Year 2 - A level Flashcards
What are the two parts of internal energy of molecules?
- Potential energy due to electrostatic attraction
- KE due to movement
Why can’t a body possess heat energy?
Heating is energy in transit from hot to cold regions.
Brownian motion
- Jerky, random motion
- Large smoke particles collide randomly with invisible air particles
Diffusion
Spread of gas or liquid in space provided.
What is Boyle’s Law?
For a fixed mass of gas at constant temp. pressure is inversely proportional to its volume.
Explain kinetic theory and pressure.
-Molecules hit container, require force change momentum and rebound.
-Newton 3rd, equal and opposite force on wall.
-Force increases, collisions faster and more frequent. Both increase with speed.
Therfore, KE molecules is directly proportional to temp.
What is Charles’ Law?
For a fixed mass of gas at constant pressure, volume is directly proportional to its absolute (kelvin) temperature.
What is the pressure Law?
For a fixed mass of gas at constant volume, pressure is directly proportional to Kelvin temperature.
What is the equation with p1 v1 and t1?
(P1V1)/T1 = (P2V2)/T2
What unit is temperature measured in?
Kelvin 0K = -273 degrees C
What is the ideal gas equation?
pV = nRT
KE theory 1.
What is change of momentum of particle m,cx as it hits wall x? What is the time between impacts on wall x over distnace L?
- Change in momentum = m(-cx) x mcx = -2mcx.
2. t = 2L/cx - between wall x collisions is two lengths
KE theory 2.
What is the force on the particle? and therefore the wall?
Change in momentum / time = -mcx^2/L
Newton’s 3rd means wall is +mcx^2/L
KE theory 3.
What is the pressure of 1 molecule?
Force / area. mcx^2/L^3 = mcx^2/V
Assuming N molecules what is the equation for pressure?
pV = 1/3Nmc^2 - 1/3 move perpendicular to each side.
As Nm is total mass p = 1/3ρc^2
How do you find (root mean squared speed)?
Square all speeds, find their mean, square root all
What are the 5 assumptions of ideal gases?
- No inter particle forces - All KE
- All collisions with wall perfectly elastic
- Obey Newton’s Laws
- Time during collision is negligible
- Molecules occupy zero volume
What are the ideal gas eqn’s from theory and expt?
Theory: pV =1/3Nmc^2
Expt: pV = nRT
Therefore, RT = 1/3Nmc^2
What is boltzmann’s constant in terms of R and NvA
k = Univ. gas constant / avagadro
What is mean KE of a molecule and therfore a mole?
KE of molecule = 3KT/2 and of a mole 3RT/2
At given temp what do all molecules have?
Same KE.
What links rms speed and temp?
Root of temp is proportional to rms speed.
What is a fixed point?
A point such as the boiling point of water which can be used to calibrate two thermometers.
Why do objects move in a cirlce?
Due to a resultant force acting towards the centre of the circle.
What is the equation for centripetal acceleration?
a = v^2/r = rω^2, assuming t and theta are small
What is the equation for centripetal force?
F = ma = (mv^2)/r = mrω^2
What is angular velocity? and the equation
The velocity of something spinning. ω = v/r = 2π/T = θ/t. rads-1
What is the definition of an electric field?
A region where a charged particle will experience a force.
What are the two shapes of electric fields?
Point charge - forms radial charge arrows show direction positive charge would move, weaker further from point.
Parallel plates - uniform field, equally spaced lines, equal strength.
What is the equation for electric field strength, force and charge? (uniform)
Electric field strength = Force / charge
What is coulomb’s law equation? (radial)
Force between = k Qq/r^2
What shows if a force is repulsive or attractive/
the symbol. - means attractive, + means repulsive
What are equipotentials?
Lines that join points of equal potential. At right angles to the field, indicate how fast a particle might accelerate.
What is the equation linking Electric field strength, voltage and distance? (uniform)
Electric field strength = Voltage / distance
What is an equation for electric field strength in radial fields?
E.F.S = k Q/ r^2
What is an equation for potential in a radial field? (electric)
V = k Q/r
What is a capacitor/
Two plates separated by an insulator used to store charge. The amount of charge stored is in capacitance ‘C’ measured in Farads.
What equation links charge, voltage and capacitance?
Q = VC
What do capacitors in series have in common?
The same amount of charge flows across them all. Therefore, two with different capacitance will have different voltages across them to keep charge the same
What equation links energy stored by a capacitor, voltage and charge?
Energy stored = 1/2 VQ.
