Topic 1 Physics 2 Revision NotesStatic and current electricity1.1 An atom has 3 particles – protons and neutrons in the nucleus, electrons around the outside.

1.2 An insulator can be charged by friction, through the transfer of electrons

1.3 The material gaining electrons becomes negativelycharged and the material losing electrons is left with an equalpositive charge

1.4 Like charges repel and unlike charges attract

1.5 Common electrostatic phenomena occur because of the movement of electrons,

These include:a) shocks from everyday objectsb) lightningc) attraction by induction such as a charged balloon attracted toa wall and a charged comb picking up small pieces of paper.Electrons on balloonrepel electrons in wall andare attracted to positive charges in wall

1.6 Earthing removes excess charge by movement ofelectrons

1.7 Explain some of the uses of electrostatic charges in everydaysituations, including paint and insecticide sprayers

1.8 Dangers of electrostatic charges in everyday situations include fuellingEarth wire conducts charge away

aircraft and tankers together with the use of earthing to preventthe build-up of charge and danger arising

1.9 Electric current is the rate of flow of charge

1.10 Current in metals is a flow of electrons

1.11 Use the equation:

charge (coulomb, C) = current (ampere, A) × time (second, s)Q = I × t

1.12 Cells and batteries supply direct current (d.c.)

1.13 Direct current (d.c.) is movement of charge in one direction onlyUnit P2: Physics for your future

Topic 2Controlling and using electric current

2.1 Ammeter - placed in series with a component to measure the current, in amps, in the component

2.2 Explain how current is conserved at a junction

2.3 The current in a circuit depends on the potential difference of the source

2.4 A voltmeter is placed in parallel with a component to measure the potential difference (voltage), in volts (V), across it

2.5 Potential difference (voltage) is the energy transferred per unit charge passed.

In other words: a volt is a joule per coulomb. Volt = Joule / Coulomb (J = V x C)

0

2.6 Investigate the relationship between potential difference(voltage), current and resistance

2.7 The bigger the resistance , the smaller the current in a circuit. A variable resistor can change the resistance (like a dimmer switch).

2.8 Use the equation:potential difference (volt, V) = current (ampere, A) × resistance (ohm, Ω)V = I × R

Bigger resistance = smaller current

Smaller resistance = bigger currentVariable resistor

LEARN THIS! NOT ON EXAM EQUATION LIST!

2.9 Current varies with potential differencefor the following devices

a filament lamps

b diodes

c fixed resistors

2.10 Light dependent resistor (LDR): the brighter the light the lower the resistance (and the bigger the current).

2.11 Thermistor:the hotter/higher the temperature, the lower the resistance (and the bigger the current).

2.12 When there is an electric current in a resistor, there is an energy transfer which heats the resistor

2.13 The energy transfer (in 2.12 above) is a resultof collisions between electrons and the ions in the lattice

2.14 Advantages and disadvantages of the heating effect of an electric current:Advantages: heaters, kettles, hairdryers, washing machines, tumble dryers etc (NOT microwaves!)Disadvantages: computers, TVs, projectors – they need fans to remove heat

2.15 Use the equation:

electrical power (watt, W) = current (ampere, A) × potential difference (volt, V)

P = I × V

2.16 Use the equation:

1 = Ions in the lattice

2 = Free electrons

2

1

energy transferred (joule, J) = current (ampere, A) × potential difference (volt, V) × time (second, s)

E = I × V × tUnit P2: Physics for your future

Topic 3Motion and forces

3.1 Vector quantities have 2 things: SIZE and DIRECTION. These are vector quantities:

Vector quantities (size and direction)

NOT vectors (just size, no direction)

displacement distancevelocity speed

acceleration massforce temperature

momentum

3.2 Distance – time graphs: Straight sloping line = constant speed Horizontal (flat) line = stopped The steeper the line, the faster the speed.

