetic flux density x area
BA |
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magnetic flux linkage
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magnetic flux density x area x number of coils
BAN |
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force on a moving charge
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F = BQv
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radius of charge in magnetic field
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BQv = mv^2 /r
r = mv/BQ |
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Thermionic emission
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heated metal will give of electrons
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what happens when a wire is moved in a magnetic field
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an emf is produced
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emf produced when ?
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when there is relative motion between the magnetic field and a conductor
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dynamo rule
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thumb - motion
index - field middle - induced current |
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lenz's law
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the direction of the induced current is always such as to oppose the change that causes the current
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Faradays law of electromagnetic induction
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induced emf in a circuit is equal to the rate of change of flux linkage through the circuit
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emf
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emf = -N ΔΦ/Δt
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transformer equation
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Np/Ns = Vp/Vs = Is/Ip
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how are transformers made more efficient
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core to make the field lines go through the second coil
laminated coil to reduce eddy currents |
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efficiency of a transformer
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IsVs/IpVp x 100
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grid system
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high voltage low amps
alternating current so magnetic field changes so transformers can be used |
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rutherford experiment
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alpha particles shot at gold foil (all same kinetic energy) 1 in 2000 are deflected
1 in 10000 deflected over 90 degrees nucleus contains most mass and is positively charged |
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gold foil in alpha scattering need's to be
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thin to stop double scattering and to let alpha particles through
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alpha particle in cloud chamber
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all easily visible and the same length showing they all have the same kinetic energy
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β particles in cloud chamber
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wispy tracks that are easily deflected by air molecules, not as easy to see because β particles are less ionising
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intensity of gamma source
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k/r^2
nhf/4πr^2 |
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activity of radioactive source
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number of nuclei that disintegrate per second
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unit of activity
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becquerel Bq
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alpha and beta emission on NZ graph
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alpha - looses two N, looses two P
Beta minus - Gains P, looses N Beta plus - looses P, Gains N |
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metastable state
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gamma photon must be emitted to get to ground state
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binding energy
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work that must be done to separate a nucleus into its constituent particles
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mass defect
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difference between the mass of separated nucleons and the nucleus
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internal energy
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sum of kinetic energy's and potential energy's of molecules
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Celsius - kelvin
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Celsius = kelvin - 273.15
Celsius + 273.15 = Kelvin |
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specific heat capacity Q =
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mcΔt
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specific heat capacity
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the amount of energy to raise the temperature of a unit mass by 1 kelvin without changing the state
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latent heat graph
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during phase change there is energy input but no heat change
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latent heat of fusion
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energy needed to melt a solid at it's melting point
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latent heat of vaporisation
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the energy needed to vaporise a liquid at it's boiling point
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specific latent heat of fusion
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energy needed to change the state of unit mass of a substance from solid to liquid without temperature change
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specific latent heat of vaporisation
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the energy needed to change the state of unit mass of a substance from liquid to vapour without change in in temperature
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kinetic theory temperature
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