Series and Parallel Circuits Lesson 9 December 12th , 2011 Series and Parallel Circuits

Review

Current Current is the rate of charge flow and is given the symbol I. Current is the total amount of charge moving past a particular point in a conductor divided by the time taken.

Measurement of current An Ammeter (a current measuring device) must be wired so that all current flows through it. The ammeter must be an excellent conductor so that no energy is lost due to its addition to the circuit.

Current Charge Time

Series and Parallel Circuits

Series Circuits An electric circuit in which the components are arranged one after another in series. A series circuit has only one path along which electrons can flow. If that pathway is interrupted, the whole circuit cannot function.

Series Circuits The amount of current is the same in all parts of a series circuit. If more resistors are added, it will increase the total resistance of the circuit. This decreases the current.

Series Circuits Example: Adding an extra bulb to a series string of lights makes all the bulbs dimmer. Electrons use up all their potential difference going around a series circuit no matter how many loads are in the circuit. Each load will use part of the total potential difference, depending on how much it resists the flow of electrons.

Parallel Circuits A parallel circuit is an electric circuit in which the parts are arranged so that electrons can flow along more than one path. The points where a circuit divides into different paths or where paths combine are called junction points An interruption or break in one pathway does not affect the other pathways in the circuit.

Parallel Circuits Similarly, adding a new pathway with more resistors does not affect the resistance in any of the other pathways. Adding extra resistors in parallel decreases the total resistance of the circuit.

Parallel Circuits Each electron has the same amount of energy, and electrons must expend all their energy on the path they are on. This is why the potential difference across parallel resistors will always be the same, even though the resistors themselves are of different values

Loads connected in parallel circuits have different currents

Kirchhoff’s current law the total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.

In the diagram to blow, three branches are coming together at one junction point and two branches leave. I1 + I2 + I3 = I4 + I5

Current According to Kirchhoff’s current law, this series circuit has no real junction point, so it has only one path to follow. Therefore,

IT = I1 = I2 = I3 = IT = 10 A R2 R1 I3 10.0 A 30 V V2 100v

Current There are 4 junction points in this diagram. One at the top and bottom of each branch, to resistors 1 and 2. The sum of the current entering the junctions must equal the sum exiting. 9.0 A I3 3.0 A R3 R2 R1 30V V2

IT = I1 + I2 + I3 = 9 A I3 = IT – I1 – I2 = 9 A – 3 A – 3A = 3A

Summary of Current, potential difference, and resistance in series and parallel circuits. Series circuit Each load uses a portion of the total potential differences supplies by the battery VT = V1 + V2 + V3

Summary of Current, potential difference, and resistance in series and parallel circuits. Each load uses all the potential difference supplied by the battery. VT = V1 = V2 = V3

Summary of Current, potential difference, and resistance in series and parallel circuits. Series circuit The current is the same throughout a series circuit Itotal = I1 = I2 = I3

Current in a series circuit example IT = I1 = I2 = I3 I3 = 10 A R2 R1 I3 10.0 A 30 V V2 100v

Summary of Current, potential difference, and resistance in series and parallel circuits. The current divides into different paths. A pathway with less resistance will have a greater current Itotal = I1 + I2 + I3

Current in a parallel circuit example IT = I1 + I2 + I3 = 9 A I3 = IT – I1 – I2 = 9 A – 3 A – 3A = 3A 9.0 A I3 3.0 A R3 R2 R1 30V V2

Summary of Current, potential difference, and resistance in series and parallel circuits. Series circuit The current decreases when more resistors are added RT = R1 + R2 + R3

Summary of Current, potential difference, and resistance in series and parallel circuits. Adding resistors in parallel decreases the total resistance of the circuit.

Two Types of Circuits Combined Series circuits and parallel circuits make up the circuits in your home and school.

Two Types of Circuits Combined Some circuits are combinations of series circuits and parallel circuits. These combinations help prevent problems such as the all the lights in the house going out because one bulb burnt out.

It is also an important safety feature in a combination circuit to have some switches wired in series, because it is sometimes necessary to turn off the electricity in part or all of a home

Current Lab Work in groups of 4 Follow directions Everyone must hand in their own work.