Physics Unit 5 Definitions

Front 1

Boyle's law

Back 1

At a constant temperature, the pressure and volume are inversely proportional

Front 2

Charles' law

Back 2

At constant pressure, the volume of a gas is directly proportional to its absolute temperature

Front 3

The pressure law

Back 3

At constant volume, pressure of an ideal gas is directly proportional of its absolute temperature

Front 4

Avogadro constant

Back 4

Number of atoms in exactly 12g of the carbon isotope C12, equal to 6.02x10^23

Front 5

Internal energy of a gas

Back 5

The sum of the randomly distributed kinetic and potential energies of all its particles

Front 6

Specific heat capacity

Back 6

Amount of energy needed to raise the temperature of 1kg by 1K (Q=mct)

Front 7

Specific latent heat

Back 7

The quantity of thermal energy needed to be gained or lost to change the state of 1kg of a substance (vaporisation or fusion) (Q=ml)

Front 8

Ideal gas

Back 8

Ideal gas follows 3 gas laws, describing how fixed mass behaves when you change temperature, pressure or volume (work on Kelvin scale = °C + 273)

Front 9

Ideal gas assumptions in kinetic theory

Back 9

All molecules identical, molecules have negligible volume compared to volume of container, movement random, newtons laws of motion obeyed, elastic collisions between molecules and container, molecules move in straight lines and force acting during collisions act for less time than time between collisions. Ideal gas when obeyed with temperature low compared to boiling point and pressure not too high.

Front 10

Rutherfords alpha experiment

Back 10

Stream of alpha particles from radioactive source fired at thin gold foil, strike fluorescent screen around foil to detect alpha 360°

Front 11

Rutherfords conclusions

Back 11

Atom must be mainly empty space because most alpha particles pass through, nucleus must have large positive charge because some atoms deflected by large angle, nucleus must be tiny because few particles repelled more than 90° and most of mass must be in the nucleus since fast alpha particles deflected.

Front 12

Electron diffraction

Back 12

Leptons don't interact with the strong nuclear force, so accurate method to measure nuclear radius. Electrons show wave particle duality so can be diffracted, the De broglie wavelength for a moving beam at high speeds is very low so very accurate diffraction pattern on the screen

Front 13

Radiation types

Back 13

Alpha - absorbed by paper, skin or 4cm of air

Beta - absorbed by 3mm aluminium

Gamma - absorbed by few cm of lead, or several metres of concrete

Front 14

Applications of alpha radiation

Back 14

Highly ionising (10000 per mm in air) but don't travel very far. Used for smoke alarms because current flows but short distance so when smoke get in way, alarm goes off.

Front 15

Applications of beta radiation

Back 15

Lower mass and charge than alpha so ionised less (100 per mm in air) but travel further. Used to control the thickness of materials, by the amount of radiation absorbed by detectors - determining the thickness of the material

Front 16

Applications of gamma radiation

Back 16

Very weakly ionising and doesn't do much damage to the body. Used in medicine, as a radioactive tracer - gamma rays with short half lives used in a PET scanner.

Front 17

Inverse square law

Back 17

Inverse of radiation is the amount of radiation per unit area, decreases further away from source

Front 18

Safe handling of radioactive sources

Back 18

Always keep source away from body when transporting, long handling tongs should be used, gamma should be stored in a lead box, have radioactive sources outside boxes as little as possible

Front 19

Rate of radioactive decay

Back 19

Completely random, each nucleus has a constant decay probability, decay constant is the probability of a specific nucleus decaying per unit time, activity is the number of nuclei that decay from a sample per second, number of unstable nuclei decreases exponentially with time

Front 20

Hard to get reliable age from radioactive dating because:

Back 20

For man made objects only find age of material not object, may be contaminated by other radioactive sources, may be high background count obscuring objects count, uncertainty in amount of carbon 14 that existed many years ago and sample size may be small so statistically unreliable

Front 21

Medical diagnosis

Back 21

Technetium 99m, injected into patient then moves to region of interest, emission is recorded and image inside patient is produced. Suitable because emits gamma radiation, has a half life of 6 hours and decays to more stable isotope

Front 22

Storage of radioactive waste

Back 22

Need to be stored for hundreds of years until activity of radioactive isotopes has fallen to safe levels. Very long half life so stays highly radioactive for very long time.

