BellringerA standard household outlet has

a voltage of what?

Electric Circuits

Part I

Ohm’s Law

•Current, voltage, and resistance are related to one another. The relationship among resistance, voltage, and current is summed up in Ohm’s Law.

Ohm’s Law• Ohm’s Law states that the resistance of

most conductors does not depend on the voltage across them.

• Changing the voltage in a circuit changes the current but will not change the resistance.

• Ohm concluded that conductors and most other devices have a constant resistance regardless of the applied voltage.

Ohm’s Law•The equation for Ohm’s Law is:

• The units in the equation are:

Ohms (Ω) = Volts (V) ÷ Amps (A)

CurrentResistance =

Voltageor R=V/I

Ohm’s Law•You can rearrange Ohm’s Law to

find voltage with this equation:

Voltage = Current X Resistance

or

V=IR

Ohm’s Law

If a circuit has a resistance of 30.5 ohms and a current of .05 amps, what is it’s voltage?

1.525 volts

Ohm’s LawThe brake light on an automobile is connected to a 12-volt battery. If the resulting current is 0.40 amps, what is the resistance of the brake light?

30 Ω

Features of a Circuit

•Circuits have devices that are run by electrical energy.

•A circuit has a source of electrical energy.

•Electric circuits are connected by conducting wires.

Features of a Circuit

•Radios, appliances, and light bulbs are examples of electrical devices. All these devices resist the flow of electrical energy. As a result, electrical devices are known as resistors.

Features of a Circuit

•Sources of electrical energy in a circuit include batteries, generators, and electric power plants. When you plug a radio into a wall socket, the source of electrical energy is your local electric plant.

Features of a Circuit

•Conducting wires complete the path of an electric circuit. Wires allow charges to flow from the energy source to the electric device and back to the energy source.

Features of a Circuit

•Often, a switch is placed in an electric circuit. With a switch, you can turn a device on or off by opening or closing the circuit.

Circuit Diagram

Circuit Diagram