Download How you should be thinking about electric circuits

ELECTRICAL CIRCUITS
All you need to be an inventor is a good
imagination and a pile of junk.
-Thomas Edison
1
What is it?
2
• The movement
of electrons through a conductive material
What is it?
• Electrons bump into other electrons in adjacent shells (called
valence shells) and continue down the path
3
Electrons will
only flow if there
is a complete
circuit for them
to flow around
• Electrons, which are negatively charged, emerge from the
negative terminal of the power supply
• Conventional notation, however, is to refer to the electricity as
emitting from the positive terminal of the power supply
4
RESISTANCE CURRENT
How you should be
thinking about
electric circuits:
Voltage
the “speed”, and subsequent
force, that pushes the current
through the circuit
Water analogy
The higher the water fall the
more “voltage”
5
VOLTAGE
CURRENT
How you should be
thinking about
electric circuits:
Resistance
friction that impedes flow of
current through the circuit
Water analogy
rocks in the river
6
VOLTAGE RESISTANCE
How you should be
thinking about
electric circuits:
Current
The actual “substance” that is
flowing through the wires of the
circuit (electrons!)
Water analogy
The water molecules
7
UNDERSTANDING
ELECTRICITY
• Air is conductive…if you have enough voltage to push
the electrons through it (i.e. – lightening)
• 10,000 volts might not hut you…but if it pushes just 1
amp of current through your heart it can be fatal
• If the circuit has no resistance, it’s called a short circuit
and infinite current will flow until the circuit fails (i.e. –
melts or depletes)
8
Ohm’s Law
V=IxR
I = Current (Amperes) (amps)
V = Voltage (Volts)
Georg Simon Ohm (1787-1854)
R = Resistance (ohms)
9
Ohm’s Law
V=IxR
• So more voltage will
provide you more current
Georg Simon Ohm (1787-1854)
• And more resistance will
provide you less current
10
Simple Circuits
• Parallel circuit
– Many paths for
electricity
– 1 light goes out and the
others stay on
• Series circuit
– All in a row
– 1 path for electricity
– 1 light goes out and the
circuit is broken
11
ELECTRICAL CIRCUITS
Measurements
12
Measuring current
This is how we draw an ammeter in a circuit.
A
A
SERIES CIRCUIT
PARALLEL CIRCUIT
13
Measuring current
SERIES CIRCUIT
• Current is the same
2A
at all points in the
circuit.
2A
2A
PARALLEL CIRCUIT
• Current is shared
between the
components
2A
2A
1A
1A
14
Measuring current
Fill in the missing ammeter readings.
3A
?
4A
?
3A
1A
?
4A
?
4A
1A
1A
?
15
Measuring voltage
This is how we draw a voltmeter in a circuit.
V
SERIES CIRCUIT
V
PARALLEL CIRCUIT
16
Measuring voltage
Series Circuit
Voltage is shared between the components
6V
3V
3V
Like a
train
running
through
brick walls
17
Measuring voltage
Parallel Circuit
Voltage is the same in all parts of the circuit.
3V
3V
3V
Like two
people
under the
same
waterfall
18
Review
a)
6V
4A
A
V
V
A
19
Review
b)
4A
6V
A
V
A
V
A
20
Review
Answers
a)
b)
4A
6V
4A
4A
3V
6V
4A
6V
2A
3V
4A
6V
2A
21