3.3 Velocity is speed in a stated direction. e.g. 20 m/s = speed 20 m/s North = velocity

3.4 speed (m/s) = distance (m) / time (s)

3.5 acceleration = change in velocity / time taken (m/s2) (m/s) (s)

3.6 Velocity – time graphsa the steeper the line, the greater the accelerationb the acceleration can be calculated from the graphc distance travelled = area under the graph (higher)

3.7 Free-body force diagrams – ALWAYS draw a box.

Put 1, 2, 3 or 4 arrows on it:

3.8 When two bodies interact, the forces they exert on each other are equal in size and opposite in direction and that these are known as action and reaction forces

3.9 Calculate a resultant force:

3.10 If the resultant force acting on a body is zero, it will remain at rest or continue to move at the same velocity

3.11 If the resultant force acting on a body is not zero, it will accelerate in the direction of theresultant force – see truck diagram above for 3.9

3.12 The acceleration of an object depends on 2 things:

a) The size of the resultant forceb) The mass of the object

or… The smaller the mass and the bigger the force, the GREATER the acceleration.

Eg a sports car with a big engine accelerates faster than a bus with a small engine.

3.13 Use the equation:

Resultant force = 100N – 60N = 40N in this direction

Truck accelerates

Friction force 60N Engine force 100N

Engine force

100N

Friction force

60N

Resultant force = 40N

Resultant force = 0N: Object stays still

OR

Resultant horizontal force = 0N: plane moves at constant speed

Resultant vertical force = 0N: plane flies at constant height

force (newton, N) = mass (kilogram, kg) × acceleration (metre per second squared, m/s2) F = m × a

3.14 weight mass gravitational field strength (newton, N) = (kilogram, kg) × (newton per kilogram, N/kg)

W = m × g

3.15 Investigate the relationship between force, mass and acceleration

3.16 Recall that in a vacuum all falling bodies accelerate at the same rate

3.17 a) when an object falls through an atmosphere, air resistance increases with increasing speed b) air resistance increases until it is equal in size to the weight of the falling object c) when the two forces are balanced, acceleration is zero and terminal velocity is reached

Topic 4Momentum, energy, work and power

4.1 The stopping distance of a vehicle =

thinking distance + braking distance

4.2 Factors affecting the stopping distance of a vehicle, including:a the mass of the vehicleb the speed of the vehiclec the driver’s reaction timed the state of the vehicle’s brakese the state of the roadf the amount of friction between the tyre and the road surface

4.3 Investigate the forces required to slide blocks along differentsurfaces, with differing amounts of friction

4.4 Use the equation:

momentum = mass × velocity (kilogram metre per second) (kilogram) (metres per second) (kg m/s) (kg) (m/s)

to calculate the momentum of a moving object

4.5 Momentum is a vector quantity because it has SIZE and DIRECTION (+ OR - direction)

4.6 Linear momentum is conserved:

(1000kgm/s – 1000kgm/s = 0)

4.7 The faster the rate of change of momentum, the bigger the force. (The faster you speed up or stop, the bigger the force you feel.)

Bubble wraps, seat belts, crumple zones and air bags INCREASE the time to stop. This means less force.

It is the big force thatcauses bad injuries

Cars have crumple zones

Before:

Total momentum = 0 kgm/s (Nothing moving!)

After

Total momentum = 0 kgm/s

Canon:

1000kg x -1m/s

= -1000kgm/s

Ball:

10 kg x100m/s

= 1000kgm/s

Canon + ball:

1010kg x 0m/s

= 0kgm/s

Unit P2: Physics for your future

4.8 Investigate how crumple zones can be used to reduce the forcesin collisions

4.9 Higher:

force = change in momentum ÷ time (Newton) (kilogram metre per second) (second) N) (kg m/s) (s)

F = (mv – mu) ÷

t

4.10 work done = force x distance moved (joule) = (newton) (metre)

(J) = (N) × (m)

E = F × d

4.11 Energy transferred (joule, J) = work done (joule, J)

Eg If a car brakes, and the brakes do 10,000J of WORK, then 10,000J of kinetic ENERGY are transferred into 10,000J of thermal (heat) ENERGY. Energy and work are kind of the SAME THING.

