Topic 1Physics 2 Revision Notes
Static and current electricity
1.1 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 negatively
charged and the material losing electrons is left with an equal
positive charge
1.4 Like charges repel and unlike charges attract
1.5 Common electrostaticphenomena occur
because of the movement of electrons,
These include:
a) shocks from everyday objects
b) lightning
c) attraction by induction such as a
charged balloon attracted to
a wall and a charged comb
picking up
small pieces of paper.
Electrons on balloon
repel electrons in wall and
are attracted to positive
charges in wall
1.6 Earthing removes excess charge by movement of
electrons
1.7 Explain some of the uses of electrostatic charges in everyday
situations, including paint and insecticide sprayers
1.8 Dangers ofelectrostatic charges in everyday situations include fuelling
aircraft and tankers together with the use of earthing to prevent
the 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.) ismovement of charge in one direction only
Unit P2: Physics for your future
Topic 2
Controlling and using electric current
2.1 Ammeter - placed in series with a
componentto 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
potentialdifference of the source
2.4 A voltmeter is placed in parallel with a componentto 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:
avolt 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
2.9 Current varies withpotential difference
for the following devices
a filament lamps
b diodes
c fixed resistors
2.10 Lightdependentresistor (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, thereis an energy transfer which heats the resistor
2.13 The energy transfer (in 2.12 above) is a result
of collisions between electrons and the ions in the lattice
2.14 Advantages and disadvantages of theheating 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) × potentialdifference (volt, V)
P = I × V
2.16 Use the equation:
energy transferred (joule, J) = current (ampere, A) × potentialdifference (volt, V) × time (second, s)
E = I × V × t
Unit P2: Physics for your future
Topic 3
Motion and forces
3.1 Vectorquantities have 2 things: SIZE and DIRECTION. These are vector quantities:
Vector quantities (size and direction) / NOT vectors (just size, no direction)displacement / distance
velocity / speed
acceleration / mass
force / 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 graphs
a the steeper the line, the greater the acceleration
b the acceleration can be calculated from the graph
c 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 andopposite in direction and that these are known as
action andreaction forces
3.9 Calculate a resultant force:
3.10 If the resultant force actingon a body is zero, it will remain at rest or continue to move atthe same
velocity
3.11 If the resultant force actingon a body is not zero, it will accelerate in the direction of the
resultant 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 force
b)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:
force (newton, N) = mass (kilogram, kg) × acceleration (metreper second squared, m/s2)
F = m × a
3.14 weight mass gravitationalfield strength
(newton, N) = (kilogram, kg) × (newton per kilogram, N/kg)
W = m × g
3.15 Investigate the relationship between force, mass andacceleration
3.16 Recall that in a vacuum all falling bodies
accelerate at the samerate
3.17 a) when an object falls through an
atmosphere, air resistanceincreases
with increasing speed
b) air resistance increases until it is
equal in size to the weightof the
falling object
c) when the two forces are balanced,
acceleration is zero and
terminal velocity is reached
Topic 4
Momentum, energy, work and power
4.1 The stopping distance of a vehicle =
thinking distance + braking distance
4.2 Factors affecting thestopping distance of a vehicle, including:
a the mass of the vehicle
b the speed of the vehicle
c the driver’s reaction time
d the state of the vehicle’s brakes
e the state of the road
f the amount of friction between the tyre and the road surface
4.3 Investigate the forces required to slide blocks along different
surfaces, 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 momentumis 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.)
Bubblewraps, seat belts, crumple zones and air bags INCREASE the time to stop. This means less force.
It is the big forcethat
causes bad injuries
Cars have crumple zones
Unit P2: Physics for your future
4.8 Investigate how crumple zones can be used to reduce the forces
in 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 inwatts, 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 perkilogram) 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 thedependence of braking distance
for a vehicle on initialvelocity squared
(work done to bring a vehicle to rest
equals its initial kinetic energy)
Example
These 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 5
Nuclear fission and nuclear fusion
5.1 atomic (proton) number = bottom number = number of protons
mass (nucleon) number = top number = number of protons + neutrons
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 agamma ray is electromagnetic radiation
5.5 Compare alpha, beta and gamma radiations in terms of theirabilities to penetrate and ionize (ionize = knock electrons off atoms)
5.6 Nuclear reactions can be asource 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 nucleiand 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 energy
and MORE neutrons etc etc
5.9 The chain reaction is controlled
in a nuclear reactorusing
moderators and control rods
moderators: slow down fast moving neutrons so
they can be absorbed by nucleus
control rods: absorb neutrons = reduces reaction
5.10 In a nuclear power station,
thermal (heat) energy from the
chain reaction is used to heat water. The
water turns to steam, the steam turns a turbine.
The turbine turns a generator. Generator generates
electricity.
5.11 The products of nuclear fission are radioactive
5.12 Nuclear fusion is the creation of larger nuclei from
smaller 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 low
temperatures and pressures, due to electrostatic
repulsion of protons. The temperatures need to be
high so the nuclei are going fast enough to overcome
the repulsive electrostatic force.
5.15 It is very difficult and expensive to maintain the high temperatures
needed for fusion. It is thereforevery difficultto make a fusion power station – it could be many years until it happens.
5.16 New scientific theories, suchas ‘cold fusion’, are not accepted until they have been validated
by 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 byradon 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 overtime
nit P2: Physics for your future
6.5 The unit of activity of a radioactive isotope is theBecquerel, Bq
6.6 The half-life of a radioactive isotope is the time taken
for half the undecayed nuclei to decay
6.7 Use the concept of half-life to carry out simple calculationson the decay of a radioactive isotope, including graphicalrepresentations
6.8 Investigate models which simulate radioactive decay
6.9 Dangers of ionizing radiation: tissue damage
and possible mutations. A mutation is a change in
DNA which can lead to cancer.
People working with radiation wear
protective clothing and hold radioactive sources
with tongs.
6.10 Describe how scientists have changed their ideas of radioactivityover time, including:
a the awareness of the hazards associated with radioactivesources: 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 ofnuclear waste
Nuclear waste comes in 3 types:
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)
Possible disposal methods:
Method of disposal / ProblemsFiring into space / Launch vehicle could explode / fall back to Earth, spreading radiation over wide area
Dumping at sea in barrels / Barrels can corrode and release radiation materials into sea which would get into food chains
Storage underground / Site needs to be geologically stable ie low risk of earthquakes
6.12 Evaluate the advantages and disadvantages of nuclear powerfor generating electricity, including the lack of carbon dioxideemissions, risks, public perception, waste disposal and safety issues