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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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What is it?

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What is it?• The movement of electrons through a conductive material• Electrons bump into other electrons in adjacent shells (called

valence shells) and continue down the path

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• 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

Electrons will only flow if there

is a complete circuit for them to flow around

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How you should be thinking about electric circuits:

Voltagethe “speed”, and subsequent force, that pushes the current through the circuitWater analogyThe higher the water fall the more “voltage”

VOLTAGE RESISTANCE CURRENT

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How you should be thinking about electric circuits:

Resistancefriction that impedes flow of current through the circuitWater analogyrocks in the river

VOLTAGE RESISTANCE CURRENT

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How you should be thinking about electric circuits:

CurrentThe actual “substance” that is flowing through the wires of the circuit (electrons!)Water analogyThe water molecules

VOLTAGE RESISTANCE CURRENT

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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)

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Ohm’s Law

V = I x R

Georg Simon Ohm (1787-1854)

I = Current (Amperes) (amps)

V = Voltage (Volts)

R = Resistance (ohms)

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Ohm’s Law

V = I x R

Georg Simon Ohm (1787-1854)

• So more voltage will provide you more current

• And more resistance will provide you less current

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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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ELECTRICAL CIRCUITS

Measurements

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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 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.

?

?

4A

4A

4A

3A?

?

1A

?

3A

1A

1A

Measuring current

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Measuring voltage

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUITV

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3V

Series Circuit

Voltage is shared between the components

3V

6V

Measuring voltage

Like a train running through brick walls

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Parallel Circuit

Voltage is the same in all parts of the circuit.

3V

3V

3V

Like two people under the same waterfall

Measuring voltage

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Review

V V

6V4A

A

A

a)

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V

V

6V4A A

A

A

b)

Review

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ReviewAnswers

3V 3V

6V

4A 4A6V

6V

6V4A 4A

2A

2A

4A

a) b)