Front 23

Nuclear stability

Back 23

Nucleus held by balance between the strong nuclear force and electromagnetic force. A nucleus will be unstable if: too many or too few neutrons, too heavy or too much energy. Alpha released if atoms of massive, beta minus emitted if neutron rich (beta plus proton rich) and gamma emitted when excess energy and produced when electrons are captured

Front 24

Mass defect

Back 24

Mass of nucleus less than mass of its constituents. Mass defect is the difference between mass number and mass of an isotope = binding energy.

Front 25

Average binding energy per nucleon

Back 25

Total binding energy divided by nucleon number. Higher average binding energy means more stable atom (Fe56 most stable). Only elements left of Fe56 can fuse and only elements right of Fe56 can fission

Front 26

Nuclear fission

Back 26

Large nuclei are unstable and some randomly split into 2 smaller nuclei, process spontaneous if happens by itself, or induced if encouraged. Energy released because new nuclei have higher average binding energy per nucleon. Larger nuclei more likely to spontaneously fission because less stable so limited number of elements produced.

Front 27

Nuclear fusion

Back 27

2 light nuclei can combine to create a larger nucleus, a lot of energy is released because new heavier nuclei have much higher average binding energy per nucleon. Nuclei all positively charged so electrostatic force of repulsion between them. Nuclei only fuse if overcome the electrostatic force and get close enough for strong interaction to bind them together (about 1MeV of Ek needed)

Front 28

Chain reactions

Back 28

Fission reactions produce more neutrons inducing other fission reactions, a critical mass is the amount of fuel needed to continue a chain reaction. A sub critical mass results in reaction petering out, super critical mass used where several new fission follow each fission controlled using control rods.

Front 29

Moderator

Back 29

Moderator used to absorb neutrons and to slow them down so that they can cause further fission, keeping the reaction at a steady rate. Neutrons slowed through elastic collisions with the moderator (usually use water but other liquids can be used). Final velocity of neutron needs to be close to 2200ms-1, mass of moderator particle needs to be similar to neutron.

Front 30

Control rods

Back 30

Control rods limit the number of neutrons in the reactor, made up of usually boron to absorb the neutrons - inserted by varying amounts to control the reaction rate.

Front 31

Coolant

Back 31

Sent around the reactor to remove heat produced by fission, often same liquid used in moderator, heat then generates steam for powering electricity generating turbines.

Front 32

Reactor safety

Back 32

Shielding - reactor is surrounded by thick concrete case, preventing radiation escaping and reaching people working there.

Emergency shut down - shut down immediately by releasing control rods into the reactor, they were lowered fully into reactant to slow down as quickly as possible.

Handling and storing fission waste products - unused uranium fuel rods emit alpha so easily contained. Spent fuel rods are more dangerous since they have larger proportion of neutrons than nuclei of a similar atomic number, making them unstable and radioactive, they emit beta and gamma which is highly penetrative. Initially very hot so remotely placed in cooling ponds until temperature reaches safe level, shouldn't be stored in sealed containers until activity has fallen sufficiently.

Front 33

Nuclear power pros vs cons

Back 33

Benefits - very efficient, lost of nuclear fuel currently, doesn't release greenhouse gases

Disadvantages - waste products, nuclear disasters

Front 34

Cathode rays

Back 34

Causes glow on wall of a discharge tube, rays seemed to come from the cathode. Cathode rays have: energy momentum and mass, negative charge, same properties irrespective of gas in tube, much bigger specific charge than hydrogen (thought to have very small mass). Concluded cathode rays were just beams of electrons.

