Electrical CircuitsElectrical Circuits Electric currentElectric current When river water moves, we say that a When river water moves, we say that a

current of water flows. And when electric charges move in a wire, current of water flows. And when electric charges move in a wire, we say that an electric current flows. We measure current in Amps we say that an electric current flows. We measure current in Amps (A)(A)

Voltage Voltage the difference in height between the start and end of the difference in height between the start and end of the river is like the voltage. If the difference is large, the voltage the river is like the voltage. If the difference is large, the voltage will be large. We measure voltage in Volts (V)will be large. We measure voltage in Volts (V)

Resistance Resistance this can be like the number of obstacles in the this can be like the number of obstacles in the river that make it hard to flow. We measure resistance in Ohms river that make it hard to flow. We measure resistance in Ohms (Ω) (Ω)

charges move round a circuit. They move from one side of charges move round a circuit. They move from one side of a cell or battery, through the wires and components such as a cell or battery, through the wires and components such as lamps, and then into the other side of the battery. lamps, and then into the other side of the battery.

Circuit diagramsCircuit diagrams We use circuit diagrams so we don’t have to be We use circuit diagrams so we don’t have to be

artists! We draw them with a pencil and ruler.artists! We draw them with a pencil and ruler.

Can you name these symbols?

Answers….Answers….

Series circuitsSeries circuits A television series is one program A television series is one program

after another. A series circuit is after another. A series circuit is similar. If you follow the circuit, similar. If you follow the circuit, starting at the cell, it will go starting at the cell, it will go through several components but through several components but lead straight back to the celllead straight back to the cell..

The problem is, if one component The problem is, if one component breaks the circuit is broken. eg. breaks the circuit is broken. eg. cheap xmas tree lights….ask grown cheap xmas tree lights….ask grown ups!ups!If you put more lamps into a series circuit, the lamps will be dimmer than before.

Parallel circuitsParallel circuits

In a parallel circuit, if a In a parallel circuit, if a lamp 'blows' or a lamp 'blows' or a component is component is disconnected from one disconnected from one parallel wire, the parallel wire, the components on components on different wires keep different wires keep working. Unlike a working. Unlike a series circuit, the series circuit, the lamps staylamps stay brightbright if if you add more lamps in you add more lamps in parallel parallel

Measuring currentMeasuring current

We use an ammeter to measure We use an ammeter to measure currentcurrent

The current is the same everywhere in a series circuit. It does not matter where you put the ammeter, it will give you the same reading

The current in a The current in a series circuit series circuit

depends upon the depends upon the number of cells. The number of cells. The more cells you add, more cells you add,

the greater the the greater the currentcurrent

The current is not used The current is not used up by the components in up by the components in a circuit. This means that a circuit. This means that the current is the same the current is the same anywhere in a series anywhere in a series circuit, even if it has lots circuit, even if it has lots of lamps or other of lamps or other components. components.

Measuring VoltageMeasuring Voltage Voltage is a measure of the difference Voltage is a measure of the difference

in electrical energy between two parts in electrical energy between two parts of a circuit. of a circuit.