Electric Circuits

Electric circuit: a complete path from the positive terminal to the negative terminal.

Any path along which electrons can flow is a circuit.

A gap is usually provided by an electric switch that can open or closes the circuit allowing the electrons to flow or be cut off.

Many circuits have more than one device that receives electrical energy. They can connect one of two ways……

In series – they form a single pathway for the electrons to flow between terminals of the battery, generator or wall socket.

Series Circuits Current through one bulb travels through the others.

Current has but a single pathway through the circuit. This current is resisted by the resistance of the first device, the resistance of the second device, etc……. Total resistance to the current is the sum of the individual resistances along the path.

So for series circuits, as more resistors are added the overall current within the circuit decreases. This decrease in current is consistent with the conclusion that the overall resistance increases.

The current in the circuit is numerically equal to the voltage supplied by the source divided by the total resistance of the circuit. This is Ohm’s law.

In Parallel – they form branches, each of which is a separate path for the flow of electrons.

Parallel Circuits Voltage same across each bulb. Current same because resistance of each bulb is the same

Each device connects to the same two points of the circuit. The voltage drop is therefore the same across each device

Total current is divided among the parallel branches. Current passes more easily into devices of low resistance, so the amount of current in each branch is inversely proportional to the resistance in each branch. (Ohm’s law applies individually to each branch)

The total current in the circuit equals the sum of the currents in the parallel branches

As the number of branches is increased, Overall resistance is lowered. This means the overall resistance of the circuit is less than the resistance of any one of the branches.

How to find resistance in a series and parallel circuit.

Series: add all the resistance together. 1 Ohm + 1 Ohm = 2 Ohms

In series, the total resistance is always larger than any individual resistance.

Parallel: Use the formula

In parallel circuits, the total resistance is always smaller than any individual resistance.

a. Two 3- resistors placed in series would provide a resistance which is equivalent to one _____- resistor. b. Three 3- resistors placed in series would provide a resistance which is equivalent to one _____- resistor. c. Three 5- resistors placed in series would provide a resistance which is equivalent to one _____- resistor.

d. Three resistors with resistance values of 2-, 4-, and 6- are placed in series. These would provide a resistance which is equivalent to one _____- resistor. e. Three resistors with resistance values of 5-, 6-, and 7- are placed in series. These would provide a resistance which is equivalent to one _____- resistor.

2. As the number of resistors in a series circuit increases, the overall resistance __________ (increases, decreases, remains the same) and the current in the circuit __________ (increases, decreases, remains the same).

As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit ____________ (increases, decreases) and the total current of the circuit ____________ (increases, decreases).