Electric Current and Ohms Law

Electric Current

• The continuous flow of electric charge– The two types of current are direct current

(DC) and alternating current (AC)

Voltage

• Potential difference: the difference in electrical – Measured in Volts (v)

• In order for charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy

Ohm’s Law

• The Voltage in a circuit equals the product of the current (I) and resistance (R)– V=I x R or I = V

R

I- amperes

R - ohms

Practice Problem

What is the voltage if the resistance is 3 ohms and the current is 3 amps?

More Practice Problems

• What is the current if there is 10 volts, and 4 ohms of resistance?

• What is the resistance if there is 12 volts and 6 amps of current?

• What is the voltage if there is 4.5 amps and 6 ohms of resistance?

• Increasing the voltage increases the current. Keeping the same voltage and increasing the resistance decreases the current.

Electric Circuit

• A complete path through which charge can flow.

• Circuit diagrams se symbols to represent parts of a circuit, including a source of energy and devices that are run by electrical energy. – Switches can show if the circuit is open or

closed

Series Circuits

• Charge has only one path through which it can flow

• If one element stops functioning in a series circuit, none of the elements can operate.

• Example: christmas lights

Parallel Circuit

• An electrical circuit with two or more paths through which charges can flow

• If one element stops functioning in a parallel circuit, the rest of the elements still can operate.

• Ex. Light bulbs in your house

Catalyst

• If I have a battery that can output 120 volts and a resistance of 30 ohms, what is the current that is able to flow through the circuit?

Electric Power

• The rate at which electrical energy is converted to another form of energy– Measured in Joule/second or Watt

• P(watts) = I (amps) x V (volts)

Practice Problems

• An electric oven is connected to a 240-volt line, and it uses 34 amps of current. What is the power used by the oven?

More Practice Problems

• Every Time you use a 1875- watt hair dryer, you send through a current of 35 amps. What is the voltage used by the hair dryer?

• If you are using 250 volts and a power of 2500 watts, what is the current that runs through the circuit?

More practice problems

• 1-3 on page 611

• 7-8 on page 613

Online practice

• http://www.wisc-online.com/objects/index_tj.asp?objID=dce11904

• http://www.allaboutcircuits.com/worksheets/ewp.html