4.12 Power is the rate of doing work and is measured in watts, W (same as 4.14)

4.13 Use the equation:

power (watt, W) = work done (joule, J) / time taken (second, s)

4.14 One watt is equal to one joule per second, J/s

4.15 Use the equation:

gravitational potential energy = mass x gravitational field strength x height (joule) = (kilogram) x (newton per kilogram) x (metre) (J) = (kg) x (N/kg) x (m)

GPE = m × g × h

4.16 Use the equation:

kinetic energy = ½ × (mass) × velocity2

(joule) = ½ x (kilogram) × (metre/second)2

(J) = ½ x (kg) x (m/s)2

KE = ½ × m × v2

4.17 Energy is always conserved. That means all the energy that you start with is converted into other forms

eg 1 If a car has 10,000J of Kinetic Energy and brakes to a stop, all the 10,000J of KE is changed into 10,000J of heat and sound energy by the brakes.

Eg 2 If a person of mass 100kg jumps up 0.2m, the GPE = m x g x h = 100 x 10 x 0.2 = 200J

The kinetic energy of the person when they start to jump must be = 200J.

The kinetic energy is all changed into gravitational potential energy (ie it is conserved).

4.18 Carry out calculations on work done to show the dependence of braking distance for a vehicle on initial velocity squared (work done to bring a vehicle to restequals its initial kinetic energy)

ExampleThese examples show 4 braking tests for the same car. The braking force is the same each time: same car = same brakes.

U = the initial velocity of the car

The kinetic energy depends on v2

i.e. if your speed increases by x2 (double) the KE increase by 22 = x4

AND the braking distance increases by x4

(3 x speed = 32 = 9 x braking distance)

Topic 5Nuclear fission and nuclear fusion5.1 atomic (proton) number = bottom number = number of protons mass (nucleon) number = top number = number of protons + neutrons

12 C 6

13 C 6

14 C 6

5.2 Ions are charged particles. Atoms may gain electrons to form –ve ions. Atoms may lose electrons to make +ve atoms. Atoms can gain an electron from another atom, or lose an electron to another atom.

Ionising radiation knocks electrons off atoms to make ions.

5.3 Alpha and beta particles and gamma rays are ionizing radiations emitted from unstable nuclei in a random process

5.4 An alpha particle is a helium nucleus, a beta particle is an electron emitted from the nucleus and a gamma ray is electromagnetic radiation

5.5 Compare alpha, beta and gamma radiations in terms of their abilities to penetrate and ionize (ionize = knock electrons off atoms)

5.6 Nuclear reactions can be a source of energy, Fission = splitting the nucleus of an atom to release heat (eg nuclear power station)Fusion = joining nuclei together to release heat energy (eg Sun)Radioactive decay = releases heat (eg to power a satellite or Mars rover)

5.7 The fission of U-235 produces two daughter nuclei and two or more neutrons, accompanied by a release of energy:

5.8 In a controlled nuclear chain reaction: Slow moving neutrons absorbed by more

U-235 nuclei which split, releasing energyand MORE neutrons etc etc

5.9 The chain reaction is controlledin a nuclear reactor usingmoderators and control rods

moderators: slow down fast moving neutrons sothey can be absorbed by nucleuscontrol rods: absorb neutrons = reduces reaction

5.10 In a nuclear power station, thermal (heat) energy from the chain reaction is used to heat water. Thewater turns to steam, the steam turns a turbine.The turbine turns a generator. Generator generateselectricity.

5.11 The products of nuclear fission are radioactive

5.12 Nuclear fusion is the creation of larger nuclei fromsmaller nuclei, accompanied by a release of energy. Fusion is the energy source for stars.

5.13 Explain the difference between nuclear fusion and nuclear fission

5.14 Nuclear fusion does not happen at lowtemperatures and pressures, due to electrostaticrepulsion of protons. The temperatures need to behigh so the nuclei are going fast enough to overcomethe repulsive electrostatic force.

