Download Metaphor circuits

ELECTRICAL CIRCUITS
All you need to be an inventor is a good
imagination and a pile of junk.
-Thomas Edison
I=V/R
I
= Current (Amperes) (amps)
V
= Voltage (Volts)
R
= Resistance (ohms)
George Simon Ohm (1787-1854)
Think about electric circuits as:
Circuit: is a route for electrons to
flow. The path is from a power
source with a negative terminal
through the various comments
and on to a positive terminal.
Think of it as a circle. The paths may split off
here and there but they always form a line
from negative to positive.
Think about electric circuits as:
Voltage: a force that pushes
the current through the
circuit (in this picture it
would be equivalent to
gravity)
Think about electric circuits as:
Resistance: friction
that impedes flow of
current through the
circuit (rocks in the
river)
Think about electric circuits as:
Current: the actual
“substance” that is
flowing through the
wires of the circuit
(electrons!) The rate of
flow of an electric
charge through a
conductor.
Think about electric circuits as:
Conductor: is a material (usually a metal such
as copper) that allows electrical current to
pass easily through one point to another. The
current is made up of electrons.
This is opposed to an insulator which
prevents the flow of electricity through it.
Can you think of other conductors? Can you think of possible
insulators?
Use the ammeter and voltmeter to make your discoveries.
Record you findings.
Would This Work?
Would This Work?
Would This Work?
The Central Concept: Closed Circuit
Scientists
symbols:
cell
Circuit Diagram cuits using
lamp
switch
wires
Simple Circuits
• Series circuit
– All in a row
– 1 path for electricity
– 1 light goes out and
the circuit is broken
• Parallel circuit
– Many paths for electricity
– 1 light goes out and the
others stay on
1
2
3
Since the brightness of the bulbs indicates how
much current is flowing in the circuit, write a
statement which describes what happens to the
current in a series circuit as you add more resistors
to the circuit.
The current decreases because the resistance increases. Ohm’s
Law says that I=V/R. The voltage in the system is constant,
resistance increases.
PARALLEL CIRCUIT
• Place two bulbs in parallel. What do you
notice about the brightness of the bulbs?
• Add a third light bulb in the circuit. What
do you notice about the brightness of the
bulbs?
• Remove the middle bulb from the circuit.
What happened?
measuring current
Electric current is measured in amps (A) using
an ammeter connected in series in the circuit.
A
measuring current
This is how we draw an ammeter in a circuit.
A
SERIES CIRCUIT
A
PARALLEL CIRCUIT
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
measuring voltage
This is how we draw a voltmeter in a circuit.
V
SERIES CIRCUIT
V
PARALLEL CIRCUIT
OHM’s LAW
• Measure the current and voltage across each circuit.
• Use Ohm’s Law to compute resistance for a Series Circuit
Voltage
Current
Resistance
Parallel Circuit
Voltage
Current
Resistance
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
Fill in the missing ammeter readings.
3A
?
4A
?
3A
1A
?
4A
?
4A
1A
1A
?
The circuit is no longer complete, therefore current can not flow.
The voltage decreases because the current is decreased
and the resistance increases.
The current remains the same. The total resistance drops in a
parallel circuit as more bulbs are added
The current increases.
Series and Parallel Circuits
• Series Circuits
– only one end of each component is connected
– e.g. Christmas tree lights
• Parallel Circuits
– both ends of a component are connected
– e.g. household lighting
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