# P2 summary.

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• Created by: Abbs11_
• Created on: 02-05-16 15:09
• PHYSICS 2.
• Static and current electricity.
• To stop electrostatic charge building up we can connect the charged object to the ground - this is called earthing.
• Earthing provides an easy route for the static charges to travel into the ground.
• This means no charge can build up to give you a shock or make up a spark.
• Current is the rate of flow of charge around a circuit.
• In the metal wires of a circuit, this charge is carried by electrons.
• Charge (Q)  = current (I)  x time (T)
• Controlling and using electric current.
• Current - the rate of flow of charge around the circuit.
• Unit = ampere, A
• Voltage - the driving force that pushes the current round.
• Unit = volt, v. can also be called potential difference.
• Potential difference (V) = current (I) x resistance (R)
• Resistance - is anything in the circuit which slows down the flow.
• Unit = ohm
• If you increase the resistance, then less current will flow.
• If you increase the voltage then more current will flow.
• Electrical power (P) = potential difference (V) x current (I)
• Energy transferred (E)  = current (I) x potential difference (V) x time (T)
• Light dependant resistor (LDR) changes its resistance depending on how much light there is.
• In bright light, the resistance falls.
• In darkness, the resistance is highest.
• Thermistor (temp dependant resistor.)
• like an LDR  but its resistance depends on temperature.
• In hot conditions the resistance drops.
• In cold conditions, the resistance goes up.
• Motion and forces.
• Speed - how fast you're going,
• Speed  (S) = distance (D) / time (T)
• Velocity - how fast in a specific direction.
• Acceleration - is how quickly the velocity is changing.
• This could be change in speed.
• Or change in direction.
• Or both.
• Acceleration (A) =      change in velocity  (V-u)   / time taken (T)
• When two forces interact they exert a force on each other.
• If object A exerts a force on object B then object B exerts the exact opposite force on object A.
• Resultant force.
• Force (F) = mass (M) acceleration (A)
• The bigger the resultant force, the greater the acceleration or deceleration.
• The bigger  the mass of the object, the smaller the acceleration.
• To get a big mass to accelerate as fast as a small mass it needs a bigger resultant force.
• Momentum, energy, work and power.
• The greater the mass of an object and the greater its velocity the more momentum the object has.
• Momentum(Kg m/s) = Mass (Kg) x velocity       ( m/s)
• When a force acts on an object, it causes a change in momentum.
• Force (N) = change in momentum(Kg m/s) / time (S)
• When a force moves on an object, energy is transferred and work is done.
• Work done (E) = Force (F) x distance moved in the direction of the force (D)
• Power is  something transfers a lot of energy in a short space of time.
• Power  (P)  = work done (E) / time taken (T)
• Energy can never be created nor destroyed - only transferred from one form to another.
• Energy is only useful when its transferred from one form to another.
• Nuclear fission and nuclear fusion.
• Ionisation.
• Atoms can gain or lose electrons. When an atom (with no overall charge) loses or gains an electron it is turned into an ion (which is charged).
• Nuclear fission.
• A type of nuclear reaction that is used to release energy from uranium or plutonium atoms.
• Nuclear Fusion.
• The opposite to nuclear fission.
• Two light nuclei collide at high speed and join to create a larger nucleu
• More energy is created than fission.
• Only happens at high temperatures and pressure.
• Background radiation - is low level radiation thats around us all the time.
• The half life of a radioactive isotope is the time taken for half of the undecayed nuclei to decay.
• Half-life.
• A short half life means the activity falls quickly because lots of the nuclei decay quickly.
• A long half life means the activity falls more slowly because most of the nuclei don't decay for a long time.
• Uses for: Alpha, Beta, Gamma.
• Alpha.
• Used in smoke alarms.
• Beta.
• Thickness control in paper mills.
• Pros and cons of nuclear power.
• Dangerous.Cant be disposed of safely.
• Very reliable. Not as risky as perceived.
• Doesn't release gases such as sulphur dioxide - so clean source of energy
• Huge amounts of energy created from small amount of nuclear material.
• However cost of the nuclear power plant is very expensive.

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