Electricity

• Current is the flow of electrical charge
• Charge will only flow around a closed circuit
• Charge is measured in amperes (amps, A)
• The size of the current depends on the rate of flow of charge. 
• Current is measured using an ammeter connected in series!​

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  Q = It​

  Charge = current x time
• Charge is measured in coulombs, C
• Potential difference is shared across is components in a series circuit.
• Potential difference is the same across all components in a parallel circuit.
• In a series circuit, current is the same everywhere
• Current is shared across all components in parallel circuits.
• Resistance in series


  Total resistance is the sum of the resistance across components
• Resistance in parallel


  If you add two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors
• In series circuits, electrical components are connected one after another in a single loop.​

  An electron will pass through every component on its way round the circuit.
• If one of the bulbs is broken, then current will not be able to flow round the circuit. If one bulb goes out, they all go out.​

  Series circuit
• In parallel circuits, electrical components are connected alongside one another, forming extra loops.​

  An electron will not pass through every component on its way round the circuit.
• If one of the bulbs is broken, then current will still be able to flow round the circuit through the other loop. If one bulb goes out, the other will stay on.​

  Parallel circuit
• Potential difference is the difference in energy the electrons have between two different points in a circuit. It is also described as the driving force that pushes the charge around.
• Potential difference can also be called voltage and is measured in volts, V.
• To measure potential difference we use a voltmeter, that has to be connected in parallel across the component in order to measure the difference in energy!​
• V = IR​

  Voltage = current x resistance
• Series circuits only have a single loop, whereas parallel circuits have more than one loop. In a series circuit, the potential difference is shared between components and the current is the same everywhere. In a series circuit, components with a greater resistance will always have a greater share of voltage. Adding another resistor in parallel will decrease the total resistance.
• V = E/Q

  Voltage = energy/charge
• Resistance is caused by anything that opposes the flow of electrical charge. It is measured in ohms.
• Increasing or decreasing the potential difference of the circuit will affect the current.
• Plotting current-resistance results for different wires tells us about the resistance of these wires. The steeper the line, the lower the resistance of the wire.
• 3 factors affecting resistance of a wire

  length of wire

  thickness of wire

  temperature
• length of wire affecting resistance:

  the resistance of a wire is affected by length. resistance of a long wire is greater than that of a short wire because the electrons collide with more metallic nuclei as they pass through
• thickness of wire affecting resistance:

  the resistance of a thin wire is greater than the resistance of a thick wire because a thick wire because a thin wire has fewer electrons to carry the current.
• temperature affecting resistance:

  as temperature increases the metal nuclei begin to vibrate more. the electrons will have more chance of colliding and so resistance increases.
• Electrical current is not the flow of electrons; it is the flow of charge! As charge can be positive or negative then naturally, current is in the direction of positive charge flow and in the opposite direction to negative charge flow.
• Ohmic conductors have a constant resistance
• The resistance of ohmic conductors does not change with current. At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it.
• The resistance of some resistors and components does change (e.g. a diode or filament lamp).
• When an electrical charge flows through a filament lamp, it transfers some energy to the thermal energy store of the filament, which is designed to heat up. Resistance increases with temperature, so as current increases, the filament lamp heats up more and the resistance increases.
• For diodes, the resistance depends on the direction of the current. They will happily let current flow in one direction, but have a very high resistance when reversed.
• Adding resistors in series increases the total resistance of the circuit
• When you add resistors in parallel, the total current increases, meaning total resistance decreases. The more resistors you add, the smaller the overall resistance.