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20.1 Electric Circuits pp. 730 - 735 Mr. Richter

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Agenda Warm-Up Notes: Circuit Diagrams Electrical Circuits and Short Circuits Using the Multimeter

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Objectives: We Will Be Able To… Draw and interpret circuit diagrams. Build a circuit given a circuit diagram. Use the multimeter to measure voltage and current in a circuit.

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Warm-Up: At your table, use the whiteboard to draw a circuit that contains: 1 light bulb 1 resistor 1 open switch 2 batteries When you are finished, bring your whiteboard to the front of the room.

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Schematic Diagrams

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Schematic diagrams, often called circuit diagrams, are used to represent the design of electrical circuits. Like force diagrams represent forces.

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Electric Circuits

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An electric circuit is a path through which electricity can be conducted. All circuits contain two parts: a potential difference: what supplies the energy (voltage) a load: an element or group of elements that uses the energy Conservation of energy: the voltage (energy in) must equal the load (energy out.

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Electric Circuits Switches are used to turn electricity on and off. If a switch is on (connected), the circuit is closed, and electricity is flowing. If a switch is off (unconnected), the circuit is open, and the flow of electricity is stopped. Also happens with broken devices.

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Electric Circuits A short circuit is a path (often accidental) in a circuit that has a resistance close to zero. Low resistance means high current. High current means lots of extra heat. Extra heat can mean: melting burning exploding DANGER!

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Electric Circuits To prevent wires from drawing too much current (short circuiting) we use: Circuit Breakers – flips the switch to off when the current gets too high Fuses – actually breaks when current is too high

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Measuring Voltage and Current

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At your table, build the circuit below. When you’re done, check in with Mr. Richter

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Measuring Voltage A multimeter is used to measure voltage, current and resistance in a circuit. To measure voltage: set the multimeter to Volts. Red lead in the middle. Touch probes to either side of an element to see the voltage gain or drop. Red lead is always more “downstream.” Voltage is a difference in potential energy. If energy is gained from black to red, voltage should be positive. Energy lost = negative voltage No change in energy = 0 volts.

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Measuring Current To measure current: set the multimeter to mAmps Red lead on the left. Current is always positive! You must run your circuit THROUGH the multimeter. It counts how many electrons pass by, like a ticket counter.

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Wrap-Up: Did we meet our objectives? Draw and interpret circuit diagrams. Build a circuit given a circuit diagram. Use the multimeter to measure voltage and current in a circuit.

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Homework p. 735 #1-5

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