Physics Exam

In the 18th-19th century it was believed heat was a colourless, tasteless odourless fluid called caloric. Each object had a certain amount of caloric and it flowed between objects causing one to heat and the other to cool.

1. All matter consists of tiny particles (atoms, molecules, ions)

2. Electrical forces both attractive and repulsive exist between these particles

3. Particles move constantly in a unpredictable manner

4. Collisions between particles involve no loss of kinetic energy (perfectly elastic)

5. The distances between particles in gas are large compared to the size of the particles

the sum of kinetic and potential energies of all the particles of the particles in the object. Kinetic energy from motion (rotation, vibration movement) and potential energy from electrostatic forces.

The average kinetic energy of an objects particles. Measured in °C.

The transfer of thermal energy between objects because of a difference in temperature. Heat flowers to the body at lower temperature from the body at high temperature until they reach thermal equilibrium. Measured in J.

As an object cools its particles lose kinetic energy. At 0°K (-273.15°C) the particles should theoretically stop completely.

The state of balance when thermal from two contacting bodies is equal.

When a object reaches a specific temperature to change phase, it will remain the same until the whole object is in a different phase. Between solids and liquids, it’s latent head of fusion. Between liquids and gasses, it’s latent heat of vaporisation. (Q=mL, l is Lf or Lv)

Conduction, convection and radiation. Conduction: when two objects at different temperatures are in direct contact, particles between the objects collide and transfer kinetic energy via collisions.

Natural convection: natural motion of fluids or gasses caused by natural forces within. Buoyancy is the main with hotter parts rising whilst denser colder parts sink, forming a convection current transferring heat.

Forced convection: describes the motion of fluid that is caused by forces outside of it. Move faster than natural convection as they’re is a powered source.

Radiation: consists of electromagnetic waves which transmit energy from a source to absorber without any contact, hence no movement of particles. Higher emitter temperature, higher radiation emitted. Objects can absorb and emit simultaneously. Smooth whiter surfaces reflect more radiation whilst darker rougher surfaces absorb more.

Material through which thermal energy flows quickly.

Material through which thermal energy flows slowly.

1. Pump: pushes coolant around the engine

2. Thermostat: releases coolant into the radiator once it reaches a high temperature

3. Radiator: a set of tubes surrounded by thin metal fins which have heat transferred to them to pass to the environment

4. Fan: pulls air through radiator as it increases rate of cooling

1. Compressor: pressurises gas called refrigerant, increasing temperature

2. travels through a set of tubes called a condenser where it releases heat to surroundings and becomes a liquid

3. The refrigerant is depressurised by an expansion valve making it cool down

4. The refrigerant travels through an evaporator absorbing heat from surroundings and turning into a gas

Refrigerative AC’s use heat pumps with the condenser outside where fins and fan assist heat transfer and evaporator inside to absorb heat. The cool air is forced into a room with another fan. Evaporative AC’s force air into a wet filter pad where the heat is absorbed as the water in the pad evaporates and then cool air is forced in with a fan. Doesn’t work on humid days as there is no remaining space between air molecules for more water.

Protons exert electrostatic forces of repulsion on each other over large distances. The strong nuclear force is a great force that’s hold the nucleus together, exerted over short distances between each nucleon regardless of charge.

Some naturally o curing isotopes are unstable, so to become stable they change into another element releasing a particle.

Unstable nuclei that emit particles and/or radiation

When a heavy unstable nucleus undergoes radioactive decay. Positive charge with 2 protons and 2 neutrons, no electrons. 4:2 He or a

Beta-: Unstable atom has relatively large number of neutrons, emitting an electron (beta particle) from nucleus. Neutron splits into a proton, electron and antineutrino. Beta+: Unstable atom has too many protons. Proton decays into a neutron, positron and neutrino. Neutron stays others are emitted. Position is negative electron.

Unstable nuclei dissipate excess energy by emitting photons (electromagnetic energy) of very small wavelength.

Consist of 2 protons and 2 neutrons (+2 charge) Heavy and slow moving, travelling at <10% speed of light. Due to significant mass and charge, can ionise hundreds of thousands of atoms, hence high ionising ability. Each interaction slows it down eventually absorbing 2 electrons from environment turning into helium. Stopped by few cm air or paper / skin. Hence low penetrating ability.

Fast moving electrons (+1 charge ) that travel at <90% speed of light. Small mass and charge means moderate ionising ability. Due to negative charge, repelled by atoms electron colours hence each glancing collision lose less energy from each interaction hence moderate penetrating ability. Can be stopped with few m of air or 1mm aluminium.

Fast moving positrons (antielectrons). When colliding with an electron, annihilation occurs, both particles are transformed into pure energy in 2 gamma rays. Immediately ionising first electron means high ionising ability, but annihilation means very low penetrating ability.

