# Physics III

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Electricity

Key words

- Current is the flow of electrons around a circuit

- Potential difference is the voltage difference between two points

- Resistance is something in a circuit which slows down the flow of current

- Charge is HOW MANY electons flow through a point in the wire in a certain time

Standard test circuit consists of:

-An ammeter to measure current in series

- A voltmeter in paralell to the component to measure the potential difference

- A variable resistor to alter the flow of current through the circuit in order to get a variety of results to plot a V-I graph in series

- A component to test in series

- A cell or battery

In series

- The current is the same all the way around the circuit

- The voltage is shared between components

In paralell

- The current is shared between components

- The voltage is the same all the way around the circuit

- The reistance = voltage/current

Always read the question and find out if it is a series or paralell circuit before you do anything.

Examples of series and paralell

Fairy lights are in series which is good as each bulb has a low current across it as voltage is split between al the bulbs. However if one breaks then they all break.

Cars stereo, heaters, lights are all in paralell so everything can get the full voltage from the battery however if everything is all on at once lights can be seen as dimmer as not everything is able to get the full potential difference from the battery.

Resistance is something that slows down the flow of current in a circuit. This is affected by:

-Temperature, as if the temperature are high the electrons are provided more energy to move around and so are more likely to bump into the atoms of the material of the wire which causes resistance. High temperature = High resistance Low temperature = Low resistance

-Thickness of wire.  A thin wire has more resistance than a thick wire as electrons and atoms are more likely to collide in a thin wire. Thin wire = High resistance Thick wire = Low resistance

- Length of wire. The longer the wire the more electrons are going to bump into atoms as they have further to travel compared…