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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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Would This Work?

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The Central Concept: Closed Circuit

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circuit diagram cellswitchlampwires 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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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 CIRCUITPARALLEL CIRCUIT V

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measuring current SERIES CIRCUIT PARALLEL CIRCUIT current is the same at all points in the circuit. 2A current is shared between the components 2A 1A

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fill in the missing ammeter readings. ? ? 4A 3A? ? 1A ? 3A 1A

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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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Current Intensity: The number of charges that flow past a given point in an electrical circuit every second. I = q/ Δt I = current intensity (in A) q= the charge (in C) Δt = the time interval (in s)

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Question What is the charge needed for 1 minute of operation when a car headlight requires a current of 15 A What do we know? I = 15A Δt = 1 min = 60 sec q = ? I = q/Δt q = I x Δt q = 15A x 60sec = 900 C Answer: the charge needed is 900 C

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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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Potential Difference: Is the amount of energy transferred between 2 points in an electrical circuit. V = E/q V = is the potential difference (in V) E = is the energy transferred (in J) q = is the charge (in C)

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Question What is the amount of energy provided by a charge of 200 C and a potential difference of 120 V ? What do we know? V = 120 V q = 200 C E = ? V = E/q E = V x q E = 120 x 200 = 24000 J Answer: the amount of energy is 24000 J (Joules)

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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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Resistance = is the ability of a material to hinder the flow of electric current 4 factors that affect the resistance of a substance to flow FactorDescription Nature of the substance Poor conductors resist current flow more than good conductors LengthThe longer an element or wire, the greater its resistance to current flow DiameterSmaller diameter resists current flow more than a larger diameter TemperatureWarm element usually resists current flow more than a cold element

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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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Question What is the Voltage if the resistance is 30 Ohms and the current intensity is 15 A? R = 30 Ohms I = 15 A V = ? V = R x I = 30 x 15 = 450 V Answer is 450 V

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Question An automobile headlight has an average resistance of 44 ohms. Car batteries provide a potential difference of 22 volts. What amount of current passes through the headlight?

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Answer Resistance = 44 Ohms Voltage (potential difference) = 22 V Current (I) = ? V = R x I I = V / R = 22V / 44 Ohms = 0.5 Amps

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Class Work 1) p. 173 of the textbook Complete questions 10 – 18 2) Website Ohm’s law questions and answers 3) Finish formal lab

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