 An electric circuit is a complete, closed path through which electric charges flow.  A circuit always begins and ends in the same place. It ends in the same place. It forms a loop. forms a loop. Electric Circuits

 All electric circuits have: 1.a voltage source 2.a conductor 3. a switch 4. an electrical device Electric Circuits

 An electric device uses electrical energy to do work.  All loads offer some resistance to electric currents and cause the electrical energy to change into another form of energy, such as light, heat, or kinetic energy. Electric Circuits

 Did you know???  Your body is controlled by a large electric circuit. Electrical impulses from your brain control all the muscles and organs in your body.  The food you eat is the energy source for your body’s circuit,  your nerves are the wires,  and your muscles and organs are the loads! loads!

Electric Circuits  Types of circuits  Series circuits  Parallel circuits  Combination circuits  Short circuit

Electric Circuits  A series circuit is a circuit in which all parts are connected in a single loop.  The charges traveling through a series circuit must flow through each part and can only follow one path.

Electric Circuits  All the loads in a series circuit share the same current. Because the current in all the light bulbs is the same, the bulbs glow with the same brightness. If you add more bulbs, the If you add more bulbs, the resistance of the entire circuit resistance of the entire circuit would increase and the would increase and the current would decrease. All current would decrease. All the bulbs would get dimmer. the bulbs would get dimmer.

Electric Circuits  Some series circuits use a load as a switch. For example, the automatic door at the store is operated by a series circuit with a motor that opens the door and a photoelectric “eye” that acts as an on-off switch.

Electric Circuits  For charges to flow in a series circuit, all the loads must be turned on and working.  Charges pass through one load after another, in order, around the circuit.  IF ONE LOAD IS BROKEN OR MISSING, THE OTHER LOADS WOULD NOT WORK.

Electric Circuits  A parallel circuit is a circuit in which different loads are located on separate branches. Because there are separate branches, the charges travel through more than one path.

Electric Circuits  The loads in a parallel circuit do NOT have the same current in them.  Instead, each load in a parallel circuit uses the same voltage. The full voltage of the battery is connected to each bulb, so each bulb glows at full brightness.

Electric Circuits  You can connect loads that require different currents to the same parallel circuit. For example, you can connect a For example, you can connect a hairdryer (that requires a high hairdryer (that requires a high current) to the same circuit as current) to the same circuit as a lamp (which requires less current.) a lamp (which requires less current.)

Electric Circuits  Broken wires or water can cause short circuits. A short circuit occurs when charges bypass the loads in the circuit.  When the loads are bypassed, the resistance of the circuit drops and the current in the circuit increases.  If the current increases too much, it can produce enough thermal energy to start a fire.

Electric Circuits NEVER connect a battery only to itself. Short circuits start dangerous fires every day!

Electric Circuits  Circuit Safety: A fuse contains a thin metal strip that the charges flow through. If the current is too high, the metal in the fuse warms up and melts. A break in the circuit is produced and the current stops flowing.

Electric Circuits  Circuit Safety: A circuit breaker is a switch that automatically opens if the current in the circuit is too high.  If the current is too high, a strip of metal in the circuit breaker warms up and bends away from the wires in the circuit.

Electric Circuits  A device that acts like a miniature circuit breakers is a ground fault circuit interrupter (GFCI). It compares the current in one side of an outlet with the current in the other side.  If there is a difference, it opens the circuit and you must push the reset button to close it again.