Can use Q=VC rearranged to replace V or Q.
What is thermionic emission?
The release of electrons pfrom metal’s surface due to it being hot.
What equation links potential, work done and charge in uniform electric field/
V = W/Q
For discharging capacitors, what equation links charge, initial charge, time, resistance and capacitance?
Q = Qo e^-t/RC
For discharging capacitors, what equation links current, initial current, time, resistance and capacitance?
I = Io e^-t/RC
For discharging capacitors, what equation links voltage, initial voltage, time, resistance and capacitance?
V = Vo e^-t/RC
What is time constant?
The resistance x capacitance. The V, I or Q will have fallen to 1/e after 2RC it will be 1/e^2.
After how many time constants are capacitors said to be fully charged or discharged?
5RC as 1/e^5 < 1%
What is the definition of gravitational field strength/
Force per unit mass. g = F/M
What is the equation for force in gravitational field?
F= GMm/r^2
What does G stand for?
Universal gravitational constant. 6.672x10^-11 Nm2Kg-2
When is the only time you can use GPE = mgh?
In uniform fields close to the Earth surface (few km at most)
What is the equation for grav. field strength using G, mass and radius?
g = -GMe/r^2
Negative means attractive force.
What is gravitational potential?
The work done moving 1kg from point of 0 potential to a point in the field. Always negative, lowest potential at surface.
What is the equation linking grav. potential with G, m and r?
V = -GM/r
What links potential, WD and mass
V = WD/m
What links GPE, potential and mass?
GPE = Vxm = -GMm/r
What does the gradient of a grav. potential against radius graph show?
Line is below x axis. Gradient is g.
What two equations equal force for objects in orbits/
GMm/r^2 = mv^2/r
What is escape velocity? and the equation?
The velocity needed to escape the Earth’s gravitational field. Change in KE = gain in GPE = WD.
v= √(2Gm/r)
What might affect grav. field strength on Earth?
- Shape. g pole > g equator
- Type of rock. More dense = higher g.
- Rotation of Earth. Less g at equator as some of g is providing Centripetal acceleration.
What are Keplar’s Laws?
- Orbit of a planet is an ellipse with sun at one focus.
- The area of each section is the same time
- T^2 is proportional to r^3
What links v max, r/A and w
Vmax = rw
What is the definition of Simple Harmonic Motion?
Motion of a body whose acceleration is directed towards a fixed point (equilibrium) and is proportional to distance from that point.
What is true of time period?
Time period is constant and independent of amplitude.
What links accleration, angular velocity and displacment?
a = -w^2x
What does the graph of acceleration against displacement look like?
y = -x graph above and below axis.
What does SMH require? and what is the equation
A restoring force F = -kx
What is time period equation for a pendulum?
T = 2π√(L/g) with l as length of string and g as gravity
What is time period equation for a mass on a spring
T = 2π√(m/k) with k as spring constant and m as mass
What equation links angular velocity time and angle/
w = θ/t and 2π/T
What equation links x, A, w and t?
x = Acos(wt)
What equation links v, A, w and t?
v = -Aw sin(wt)
What equation links a, A, w and t?
a = -Aw^2 cos(wt)
What is total energy?
Kinetic energy and GPE continual transfer between these when oscillating
What is resonance?
Creating maximum amplitude oscillations. When forcing frequency = natural frequency.
What is damping?
Removing energy(amplitude) from a system. Usually as heat, frequency does not change
What does a graph of critical damping look like? and overdamped and lightly damped systems
Critical damping - curve returns to equlibrium. 0 on y axis.
Overdamped - Doesn’t return to eq.
Light (Exponential) damping - oscillates and amplitudes form exponential curve.
What is the equation linking amplitude, decay constant and time?
A = A0 e^-λt
Name a natural and artificial damper?
Natural - air resistance
Artificial - shock absorber
What does a resonance frequency graph look like with and without a graph?
Steep curve without damping, flatter wider curve with damping as less energy transfer.
Where would we use light or critical damping?
- Light to keep resonance in e.g. Pendulum clock.
- Critical damping to remove resonance e.g. bridges, cars
Explain an-echoic chambers.
Ductile foam cones can deform a lot before breaking = energy transfer to heat.
What size are the atom and nucleus?
Atom - 10^-10m
Nucleus - 10^-15m
What are atomic mass unit and eV in standard units?
u = 1.66x10^-27 kg eV = 1.6x10^-19 J
What links energy, mass and speed of light?
E = mc^2
What is binding energy?
