Circuits

Reviewing terms

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.

Rtotal = R1 + R2 + R3...Total

resistance(ohms)

Individual resistances

()

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 ElectricityThe 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.The other common unit of power often

seen on electric motors is the horsepower.One horsepower is 746 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.

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 homesGenerators

produce AC current

Application: Wiring in Homes and Buildings

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: