20.1 Electric Circuits pp 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, often called circuit diagrams, are used to represent the design of electrical circuits.  Like force diagrams represent forces.

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

 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