electrical circuits all you need to be an inventor is a good imagination and a pile of junk. -thomas...
TRANSCRIPT
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ELECTRICAL CIRCUITS
All you need to be an inventor is a good imagination and a pile of junk.
-Thomas Edison
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OHM’S LAW
I = V / R
Georg Simon Ohm (1787-1854)
I = Current (Amperes) (amps)
V = Voltage (Volts)
R = Resistance (ohms)
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How you should be thinking about electric circuits:Voltage: a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)
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Resistance: friction that impedes flow of current through the circuit (rocks in the river)
How you should be thinking about electric circuits:
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Current: the actual “substance” that is flowing through the wires of the circuit (electrons!)
How you should be thinking about electric circuits:
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WOULD THIS WORK?
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WOULD THIS WORK?
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WOULD THIS WORK?
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THE CENTRAL CONCEPT: CLOSED CIRCUIT
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circuit diagramcircuit diagram
cell switch
lamp
wires
Scientists usually draw electric circuits using symbols;
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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
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1
2
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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?
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PARALLEL CIRCUIT
• Remove the middle bulb from the circuit. What happened?
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measuring current
Electric current is measured in amps (A)
using an ammeter connected in series in
the circuit.
A
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measuring current
A A
This is how we draw an ammeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
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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
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measuring voltage
V
This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
V
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measuring currentSERIES CIRCUIT
PARALLEL CIRCUIT
• current is the same
at all points in the
circuit.
2A 2A
2A
• current is shared between the components
2A2A
1A
1A
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fill in the missing ammeter readings.
?
?
1A
1A
1A
3A?
?
1A
?
3A
1A
1A
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The circuit is no longer complete, therefore current can not flow
The voltage decreases because the current is decreased
and the resistance increases.
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The overall current increases. The total resistance drops in a parallel circuit as more bulbs are added. The individual current remains the same.
The current increases.
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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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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.
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series circuit
1.5V
• voltage is shared between the components
1.5V
3V
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• voltage is the same in all parts of the circuit.
3V
parallel circuit
3V
3V
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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.
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measuring current & voltage
V V
6V4A
A
A
a)a)
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measuring current & voltage
V
V
6V4A A
A
A
b)b)
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answers
3V 3V
6V
4A 4A6V
6V
6V4A 4A
2A
2A
4A
a)a) b)b)