Bellringer
A 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:
Voltage
Resistance =
Current
or R=V/I
• The units in the equation are:
• Ohms (Ω) = Volts (V) ÷ Amps (A)
Ohm’s Law
•You can rearrange Ohm’s Law to find
voltage with this equation:
•Voltage
•or
•V=IR
= Current X Resistance
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 Law
• The 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