20.1 Electric Circuitspp. 730 - 735

Mr. Richter

Agenda

Warm-Up Notes:

Circuit Diagrams Electrical Circuits and Short Circuits

Using the Multimeter

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.

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.

Schematic Diagrams

Schematic Diagrams

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

Electric Circuits

Electric Circuits

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.

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.

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!

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

Measuring Voltage and Current

Measuring Voltage and Current

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

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.

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.

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.

Homework

p. 735 #1-5