specification points Flashcards
what is the first law of thermodynamics
the change of internal energy of the object = the total energy transfer due to work done and heating
what is the temperature of absolute zero in celcius
-273 ℃
what is the work done by an ideal gas equal to
pΔV
what is molar mass equal to
the mass of 1 mol of the substance
what is brownian motion and how can it be observed
the random motion of a particle as a result of collisions with surrounding gaseous molecules.
can be observed in smoke particles under a microsope
boyles law and an equation for it
pressure is inversely proportional to volume
P₁V₁=P₂V₂
charles law and an equation for it
volume occupied by a fixed amount of gas is directly proportional to its absolute temperature, if the pressure remains constant.
V₁/T₁=V₂/T₂
pressure law (gay-lussac) an equation for it
pressure of a given mass of gas is directly proportional to the absolute temperature of the gas, when the volume is kept constant.
P₁/T₁=P₂/T₂
what are the 5 assumptions of the kinetic theory model
1: molecules move in random motion
2: they do not attract eachother
3: volume of each molecule is negligible compared with the volume of the gas
4: the collisions with eachother and the container are elestic collisions
5: each collision with the container surface is of much shorter duration than the time between impacts
what are the simalarities between electrostatic and gravitational forces
both have inverse square laws of force
field lines, use of potential concept, equipotential surfaces etc
what are the differences between electrostatic and gravitational forces
masses always attract, but charges may attract or repel
gravitational potential definition
the gravitational potential, V, at a point is the work done per unit mass to move a small object from infinity to that point
what is an equipotential
a line or surface in a field along which the electric or gravitational potential is constant
graphical representation of g against r
graphical representation of v against r
what is the area under a graph of g against r
ΔV
derive keplers third law T² ∝ r³
start with GM/r² = V²/r
uses speed = distance/time
arrives at r³/T² = GM/4𝜋²
what is the equation for escape velocity
Vesc = √2GM/R = √2gR
what is the equation for the energy of a satelite in circular orbit of radius r
(and derive it lmao get fukt)
E = -(GMm/2r)
what is geostationary orbit
orbits at a fixed position relative to the planet and at the same time period of the planet
what is the definistion of Tesla
The magnetic flux density is 1 T when a wire carrying a current of 1 A placed at right angles to the magnetic field experiences a force of 1 N per metre of its length.
magnetic flux density definition
force per unit length per unit current on a current carrying conductor at right angles to the magnetic field lines
what is faradays law
the induced emf in a circuit is equal to the rate of change of flux linkage through the circuit
what is lenzs law
the direction of the induced emf is always such as to oppose the change that causes it
describe how a cyclotron works
A source of charged particles is placed at the centre of the cyclotron and they are fired into one of the electrodes
The magnetic field in the electrode makes them follow a semi-circular path, since it is perpendicular to their motion until they eventually leave the electrode
The potential difference applied between the electrode accelerates the particles across the gap to the next electrode (since there is an electric field in the gap)
Since the speed of the particles is now higher, they will follow a circular path with a larger radius (since r ∝ v) before leaving the electrode again
The potential difference is then reversed so the particles accelerate towards the opposite electrode
This process is repeated as the particles spiral outwards and eventually have a speed large enough to exit the cyclotron
what is the root mean square value of an alternating current and the equation
the value of the direct current that would give the same heating effect as the alternating current in the same resistor
Irms = I₀ / √2
what are eddy currents
Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of induction.
what is the peak to peak value of an ac and pd
the maximum voltage change occurring during one cycle of alternating voltage or current.
The peak-to-peak value of an AC voltage is defined as the difference between its positive peak and its negative peak.
( 2 x the peak value )
what are 3 characteristics of transformers that increase efficiency
1: low resistance windings, to reduce power wasted due to heating effect of the current
2: a laminated core (layers of iron seperated by layers of insulator). eddy currents induced in the core are reduced in this way, so their heating effect is reduced
3: soft iron core, which is easily magnetised and demagnetised. Reduces power wasted through repeated magnetisation and demagnetisation of the core
list an apllication for each alpha, beta and gamma radiation
alpha: smoke detector
beta: paper mill (thickness monitering)
gamma: radiotherapy
what is the inverse square law for gamma radiation
the intensity varies with the inverse square of distance
I ∝ 1/r²
what were the conclusions rutherford came to from the scattering experiment?
