Electric circuits

S.MORRIS 2006
ELECTRICAL CIRCUITS
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The CELL
The cell stores chemical energy and transfers it to electrical energy when a circuit is connected.
When two or more cells are connected together we call this a Battery.
The cells chemical energy is used up pushing a current round a circuit.
What is an electric current?
An electric current is a flow of microscopic particles called electrons flowing through wires and components.
+
-
In which direction does the current flow?
from the Negative terminal to the Positive terminal of a cell.
simple circuits
Here is a simple electric circuit. It has a cell, a lamp and a switch.
To make the circuit, these components are connected together with metal connecting wires.
cell
lamp
switch
wires
simple circuits
When the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around.
If there were any breaks in the circuit, the current could not flow.
circuit diagram
cell
switch
lamp
wires
Scientists usually draw electric circuits using symbols;
circuit diagrams
In circuit diagrams components are represented by the following symbols;
cell
battery
switch
lamp
motor
ammeter
voltmeter
buzzer
resistor
variable resistor
types of circuit
There are two types of electrical circuits;
SERIES CIRCUITS
PARALLEL CIRCUITS
The components are connected end-to-end, one after the other.
They make a simple loop for the current to flow round.
SERIES CIRCUITS
If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
PARALLEL CIRCUITS
The current has a choice of routes.
The components are connected side by side.
If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.
measuring current
Electric current is measured in amps (A) using an ammeter connected in series in the circuit.
A
measuring current
A
A
This is how we draw an ammeter in a circuit.
SERIES CIRCUIT
PARALLEL CIRCUIT
measuring current
SERIES CIRCUIT
PARALLEL CIRCUIT
current is the same
at all points in the
circuit.
2A
2A
2A
current is shared
between the
components
2A
2A
1A
1A
copy the following circuits and fill in the missing ammeter readings.
?
?
4A
4A
4A
3A
?
?
1A
?
3A
1A
1A
measuring voltage
The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter
V
Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current.
measuring voltage
Unlike an ammeter a voltmeter is connected across the components
Scientist usually use the term Potential Difference (pd) when they talk about voltage.
measuring voltage
V
This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT
PARALLEL CIRCUIT
V
V
measuring voltage
V
V
V
series circuit
1.5V
voltage is shared between the components
1.5V
3V
voltage is the same in all parts of the circuit.
3V
parallel circuit
3V
3V
measuring current & voltage
copy the following circuits on the next two slides.
complete the missing current and voltage readings.
remember the rules for current and voltage in series and parallel circuits.
measuring current & voltage
V
V
6V
4A
A
A
a)
measuring current & voltage
V
V
6V
4A
A
A
A
b)
answers
3V
3V
6V
4A
4A
6V
6V
6V
4A
4A
2A
2A
4A
a)
b)