Circuit A complete path of conductors from the negative terminal of the voltage source back to the positive terminal of the voltage source. Two main types of circuits: Series Parallel What’s wrong in this picture???

What is a circuit? Would the light bulb still light up if the filament were broken? No! The electrons must have a complete circuit to flow through. A circuit is any path along which electrons can flow. For the continuous flow of electrons, there must be a complete circuit with no gaps

Circuits Series One path. All current flows through all parts of the circuit. “All or nothing” If there is a break in the circuit, open circuit, no current will flow. Parallel More than one path. Current splits and travels through different paths. “Selective” If there is a break in one branch of the circuit, current can still flow through other branches. What’s wrong in this picture???

Circuit Elements We have already talked about some properties of an electrical circuit… Current, which is the flow of electrons. Resistance, which is the slowing of electrons. Voltage, which produces the flow of electrons. These properties have different parts of a circuit, or circuit elements.

Series Circuits When items are connected in series, they provide one single path for the current to flow through For example, when the current travels out of the wall, through the filament, and back into the wall, the light bulb has been connected in series

Series Circuits There are four important characteristics of a 1. Current has a single pathway through the circuit, so current through each device is the same. 2. Current is resisted by the first device, then the second, then the third and so on, so the total resistance is the sum of the individual resistances

3. The current in the circuit is equal to the voltage from the voltage source divided by the total resistance in the circuit (Ohm’s Law, duh!) 4. Ohm’s Law applies separately to each device, so the voltage drops across each device, according to its resistance

Series Circuits Series circuits have some pretty obvious disadvantages If several light bulbs are connected in series, and one goes out, what happens to the circuit? This idea may be familiar to you through some traumatizing Christmas-tree decorating experience.

Parallel Circuit When items are connected in parallel, they form separate branches, any one of which the electrons can flow through. In a parallel circuit, all of the electrons DO NOT flow through all of the circuit elements

Parallel Circuit There are four important characteristics of parallel circuits: 1. Each device connects the same two points in a circuit, so the voltage is the same across each device. 2. The total current in the circuit splits up among the different branches (think of the electrons getting to chose which branch they go down), so the current is different across each branch. More current passes through the branches with lower resistance (Ohm’sLaw)

Parallel Circuit The total current in the circuit equals the sum of the currents in its parallel branches. 4. As the number of parallel branches increases,the total resistance decreases. Think of checking out at the grocery store. A certain number of people need to check out (like electrons in a circuit). As more check-out lanes open, the people can move through more quickly. Thus as the number of lanes increases, the“resistance” decrease.

Review and Compare Series Parallel All electrons pass through single path Voltage drops different across each device Current is the same through each device Parallel Electrons pass through one of many paths Voltage is the same across each device Current is different through each device

Current through a conductor is proportional to the applied voltage Ohm’s Law Current through a conductor is proportional to the applied voltage Conductor is also known as a resistor An ideal conductor is a material whose resistance does not change with temperature V = Voltage (Volts = V) I = Current (Amperes = A) R = Resistance (Ohms = Ω)

Current and Voltage Defined Current: (the current in electrical circuits) Flow of current from positive terminal to the negative terminal. - has units of Amperes (A) and is measured using ammeters. Voltage: Energy required to move a charge from one point to another. - has units of Volts (V) and is measured using voltmeters. Think of voltage as what pushes the electrons along in the circuit, and current as a group of electrons that are constantly trying to reach a state of equilibrium.

Ohm’s Law continued

Ohm’s Law continued The total resistance of a circuit is dependant on the number of resistors in the circuit and their configuration Series Circuit Parallel Circuit

Circuits Series Each resistor added decreases the voltage. (Loads share the current.) RT = R1 + R2 +R3… As resistors are added, total resistance increases. Parallel Each resistor gets full voltage. (Each load draws own current.) 1/RT = 1/R1 + 1/R2… As resistors are added, total resistance decreases.

Fuses & Circuit Breakers Limit the current that runs through wires in your house These wires have some resistance Energy loss by I2R converts to heat Hot wires can start a fire Limit the current with a fuse or circuit breaker