- most of the atoms mass is concentrated in a small region, the nucleus, at the centre of the atom
- nucleus is positively charged
- magnitude of charge is +Ze where e is the charge of the electron and Z is the atomic number
explain rutherfords alpha scattering experiment
a thin metal foil was placed in the path of a narrow beam of 𝜶 particles
this caused the alpha particles to scatter
a flourescent screen is set up so it could be moved in a circular path around the foil
most alpha particles passed straight through the foil with little or no deflection - about 1 in 2000 were deflected
about 1 in 10000 particles were deflected through angles more than 90°
how should radioactive materials be stored
lead lined containers thick enough to reduce gamma radiation from the sources to around background level
how should radioactive sources be handled
- no source should come into contact with skin
- handled via robots or long handle tongs etc
why does background radiation exist
radiation due to naturally occuring radioactive substances in the enviroment
how should radioactive waste be stored
buried underground encased in glass (vitrified) and in a steel barrel
what is radioactive dating
using radioactive isotopes in an ancient object to determine the age of the object by comparing:
- the activity per unit mass of the isotope with the activity per second of the same isotope in a recently formed object
- the ratio of number of atoms of the radioactive isotope to the number of atoms of the isotope it decays into, provided the second isotope is stable
metastable state
a long lived excited state after alpha or beta emission that lasts long enough for the radioactive isotope to be seperated from the parent isotope
explain the graph of N against Z for isotopes
for light isotopes, stable nuclei follow the straight line N=Z
for heavier isotopes (increase in Z ) the nuclei have more neutrons than protons. This is to help balance out the forces in the nucleus (electrostatic and string nuclear)
what is electron capture
proton-rich nucleus absorbs an inner atomic electron. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino
how would you estimate the radius of the nucleus from closest approach of an alpha particle
Ke = Pe
Ke = Qq / 4𝜋ε₀d
re arrange for distance
nuclear diameter is in the order of 10^-15m
what is the value of R₀ in the nuclear radius equation
1.05fm = 1.05 x 10^-15 m
what is the mass defect of a nucleus
difference between the mass of the seperated nucleons and the mass of the nucleus
what is the binding energy of a nucleus and its equation
the work that must be done to seperate a nucleus into its constituent neutrons and protons
E = Δmc²
where Δm is the mass defect
can also be calculated easily by converting mass defect in u, to MeV by multiplying by 931.5
sketch the graph of average binding energy per nucleon against nucleon number
what is nuclear fission
the process in which a large unstable nucleus splits into two fragments which are more stable than the original nucleus. each fission event releases energy and 2 or 3 neutrons (referred to as fission neutrons)
binding energy per nucleon increases in this process
what is nuclear fusion
two nuclei combine to from a bigger nucleus. The binding energy per nucleon of the product nucleus is greater than of the inital nuclei. energy is released equal to the increase of binding energy
what do control rods do in a thermal nuclear reactor
absorbs neutrons, which in turn control the rate of fission events
often made from materials such as boron
what does the moderator do in a thermal nuclear reactor
slows down the fission neutrons so they can cause further fission events
moderator is often water or graphite
what does the coolant do in a thermal nuclear reactor
pumped through steel pipes between the reactor core and the moderator so that it transfers energy from the reactor vessel to the heat exchanger
often water or carbon dioxide gas
what are some safety aspects of a thermal nuclear reactor
- reactor core is a thick steel vessel absorbs beta radiation and some gamme radiation and neutrons from the core
- core is surrounded by very thick concrete walls which absorb the neutrons and gamma radiation that escape the vessel
- emergency shut down system that inserts control rods fully and stops fission completely
- fuel rods are inserted and removed remotely