Front 35

Thermionic emission

Back 35

Heat a metal cathode and free electrons gain Ek, sufficient energy and they will break free from the surface of the metal, once emitted accelerated by a high voltage causing an electric field towards the anode in an electron gun. Air evacuated so electrons can travel freely and no collisions. Beyond cylindrical anode, no electric field so move at constant velocity.

Front 36

Electronvolt

Back 36

1 eV is the Ek carried by an electron after it has been accelerated from rest through a pd of 1 volt. Energy gained in eV = accelerating voltage in V

Front 37

Specific charge

Back 37

Charge per unit mass measured in Ckg-1. Largest thought to be hydrogen atoms but electrons found to be 1800 times greater

Front 38

Fine beam tube to find specific charge of electron

Back 38

Beam of electrons from electron gun passed through hydrogen gas, colliding with hydrogen atoms along its path and transfer some energy causing electrons to be excited. As return to ground state, either light so electrons seen as glowing trace. 2 mag field coils either side of tube generate mag field perpendicular to electron beam so beam follows circumstances ulnar motion.

Front 39

Stokes' law

Back 39

When an object is dropped into a fluid and feels a viscous drag force acting in opposite direction to objects velocity and is due to its viscosity.

Front 40

Millikan's oil drop

Back 40

Atomiser created a mist of oil drops charged by friction (positive if lost electrons and vice versa). Some drops fell into top plate and could be viewed by microscope. Forces acting before pd: mg acting downwards, stokes law acting upwards, at terminal velocity 2 equal each other and rearrange for radius. Forces acting with pd: mg downwards and uniform electric field acting upwards, when stationary 2 are equal.

Front 41

Quantisation of electric charge

Back 41

Charge exists in packets of size 1.60×10-19 C which is the fundamental unit of charge - amount carried by an electron

Front 42

Newtons corpuscular theory

Back 42

Light made up of streams of particles called corpuscles. Light was known to travel in straight lines, reflect and refract, theory based on his laws of motion. Reflection due to force pushing particles away from surface. Refraction due to corpuscles travelling faster in a denser medium.

Front 43

Huygen's wave theory

Back 43

Every point on a wavefront may be considered to be a point source of secondary wavelets that spread out in the forward direction at the speed of the wave. The new wavefront is the surface that is tangential to all of these secondary wavelets. Predicted light would slow down when in a denser medium, reflection explained by angle of incidence = angle of reflection, should diffraction and interfere.

Front 44

Why Huygens rejected?

Back 44

Diffraction was undetectable by equipment available at the time, no supporting evidence, Newton was the man and had evolutionised physics so his theory accepted, Huygens explained waves as longitudinal but light could be polarised which is only a property of transverse waves, couldn't explain why shadows caused by light.

Front 45

Young double slit experiment

Back 45

Diffracted a coherent light source to create 2 coherent light sources and they diffracted through double slit. At whole pathlengths, constructively interfered and bright fringes seen. At half pathlengths, destructively interfered and deal fringes seen. Interference and diffraction uniquely wave properties.

Front 46

Light as an electromagnetic wave

Back 46

Electromagnetic waves are transverse waves made up of oscillating electric and magnetic fields that are perpendicular to each other and also to the direction of travel. Predicted a spectrum of EM waves travelling at the same speed with different frequencies.

Front 47

Fizeau's speed of light

Back 47

Knew time and distance so used frequency of rotation and number of gaps to estimate speed of light - close to maxwells speed

Front 48

Radio waves

Back 48

Radio waves produced when high voltage sparks jump across a gap of air (used induction coil and capacitor to produce a high voltage). Detected the waves using a loop of wire with a gap in with sparks induced by radio waves, showing waves had magnetic component. Also have electric component because radio waves create alternating current.

Front 49

Stationary radio waves

Back 49

Stationary wave is the superposition of 2 progressive waves with the same frequency and amplitude moving in opposite directions. Created by reflecting progressive wave back on itself. If whole number of waves produced, called resonant frequencies where vibrates up and down. 0 amplitude = node, max amplitude = anti node.

Used detector to find distance between 2 nodes = half a wavelength and used c=f × wavelength.