Download Electric Circuits

Currents CIRCUITS
S.MORRIS 2006
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2 types of electric currents
AC = Alternating current
• Electrons in the circuit move in 1 direction
for some time and then switch directions
and go the opposite way
• Ex: household outlets and appliances
•DC = Direct current
• Charges always flow in the same direction
• From negative to positive
• Ex: batteries
The CELL – the power source
Cells are a type of voltage source that converts
chemical energy into electrical energy when a
circuit is connected.
When two or more cells are
connected together we call this
a Battery.
What is an electric circuit?
Any pathway through which electrons can flow/travel
+
-
The bare essentials for a circuit:
• battery/power source
• Load (lightbulb/lamp)
• Wires
One more piece…
Most circuits also have a switch that is used to turn the
circuit on and off
when the switch is open, it creates a gap so that
electrons cannot flow
when the switch is closed, the circuit is complete
and electrons can move through it
types of circuit
There are two types of electrical circuits;
SERIES CIRCUITS
PARALLEL CIRCUITS
SERIES CIRCUITS
The components are connected end-to-end, one
after the other.
They make a simple loop for the current to flow
round.
A break anywhere in the loop will result in an open
circuit and no more moving electrons
If one bulb ‘blows’ it breaks the whole circuit and
all the bulbs go out.
PARALLEL CIRCUITS
The components are connected side by side.
The current has a choice of routes.
If there is a break in one path, it might not effect the
other path
circuit diagram
Scientists usually draw electric circuits using symbols;
cell
lamp
switch
wires
measuring current
Electric current is measured in amps (A) using an
ammeter which is connected in series in the circuit.
A
measuring current
This is how we draw an ammeter in a circuit.
A
A
SERIES CIRCUIT
PARALLEL CIRCUIT
measuring current
SERIES CIRCUIT
• current is the same
at all points in the
circuit.
2A
2A
2A
PARALLEL CIRCUIT
• current is shared
between the
components
2A
2A
1A
1A
Discuss with your neighbor what the
missing ammeter readings would be
3A
?
4A
?
3A
1A
?
4A
?
4A
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 which is drawn across (on top of) circuit
components
V
measuring voltage
This is how we draw a voltmeter in a circuit.
V
V
V
SERIES CIRCUIT
V CIRCUIT
PARALLEL
series circuit
• voltage is shared between the components
3V
1.5V
1.5V
parallel circuit
• voltage is the same in all parts of the circuit.
3V
3V
3V
Let’s recap:
Series
Circuit
Current
Voltage
Parallel
Circuit
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
a)
6V
4A
A
V
V
A
measuring current & voltage
b)
4A
6V
A
V
A
V
A
answers
a)
b)
4A
6V
6V
4A
6V
4A
4A
3V
2A
3V
4A
6V
2A
measuring resistance in series
In series: to find total resistance of a series circuit, add
the individual resistances of the objects in series
6V
3Ω
2Ω
The total resistance of this circuit would be 5 Ω
What happens to voltage as you move past each light?
-It drops – we can calculate the “voltage drop” of each
light using Ohm’s law
6V
3Ω
2Ω
measuring resistance in parallel
In parallel, use the following formula to find the total
resistance:
6V
6V
3Ω
RT = R1 x R2 =
R1 + R 2
2Ω
Total resistance in parallel will always be less than the
smallest resistor