# P5 revision

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static electricity

Positive charges do not move

• Moving charge=current
• When a van der graff generator runs, charge collects on its dome
• This charge may "jump" in the form of a spark
• Electricity always takes the shortest route to earth. In this case, through you,
• Charges are randomly distibuted across everything
• Rubbing the balloon on your hair generates friction which transfers the negative charges across to the balloon
• The negatively charged ballon is attracted to the positive charges in the wall, so it sticks.

resistance

• Components in a circuit make it harder for the electrons to flow through, they are said to have resistance.
• Resistance is a mesure of how much a material tried to stop electrons passing through it.
• All wires and components have resistance, although the resistance in wires is negligible and can be ignored.
• Electrons passing through a wire with resistance create heat due to the electrons colliding with statiobary metal ions.
• Resistors are components designed to reduce the current of a circuit:
• A variable resistor has a customisable resistance.
• A fixed resistor has a permanent resistance.
• Voltage= current X resistance

Voltage

• Voltage is a mesure of how much "push" the electrons in a circuit get from the power source. The larger the voltage, the larger the push.
• AKA. potential difference
• For a series circuit:
• The sum of the coltage for each component is equal to the voltage across the cell
• I.E. V(cell)= V1 + V2
• .For a parallell circuit, the voltage across each component is the same as the voltage of the cell:
• I.E. V(cell)=V1=V2
• Voltage is "used up" by comentents in series, but if it parallell, the voltage is split but stays the same.
• Voltage= current X resistance

Ohm's law

• This version of ohm's law states that as voltage increases, the current also increases. The voltage and current are directly propotional whilw the resistance remains the same.
• For a low resistance material, more current is allowed to flow for a given voltage. For a high resistance material, less current will