Download Static electricity Insulated materials can become electrically charges

Static electricity
Insulated materials can become electrically charges. The electricity can’t move
away. This is called electrostatic charge.
Rubbing materials together, electrons get transferred from one object to
another.
One object becomes positively charged if the electrons are removed.
The other object becomes negatively charged as it gains the electrons.
The charged materials attracted towards oppositely charged materials.
Objects with the same charge are repelled from each other.
Static electricity as good points and bad points.
Bad points
Lightning can damage houses. Lightning occurs when clouds build up an electric
charge.
Electric shock from escalators or trolleys
Cars, trains, aeroplanes build up electric charge. If a spark occurs near the fuel
it can explode.
Good points.
Spraying vehicles or objects. The paint is one charge and the thing being
painted is another charge. The object gets an even coating of paint as the paint
particles repel each other and spread out.
Static electricity can help reduce soot/particles in smoke. The particles can
become charged and the inside of the smoke stack is the opposite charge. The
particles get attracted to the side.
Photocopies use static electricity to put the image on the paper.
Radiation
The structure of the atom contains a nucleus and shells of electrons that go
around the nucleus.
The nucleus contains protons and neutrons.
Particle
Relative Charge
Relative Mass
Electron
-1
0.0005 (zero)
Proton
+1
1
Neutron
0
1
Mass number
12
C
Atomic number
6
The atomic number is the number of protons in an atom (and remember, n˚ of
protons = n˚ of electrons).
The mass number = number of protons + number of neutrons
The number protons tell you which element it is.
The number of neutrons can change.
Elements with different number of neutrons are called isotopes.
Radioactive isotopes are unstable compounds that emit radiation.
There are three different types of radiation.
Alpha is a particle which contains two protons and two neutrons, this can be
stopped by card, and it doesn’t travel far into an object
Beta is a particle that is an electron, it is stopped by sheets of aluminium. This
can travel further than alpha particles.
Gamma is a wave. Gamma rays can travel very far through an object. Lead can
stop the movement of them.
Chain reaction
If an atom is hit by a neutron it can cause the atom to release two or more
neutrons. These neutrons can hit another atom and release more neutrons. This
can continue and continue. This is called Nuclear Fission.
In nuclear power plants or military ships, this nuclear fission process is
controlled and large amounts of heat energy is released.
Nuclear fusion is different. This is when two atom join together to form a new
atom. This is how our sun is releasing energy
Momentum and work done.
Momentum is calculated using the following equation which will be given in your
exam
Momentum = mass x velocity
If you are not wearing a seat belt in a car that has an accident then your
momentum carries on but the car stops and you go through the window screen.
Momentum is conserved. The momenta before something happens is equal to the
momenta afterwards.
Work done is calculated using the following equation which will be given in your
exam
Work done = force x distance moved
W
= F
x d
[Joules,J]
[N]
[Metres,m]
Forces
Kinetic energy is the scientific name for movement energy.
Elastic potential energy is energy stored in an object when it has changed shape.
E.g. elastic band being pulled apart.
Forces are measured in Newtons (N)
Arrows on diagrams show which way the force is being applied.
If two forces are applied to an object and they are the same size, these are
called balanced.
If two forces are applied to an object and they are not equal size then these
are called unbalanced.
If there is more than one force acting on an object in one direction this is called
the resultant force.
You will be given the equations in your exam to work out
resultant force= mass x acceleration
[Newton, N]
[Kg]
[m/s2]
Weight = mass x gravitational field strength
W
[N]
= m
x
[Kg]
g
[N/kg]
As a result of this last equation if your mass is big then your weight is also big
or if the gravitational field strength is big then you also weigh more. The
reverse also applies.
Electricity and work done.
Circuits are either series or parallel.
Conductors allow electricity to flow through them.
Charge is measured in coulomb (C)
The equation will be given in your exam
Charge = current x time
[C]
[A]
[s]
Ammeters measure current in amps (A). They are placed in series in a circuit.
Voltmeters measure potential difference in volts (V). They are placed in
parallel in a circuit.
Resistance is how difficult the electricity finds, to travel through the circuit.
Potential difference = current x resistance
[V]
[A]
[ohm, Ω]
Resistance can be changed by using a variable resistor.
Resistance is affected by heat. The hotter the wire the lower the resistance.
These devices are called thermistor.
Resistance of a light dependent resistor decreases as light intensity increases.
Rule 1 In a series circuit the current is the same at any point in the circuit.
Rule 2 The total resistance in a series circuit is the sum of the resistance of all
the components in the circuit.
Rule 3 In a parallel circuit the currents through each branch adds up to the
total current from the cells.
Rule 4 The potential difference provided by cells connected in series is the sum
of the potential differences of all the cells, as long as they are all connected
the same way around.
Rule 5 In a series circuit the potential difference is shared between the
components in the circuit.
Rule 6 In a parallel circuit the potential difference is the same across each
route.
AC current is an alternating current. This means that the current flows in both
directions. Mains electricity uses AC current. In the UK it travels at 50 Hz.
DC current is a direct current. This means that the current flows in one
direction. Batteries us DC current
Plugs have three wires. Brown is live and is attached to the fuse on the right.
The blue wire is neutral and is found on the left. Electricity flows through
these two wires.
A plug also has an earth wire. This is green and yellow and found at the top of
the plug. This is for safety purposes.
Fuses control how much current flows through it. A 3 amp fuse will only allow a
current of below 3 amps go through it. Anything over this the fuse will blow and
will stop working.
Power is the number of joules transferred by an appliance. It is measure in
watts (W).
You will be given the equation for working out power.
Power (watts,W) = energy (joules,J) ÷ time (seconds,s)
Or
Power(watts,W) = current (amps,A) x potential difference (volts,V)
Acceleration
Acceleration is calculated using the following equation which will be given in your
exam.
Acceleration = change in velocity ÷time taken for the change.
Acceleration is measure in m/s2
You will be asked to interpret graphs for these question.
Stopping distances.
When stopping an object two things has to happen
Thinking distance- the time taken for you to think about stopping.
Stopping distance – is the physical thing.
A number of things affect how quickly a car or object can stop.
The road conditions
How good the brakes are.
Speed of object