The energy needed to separate the nucleus into its nucleons.
What is the equation for mass defect?
Mass defect = mass of nucleons - mass of nucleus
What is the most stable element?
Iron
Why do fission and fusion create more stable elements?
Energy is released
What is an enegy level?
A discrete energy of an electron
What is nuclear fusion?
Combining two lighter nuclei to get a heavier one and release energy (gamma photons and neutrinos)
What does fusion require?
- V high temps
- High densities and pressures (to overcome electrostatic repulsion)
What is nuclear fission?
Splitting a heavy nucleus into lighter nuclei, releasing energy. (Fire a neutron at it)
Name a problem and benefit of fusion and fission.
Fusion: Unharmful products, hard conditions, large energy input, releases lots of energy.
Fission: Radioactive products, hard to control(chain reaction), no large energy input, releases lots of energy.
What is radioactivity?
The spontaneous decay of an unstable nucleus, releasing either alpha or beta particles + gamma photons if spare energy.
What are alpha and beta particles?
Alpha is helium nucleus (2p, 2n). Beta is high speed electron.
What equation links activity, decay constant and number of radio nuclei>
dN/dt = -λt
What does the decay constant show?
The probability that a nuclei will decay per 1 second.
What equation links no. nuclei, decay constant and time?
N = N0 e^-λt
What equation links half life and decay constant?
t1/2 = ln2/λ
Name two ways to detect radiation?
- Geiger Muller tube
- Photographic plate
What is a use for alpha radiation and why?
Medical tracers and tracing water leaks. Due to short half life and low ionising.
What is a use for gamma radiation?
Fuel rods in nuclear reactors. Long half life and highly ionising (heat water to drive turbines)
Definition of a black body radiator?
One which will absorb all wavelengths of radiation falling on it, at all temperatures.
What equation links luminosity, area and temperature?
L = σAT^4 σ = Stephan-Boltzmann's constant
What range is the visible spectrum of light?
400nm(Violet) - 700nm(Red)
What is Wein’s Law? Look at graphs
λmaxT = 2.90x10^-3
-In kelvin
What are stars?
Stars are massive bodies which emit vast amounts of radiant energy from nuclear reactions within.
What does observed brightness depend on?
- Size
- Surface temp.
- Distance from observer to star
What links intensity, luminosity and distance from observer?
I = L/4πd^2
What is Luminosity and what is intensity?
Luminosity = total power emitted(W) Intensity = radiant flux = power per unit area(Wm-2)
What are two methods of measuring distances to stars?
Parallax, Cepheid variable stars
How does Parallax method work?
Note position of 1st Jan then 1st July. a = r/d as angle is very small.
What is a parsec?
distance of a star with a parallax angle of a 1 second arc. 3.09x10^16m
How does Cepheid variable method work?
- Measure period over which the luminosity varies and you can find the luminosity of Cepheid from graph.
- Then use I = L/4πd^2 to work out distance.
What is a standard candle?
A star of known luminosity
What is odd about the Hertzsprung-Russell diagram axis?
- Temp. axis goes wrong way from 40,000 to 2500
- Logarithmic scales
What equation links wavelength, recessional velocity and speed of light/
Δλ/λ = v/c
What is redshift?
Redshift is due to doppler effect. Galaxies moving away look to have longer λ, so shift to red end of spectrum.
Which galaxies show most redshift?
Farthest galaxies as highest recessional velocity. Must have highest v as all started at one point(big bang)
What links recessional velocity, Hubble constant and distance?
V = H0d, 1/H0 = t
What would lead to open universe?
-Open if av. density < critical value.
What would lead to closed universe?
If av. density > critical value. GPE will be enough to reverse expansion (big crunch)
What would lead to critical universe?
If av. density = critical value.
Why can we not predict the future of the universe?
We can’t detect dark matter, therefore density is unknown. We think with dark matter it is about 1 as gravitational effects on galaxies show.
What is the life cycle of a star similar to our sun size?
Main sequence –> Red Giant –> White Dwarf –> Black Dwarf.
What is the life cycle of a star 3x size of sun?
Main sequence –> Super Giants –> Supernova –> Neutron star
What is life cycle of a star 10x size of sun?
Main sequence –> Super Giant –> Black hole
What are two equations for angular velocity to do with angle?
= θ/t = 2π/T
What is the potential divider equation?
Vin = Vout x (R1/R1+R2)
What does the overall resistance in parallel circuits depend on?
The lowest resistor as that is where the flow would go