5.15 It is very difficult and expensive to maintain the high temperaturesneeded for fusion. It is therefore very difficult to make a fusion power station – it could be many years until it happens.

5.16 New scientific theories, such as ‘cold fusion’, are not accepted until they have been validatedby the scientific community – ie a team of scientists claimed to have made a cold fusion reactor. Only when other scientists tried to repeat the experiment did they find it did not work. Only when experiments can be repeated by different scientists are they accepted as scientific theory.

Topic 6

Advantages and disadvantages of using radioactive materials

6.1 Background radiation is low level radiation. Regional variations within the UK are caused in particular by radon gas which is given out by radioactive decay of uranium in rocks.

6.2 Background radiation comes from natural and human made sources e.g. cosmic rays from space, rocks (radon gas), food, buildings,medical uses, nuclear power stations).

6.3 Use of radioactivity, include:

a household fire (smoke) alarms b irradiating food

c sterilisation of equipment d tracing and gauging thicknesses

e diagnosis and treatment of cancer

6.4 The activity of a radioactive source decreases over timenit P2: Physics for your future6.5 The unit of activity of a radioactive isotope is the Becquerel, Bq

6.6 The half-life of a radioactive isotope is the time takenfor half the undecayed nuclei to decay

6.7 Use the concept of half-life to carry out simple calculations on the decay of a radioactive isotope, including graphical representations

6.8 Investigate models which simulate radioactive decay

6.9 Dangers of ionizing radiation: tissue damageand possible mutations. A mutation is a change inDNA which can lead to cancer.

People working with radiation wearprotective clothing and hold radioactive sourceswith tongs.

6.10 Describe how scientists have changed their ideas of radioactivity over time, including:a the awareness of the hazards associated with radioactive sources: people put radioactive thorium and radium in food and face cream because they thought it was good for them – whoops!

b why the scientific ideas change over time – eg Marie Curie and other people working with radiation got cancer.

6.11 Discuss the long-term possibilities for storage and disposal of nuclear waste

Nuclear waste comes in 3 types:

Possible disposal methods:

Method of disposal ProblemsFiring into space Launch vehicle could explode / fall back to Earth,

spreading radiation over wide areaDumping at sea in barrels Barrels can corrode and release radiation materials

Type of waste How long radioactive? How stored?HLW: High level waste very radioactive for 50 years Thick concrete containers and sealed in

glass. Stored in canisters until it becomes ILW

ILW: Intermediate level waste slightly radioactive for tens of thousands of years

Thick concrete containers. None has been disposed of yet!

LLW: Low level waste moderately radioactive for tens of thousands of years

Compacted and buried in special landfill sites (radiation might leak into soil or water)

into sea which would get into food chainsStorage underground Site needs to be geologically stable ie low risk of

earthquakes

6.12 Evaluate the advantages and disadvantages of nuclear power for generating electricity, including the lack of carbon dioxide emissions, risks, public perception, waste disposal and safety issues

Disadvantages

1. Poisonous waste is produced, some of which is highlyradioactive.

2.  Disposal of this radioactive waste has not beensafely achieved. Very long half-lives (thousands of years)mean that the waste will be a danger "forever".At present the most dangerous waste is sealed in glass-like blocks which are buried deep within "stable" rocks. Careless disposal of waste in the past has led to pollution of land, rivers and the ocean.

3. The power station is potentially dangerous to large areas of the planet. Despite reassurances from the nuclear industry that nuclear power is safe, serious accident have happened and large areas have been contaminated with radioactivity.

4. Many members of the public have become cynicalabout promises of the cleanliness and safety of nuclear power.

5. The power station is very expensive to buildand to safely dismantle afterwards (called decommissioning).When the costs are taken into account, theelectricity produced by the power station is relatively expensive.

Advantages

1. A large amount of energy is generated from a very small amount of fuel.

2. The fuel is readily available. If you need more energy, you just use more fuel.

3.  Nuclear Power does not producecarbon dioxide or sulfur dioxide and so doesnot contribute to global   warming  or acid   rain .