Physics Circuit Types

Circuits Need a source of energy, a pathway for electrons, and something that uses energy. Ex) Sources: Battery, 120 V plug, AC generator, DC generator Pathway: Wires (copper or silver) Loads (use energy): light bulbs, motors, heater, MP3 player A switch is used to control a circuit.

Switches/fuses An open switch interrupts the path and causes an open circuit. A closed switch allows electrons to flow thus turning the circuit on. (Light switch at home, power button on Blu-ray player) A fuse is also used to stop too much current from flowing through a circuit which could damage loads. A fuse creates an open circuit when it melts and is part of the circuit. A circuit breaker at home works similarly, except you can re-use it.

Circuit Symbols + – 1.5 V Cell DC Generator AC Generator Open Switch Closed Switch + – DC AC

Circuit Symbols Resistor Lamp Fuse Motor M

Cells Symbol for one cell consists of a short line (negative terminal) and a long line (positive terminal). Adding cells together in series increases the voltage. Electrons always flow away from the negative terminal and around a circuit to the positive one. Note: Conventional current is used by engineers or electricians and is opposite to electron flow (current). (Conventional current flows into a negative terminal). – +

Cells in series Cells connected in series are added together to give total voltage. (one cell = 1.5 V) Two cells in series add to 3.0 V

Cells in parallel Cells connected in parallel have the same voltage applied on each path. Lasts longer, but delivers same voltage. Increases charge, but not potential. 1.5 V

Series Circuit layout In a circuit, if there is one path: it is a series circuit.

Series circuits The current is the same through the loads. All loads are in one path, so one switch is needed to control the whole circuit. Unscrewing a light bulb will create an open circuit. Voltage is divided up among the loads based on the resistance. A higher resistance load will use more voltage. All the voltage gains are equal to the voltage losses for the one path.

Parallel circuit layout A circuit with more than one path is a parallel circuit. Combinations also occur.

Parallel circuits Current passes through separate circuits to each load. Each separate circuit is called a branch circuit. Unscrewing a light bulb will stop current flow in that path only. The current splits up to each path based on resistances of each path. A path with lower resistance will have more current.

Parallel circuits All the current that leaves a battery recombines again back at the battery. Therefore, the currents for each branch add up to the total current. Along each path, the voltage is the same. (All the voltage gains are equal to the voltage losses for the one path.)

Circuit Diagrams Draw a circuit with a DC Power source, two resistors in parallel, an ammeter measures total current and a voltmeter measures the voltage drop across one resistor.

Circuit Diagrams Draw a circuit diagram with 2 bulbs in series, a switch that controls the circuit, a fuse and 3 cells connected in series.

Circuit Diagrams Draw a circuit with 6.0 V in cells, controlled by a switch, in series with a light bulb and a resistor. What is the voltage at the light bulb and resistor if they have the same resistance? If 0.2A of current flows in this circuit, what current flows through the bulb and the resistor? Determine the resistance for the two loads using Ohm’s Law.