Circuits

Reviewing terms

The Electric Force and the Electric Field The force between charged objects is an electric force. An electric field is the region around a charged object in which an electric force is exerted on another charged object.

Parts of a Circuit Forming a Loop An electric circuit is a complete, closed path through which electric charges flow. All circuits need three basic parts: an energy source, wires, and a load.

Law of Electric Charge

Parts of a circuit

Series and Parallel Circuits Key Question: How do series and parallel circuits work?

Series and Parallel Circuits In series circuits, current can only take one path. The amount of current is the same at all points in a series circuit.

Adding resistances in series Each resistance in a series circuit adds to the total resistance of the circuit.

Total resistance in a series circuit Light bulbs, resistors, motors, and heaters usually have much greater resistance than wires and batteries.

Voltage Voltage is the rate at which energy is drawn from a source that produces a flow of electricity in a circuit; expressed in volts

Voltage in a series circuit Each separate resistance creates a voltage drop as the current passes through. As current flows along a series circuit, each type of resistor transforms some of the electrical energy into another form of energy

Series and Parallel Circuits In parallel circuits the current can take more than one path. Because there are multiple branches, the current is not the same at all points in a parallel circuit.

Series and Parallel Circuits When analyzing a parallel circuit, remember that the current always has to go somewhere.

Voltage and current in a parallel circuit In a parallel circuit the voltage is the same across each branch because each branch has a low resistance path back to the battery. The amount of current in each branch in a parallel circuit is not necessarily the same. The resistance in each branch determines the current in that branch.

Advantages of parallel circuits Parallel circuits have two big advantages over series circuits: 1. Each device in the circuit sees the full battery voltage. 2. Each device in the circuit may be turned off independently without stopping the current flowing to other devices in the circuit.

Short circuit A short circuit is a parallel path in a circuit with zero or very low resistance. Short circuits can be made accidentally by connecting a wire between two other wires at different voltages. Short circuits are dangerous because they can draw huge amounts of current.

Resistance in parallel circuits Adding resistance in parallel provides another path for current, and more current flows. When more current flows for the same voltage, the total resistance of the circuit decreases. This happens because every new path in a parallel circuit allows more current to flow for the same voltage.

Electric Power, AC, and DC Electricity Key Question: How much does electricity cost and what do you pay for?

Electric Power, AC, and DC Electricity The watt (W) is a unit of power. Power is the rate at which energy moves or is used. Since energy is measured in joules, power is measured in joules per second. One joule per second is equal to one watt.

Power in electric circuits One watt is a pretty small amount of power. In everyday use, larger units are more convenient to use. A kilowatt (kW) is equal to 1,000 watts.

Paying for electricity Electric companies charge for the number of kilowatt-hours used during a set period of time, often a month. One kilowatt-hour (kWh) means that a kilowatt of power has been used for one hour. Since power multiplied by time is energy, a kilowatt-hour is a unit of energy.

Electric Current AC and DC There are two kinds of electric current—direct current (DC) and alternating current (AC).

Alternating and direct current DC—Direct Current—produced by solar cells and chemical cells (batteries) Current only flows in one direction. One end of the battery is positive and the other end is negative.

Alternating and direct current AC—Alternating Current Current flows back and forth (alternates) Found in homes Generators produce AC current

Application: Wiring in Homes and Buildings

Toll Road—Circuit Analogy

Toll Booth Explanation Adding toll booths in series increases resistance and slows the current flow. Adding toll booths in parallel lowers resistance and increases the current flow.

Batteries in Series & Parallel:

Charge It

Moving Charges An electrical conductor is a material in which charges can move easily. An electrical insulator is a material in which charges cannot move easily.

Electric changes Static electricity is the electric charge at rest on an object. The loss of static electricity as charges move off an object is called electric discharge. One of the most dramatic examples of electric discharge is lightning. The next slide shows how lightning is formed.

Study Guide Answers