Electromagnetic radiation with very high frequency (energy). No mass and no charge hence travel at speed of light. Low probability of interaction with matter hence very low ironing ability and very high penetrating ability. Can travel through air almost indefinitely, stopped by 40cm lead or 2m concrete.

Alpha and beta get deflected. Alpha towards negative terminal. Beta towards positive terminal. Gamma has no charge hence not affected.

Some forms of radiation are harmful to living things. When ionising radiation interacts with organisms the ions created can damage tissue and lead to cancer.

Measures severity radiation exposure for a certain mass of tissue. D=E/m, E is energy absorbed (J) and m is mass of tissue (kg). Measured in Grays (Gy). 1Gy = 1J/kg.

Type of radiation changes severity of dose. Quality factor determines the relative biological impact of different radiations. QfA= 20 Qf Fast neutrons =10 QfB, G, X-ray =1. DE = D*Qf, D is absorbed dose, Qf is Quality factor. Measured in Seiverts (Sv).

As radioisotopes are unstable, they will randomly emit radiation and decay into a different element. The stability is measured using half-life. It is the time it takes for half the remaining reactive nuclei to decay.

N=No(1/2)^n, N is number, No is original, n is number of half lives

n=T/(t1/2), n is number of half lives, T is time (t1/2) is half life

A= DeltaN/t, Decays per second. DeltaN is number of decays. T is time (s). Measures in Becquerels (Bq) A=Ao(1/2)^n, Ao original activity, n is number of half lives.

When an atomic nucleus splits into two or more smaller nuclei (daughter nuclei and maybe also neutrons). Nuclei capable of fission are said to be fissile. Is a random process.

E=mc^2, E is energy, m is mass and c is speed of light.

Energy that keeps nucleus together. To seperate a nucleus into individual nucleons, this energy must be overcome.

Difference in mass between products and reactants. DeltaM = mass of nucleons - mass of nucleus. = mass of reactants - mass of products

process where neutrons released in fission produce an additional fission reaction in at least 1 further nucleus. This may be controlled (nuclear power) or uncontrolled (weapons).

Fission occurs inside under controlled conditions to produce heat for electricity. Contains fuel rods, moderators, control rods, coolant and shielding.

Most reactors require 3-5% enriched uranium 235 pellets stacked inside long cylinders called fuel rods.

When free neutrons are released by fission, they are too fast to cause fission in other atoms, hence moderators work to slow them down using materials that are unlikely to absorb neutrons such as graphite or water / heavy water. They slow as the free neutrons bounce off the moderator atoms.

Used to slow down chain reactions when they are going too fast. When control rods are lowered into the reaction vessel, they begin to absorb some neutrons released by fuel rods hence slow down reaction or stop entirely. Made of materials that easily absorb neutrons such as boron carbine, silver or cadmium.

Usually water, circulates through the reactor to transfer heat from core to generators. The coolant is generally isolated so that it does not become radioactive. (River cooled).

Reactors are enclosed in a steel case and surrounded by several meters of concrete to prevent radiation from escaping.

Some particles have electrostatic charges (protons +, electrons -). Charge is measures by the letter q in Coulombs (C). A proton has 1.60x10^-19 C (e) and an electron negative that. As charges smaller than e are impossible, all charges must be a multiple of it.

When an object has an uneven number of protons and electrons, it it charged, often happening when two objects run together and the electrons move from one to the other. If the charges do not more it it called static electricity.

All charged particles produce them where other particles experience attractive to repulsive forces. Represented by arrows showing direction a positive charge will experience. Never cross and stronger the furled, closer the lines are.

When charges are separated, there is potential energy difference between them this is voltage. V=E/q, V is voltage, E is electrical energy (J) and q is charge (Coulombs)

Measures the rate of flow of electrons through a system. I=q/t, q is charge t is time and I is current (Amperes (A))

Conventional current flows from positive to negative whilst real flow flows from negative to positive.

Closed loop through which current can flow. Must have a power source and one or mode devices that use energy (load) and pathway electrons can travel.

E=VIt, V is voltage (V), I is current (A) and t is time (s) E is energy (J).

Power is the rate of which energy is transformed by load. P=E/t, P=VI, E is energy (J) t is time (s), V is voltage (V) and I is current (A)

If temperature is consistent, Current is directly proportional to Voltage. Measured in ohms, resistance is the amount components resist current flow. V=IR, I is current (A), R is resistance (Ohms)

When two or more components are connected after eachother on the same conducting pathway. Any break in the circuit stops all components. Voltage in all components ads up to input. Vt=V1+V2…. The current is equal all throughout. It=I1=I2… Total resistance is sum of all resistance. art=R1+R2…

Two or more components are connected on different conducting pathways. A break in one conducting pathways will still allow charge to flow. Voltage in each branch is equal V1=V2… Total current is adds up from each path It=I1+I2… Rt=(R1^-1 +R2^-1…)^-1