Voltage, Current, and Resistance

Electric charge

• Electric charge, like mass, is also fundamental property of matter.

• Inside atoms found in matter, attraction between positive and negative charges holds the atoms together.

Charge• Virtually all the matter around

you has electric charge because atoms are made of electrons and protons (and neutrons).

• Because ordinary matter has zero net (total) charge, most matter acts as if there is no electric charge at all.

Electric and magnetic forces• Whether two charges attract

or repel depends on whether they have the same or opposite sign.

• A positive charge attracts a negative charge and vice versa.

• Two similar charges repel each other.

Electrical forces

• The unit of charge is the coulomb (C). The name was chosen in honor of

• Charles Augustin de Coulomb (1736-1806), the French physicist who performed the first accurate measurements of the force between charges.

Voltage, Current, and Resistance

What is current?• describes the flow of electric

charges. • the actual measure of how

many charges are flowing through the circuit in a certain amount of time.

• measured in units called amperes.

Electric Circuits

• An electric circuit is a complete path through which electric current travels.

• A good example of a circuit is the one found in an electric toaster.

Electric Circuits

• When drawing a circuit diagram, symbols are used to represent each part of the circuit.

Electric Circuits

• Electrical symbols are quicker and easier to draw than realistic pictures of the components.

Current in a circuit• Current only flows

when there is a complete and unbroken path, or a closed circuit.

• Flipping a switch to the “off” position creates an open circuit by making a break in the wire.

Voltage, Current, and Resistance

What affects current?• The type of wire• The length of the wire• The thickness of wire. • Resistors slow the flow of current

Voltage, Current, and Resistance

What is voltage?• difference in energy level from one

end of the battery (or any other energy source) to the other.

• measured in volts. • The energy difference causes the

charges to move from a higher to a lower voltage in a closed circuit.

• voltage difference supplies the energy to make charges flow in a circuit.

Voltage, Current, and Resistance

What is resistance?• the measure of how easily

charges flow through a circuit.

• measured in units called ohms (abbreviated with the symbol Ω).

Voltage, Current, and Resistance

What affects resistance?• The type of wire• The length of the wire• The thickness of wire. • Resistors slow the flow of current

Resistance

• The total amount of resistance in a circuit determines the amount of current in the circuit for a given voltage.

Voltage, Current, and Resistance

How are voltage, current, and resistance related?• When the voltage (push) increases the current

(flow of charges) will also increase, and when the voltage decreases, the current likewise decreases. These two variables, voltage and current, are said to be directly proportional.

Voltage, Current, and Resistance

How are voltage, current, and resistance related?• When the resistance in an electric circuit

increases, the flow of charges (current) decreases. These two variables, resistance and current, are said to be inversely proportional. When one goes up, the other goes down, and vice versa.

Voltage, Current, and Resistance

How are voltage, current, and resistance related?• The law that relates these three variables is

called Ohm’s Law. The formula is:

Voltage, Current, and Resistance

In a circuit, how many amps of current flow through a resistor such as a 6-ohm light bulb when using four 1.5-volt batteries as an energy supply?

Voltage, Current, and Resistance

1. What is the difference between placing a 1.5-volt battery in a circuit and placing a 9-volt battery in a circuit?

Voltage, Current, and Resistance

2. What could you do to a closed circuit consisting of a battery, a light bulb, and a switch that would increase the amount of current? Explain your answer.

Voltage, Current, and Resistance

3. What could you do to a closed circuit consisting of a battery, a light bulb, and a switch that would decrease the amount of current? Explain your answer.

Voltage, Current, and Resistance

4. Describe one thing that you could do to the wire used in a circuit to decrease the amount of resistance presented by the wire

Voltage, Current, and Resistance

5. In your own words, state the relationship between resistance and current, as well as the relationship between voltage and current.

Voltage, Current, and Resistance

1. How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance of 6 ohms?

Voltage, Current, and Resistance

2. How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance of 12 ohms?

Voltage, Current, and Resistance

3. How much voltage would be necessary to generate 10 amps of current in a circuit that has 5 ohms of resistance?

Voltage, Current, and Resistance

4. How many ohms of resistance must be present in a circuit that has 120 volts and a current of 10 amps?

Voltage, Current, and Resistance