# P5 revision

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- Created by: Harry Ward
- Created on: 18-03-11 20:23

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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

- The sum of the coltage for each component is equal to the voltage across the cell
- .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…

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