Electric CircuitsElectric CircuitsPrentice Hall: Electricity and MagnetismPrentice Hall: Electricity and Magnetism

Chapter 2, Section 4Chapter 2, Section 4

Mrs. BrunnerMrs. Brunner

ScienceScienceVisit Visit www.phschool.comwww.phschool.com for review for review

I. Ohm’s LawI. Ohm’s Law

A. George Ohm (1800) – discovered relationship A. George Ohm (1800) – discovered relationship between current, voltage, and resistancebetween current, voltage, and resistance

B. Ohm’s Results B. Ohm’s Results

1. Changing the voltage in a circuit changes the 1. Changing the voltage in a circuit changes the current, but current, but

will not change the resistance will not change the resistance

C. Calculating Ohm’s LawC. Calculating Ohm’s Law

1. puts the relationship between current, 1. puts the relationship between current, voltage, and resistancevoltage, and resistance

into numbersinto numbers

2. resistance is equal to the voltage divided 2. resistance is equal to the voltage divided by the currentby the current

resistance = resistance = voltagevoltage

currentcurrent

3. another way to write the equation is3. another way to write the equation is

voltage = current x resistancevoltage = current x resistance

D. Practice with problems in the book!D. Practice with problems in the book!

II. Features of a CircuitII. Features of a Circuit

A. Devices that run by electric energyA. Devices that run by electric energy

B. Has a source of electrical energyB. Has a source of electrical energy

C. Circuits are connected by wires C. Circuits are connected by wires

III. Series CircuitsIII. Series Circuits

A. type of circuit that has only path for the A. type of circuit that has only path for the electricity to travel on electricity to travel on

B. if one device on the circuit goes out, all the B. if one device on the circuit goes out, all the devices go out – this is a problemdevices go out – this is a problem

C. the more light bulbs you add to a series circuit, C. the more light bulbs you add to a series circuit, the dimmer they become…Why?the dimmer they become…Why?• 1. bulb acts as a resistor 1. bulb acts as a resistor

• 2. when resistance increases, current decreases2. when resistance increases, current decreases

IV. Parallel CircuitsIV. Parallel Circuits 1. type of circuit where there are several paths for the 1. type of circuit where there are several paths for the

electricity to travel onelectricity to travel on

2. If one device goes out, other devices on the circuit do 2. If one device goes out, other devices on the circuit do NOT go outNOT go out

3. When you add a ‘branch’ to a circuit, the overall 3. When you add a ‘branch’ to a circuit, the overall resistance decreasedresistance decreased

4. If resistance decreases than the current will increase 4. If resistance decreases than the current will increase so any light bulbs on the circuit will not get dimmerso any light bulbs on the circuit will not get dimmer

V. Ammeter – device that measures currentV. Ammeter – device that measures current

VI. Voltmeter – device that measures voltage or VI. Voltmeter – device that measures voltage or potential energy difference, most circuits in your potential energy difference, most circuits in your house can carry 120 voltshouse can carry 120 volts