Electric Circuits Chapter 35

A Battery and a Bulb In order to light a light bulb, you must have a complete circuit Circuit – any complete path along which charge can flow Electrons flow from the negative part to the positive part of the battery through the wire and whatever else is in its path The electrons do not “squash up” and concentrate in certain places; they flow continuously around a circuit

A Battery and a Bulb

Electric Circuits Any path along which electrons can flow is a circuit For a continuous flow of electrons, there must be a complete circuit with no gaps A gap is usually provided by an electric switch that can be opened or closed to either cut off or allow electron flow In Series – applied to portions of an electric circuit that are connected in a row so that the current that goes through one must go through all of them In Parallel – applied to portions of an electric circuit that are connected at two points and provide alternative paths for the current between those two points

Electric Circuits

Series Circuits Series Circuit – devices are arranged so that charge flows through each in turn; if one part should stop current, it will stop throughout Series circuits follow 5 important rules: 1.A break anywhere in the path stops the electron flow in the entire circuit 2.The total resistance is equal to the sum of individual resistances along the current path 3.The current is equal to the voltage divided by the total resistance 4.The voltage drop across each device is proportional to its resistance 5.The sum of voltage drops across the resistance of the individual devices is equal to the total voltage

Series Circuits

Parallel Circuits Parallel Circuit – devices are connected to the same two points of the circuit, so that any single device completes the circuit independently of the others Parallel circuits follow 4 important rules: 1.Each device connects the same two points of the circuit; the voltage is the same across each device 2.The amount of current in each branch is inversely proportional to the resistance of the branch 3.The total current is equal to the sum of the currents in the branches 4.As the number of parallel branches is increased, the overall resistance of the circuit is decreased

Parallel Circuits

Schematic Diagrams Schematic Diagram – describes an electric circuit, using special symbols to represent different devices in the circuit Resistance is shown as a zigzag line A battery is represented with a set of short and long parallel lines (positive = long and negative = short)

Schematic Diagrams

Combining Resistors in a Compound Circuit 1 / R eq = 1 / R / R / R

Combining Resistors in a Compound Circuit R eq = R 1 + R 2 + R

What’s the Total Resistance? 10Ω

Parallel Circuits and Overloading Lines carrying an unsafe amount of current are overloaded To prevent overloading, fuses or circuit breakers are inserted in lines that provide power Excessive current will “blow out” the fuse or “trip” the circuit breaker, stopping the current A short circuit is often caused by faulty wire insulation

Parallel Circuits and Overloading

Homework Read Chapter 35 (pg ) Do #16-33 ( ) Do #1-8 in Appendix F (pg. 690)