## Fission Power Station

Posted in AQA GCSE P2, P2: Nuclear Fission and Fusion by Mr A on 9 Mar 2010
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## Nuclear Fission

Posted in AQA GCSE P2, P2: Nuclear Fission and Fusion by Mr A on 2 Mar 2010
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## Mains Electricity: safety

Posted in AQA GCSE P2, P2: Mains Electricity by Mr A on 1 Mar 2010

• Electricity is dangerous!
• Structure of cables
• Fuses
• Earth wire
• Three-pin plugs

Electricity is dangerous!

An electric shock can affect your muscles and nerves; it can paralyse you or stop your heart beating. You can get an electric shock from anything plugged in to the mains.

Structure of cables

Wires are coated in plastic for safety. The metal wires allow a current to flow as they conduct electricity. The plastic coating is an insulator which prevents people from being electrocuted.

Fuses

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Earth wire

The most dangerous thing that can go wrong with an appliance is that the live wire becomes loose inside and touches the casing. If the casing is metal it will become live. If you touch the casing, you will get an electric shock.

The earth wire is connected to the inside of the casing. Then, if the live wire touches the casing, charge will flow through the earth wire (rather than you), and the fuse will blow.

Three-pin plugs

## Series and Parallel Circuits

Posted in AQA GCSE P2, P2: Current Electricity by Mr A on 8 Feb 2010

• Series circuits
• Parallel circuits

Series Circuits

Components in series are connected along a single path running around the circuit.

Current, I: The same current flows through all the components, and through each point in the circuit.

Voltage, V: This is shared between the components. There is a higher voltage across components with a greater resistance.

Resistance, R: The total resistance of components in series is equal to the sum of their separate resistances.

Parallel Circuits

In a parallel circuit the path splits at some point. This means that some current flows one way, and some the other.

Current, I: Whenever a charge flows into one junction, the same amount must flow out of it. This means that the current through the whole circuit is the sum of the currents through each separate component.

Voltage, V: This is the same across all components that are in parallel with one another.

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## Impulse, Force and Momentum

Posted in AQA GCSE P2, P2: Momentum by Mr A on 7 Feb 2010

• Force and momentum
• Impulse = change in momentum
• Force and impulse
• Examples

Force and Momentum

Physicists often say “momentum is conserved”. However, this is not always the case. It is only true of there is no external force acting.

If there is an external force acting on an object, then the momentum of that object is not conserved, it is changing.

Impulse = Change in Momentum

The word impulse means the change in momentum. In Physics, we use the greek symbol Δ (“Delta”) to mean “change in”, so

Δp = “change in momentum” = impulse

Force and Impulse

The external force acting on an object is related to the impulse given to the object by:

$F = \frac{\Delta p}{t}$

where

• F = force (Newtons, N)
• Δp = impulse = change in momentum (kgm/s or Ns)
• t = time (seconds, s)

Worked Examples

1. A 2000kg car is travelling at 60mph (27m/s) crashes into a wall. The impact lasts 0.02s. What force does the wall exert on the car?
2. What force does a passenger experience if his mass is 70kg?
3. Suppose the car has a much better crumple zone, and the passenger wears his seatbelt, such that the impact time is reduced to 0.6s. What force would he experience then?

## Momentum and Collisions

Posted in AQA GCSE P2, P2: Momentum by Mr A on 2 Feb 2010

• Conservation of momentum
• Collisions
• Explosions

Conservation of momentum

The conservation of energy is a very important thing in Physics. However, energy is not the only thing that is conserved.

Unless a force is acting, momentum is also conserved. This means that the total momentum before something happens will be equal to the total momentum after that thing happens.

Collisions: example

A bus and a car are each travelling at 40mph, but in opposite directions. When they collide the car remains in contact with the bus, and they both continue at 15mph in the direction the bus was travelling. If the car’s mass is 2000kg, what is the mass of the bus?

Explosions: example

A cannon, initially stationary, fires a 15kg cannonball at 200m/s. If the cannon itself has a mass of 1500kg, with what speed does it recoil?

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## IV Plots

Posted in AQA GCSE P2, P2: Current Electricity by Mr A on 1 Feb 2010
• What are IV plots?
• What does the gradient tell us?
• Recognising curves

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## Momentum

Posted in AQA GCSE P2, P2: Momentum by Mr A on 31 Jan 2010
• What is momentum?
• Applying formula
• Examples

Momentum is a measure of how hard it is to stop something: if an object has a lot of momentum, it will be hard to stop it; if its momentum is low, it will be easy.

How much momentum do the following things have? “Loads”, or “not much”?

Momentum Equation

$p = mv$

• p = momentum, $kg ms^{-1}$ or $Ns$
• m = mass, $kg$
• v = velocity, $ms^{-1}$

Worked Examples

1. What is the momentum of a 70kg person running at 5m/s?
2. How fast is that same person going if they have a momentum of 210Ns?

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