Electric Circuits Prentice Hall: Electricity and Magnetism Chapter 2, Section 4 Mrs. Brunner Science Visit for review

I. Ohm’s Law A. George Ohm (1800) – discovered relationship between current, voltage, and resistance B. Ohm’s Results 1. Changing the voltage in a circuit changes the current, but 1. Changing the voltage in a circuit changes the current, but will not change the resistance will not change the resistance C. Calculating Ohm’s Law 1. puts the relationship between current, voltage, and resistance 1. puts the relationship between current, voltage, and resistance into numbers into numbers 2. resistance is equal to the voltage divided by the current 2. resistance is equal to the voltage divided by the current resistance = voltage resistance = voltage current current 3. another way to write the equation is 3. another way to write the equation is voltage = current x resistance voltage = current x resistance D. Practice with problems in the book! D. Practice with problems in the book!

II. Features of a Circuit A. Devices that run by electric energy B. Has a source of electrical energy C. Circuits are connected by wires III. Series Circuits  A. type of circuit that has only path for the electricity to travel on  B. if one device on the circuit goes out, all the devices go out – this is a problem  C. the more light bulbs you add to a series circuit, the dimmer they become…Why? 1. bulb acts as a resistor1. bulb acts as a resistor 2. when resistance increases, current decreases2. when resistance increases, current decreases

 IV. Parallel Circuits 1. type of circuit where there are several paths for the electricity to travel on 1. type of circuit where there are several paths for the electricity to travel on 2. If one device goes out, other devices on the circuit do NOT go out 2. If one device goes out, other devices on the circuit do NOT go out 3. When you add a ‘branch’ to a circuit, the overall resistance decreased 3. When you add a ‘branch’ to a circuit, the overall resistance decreased 4. If resistance decreases than the current will increase so any light bulbs on the circuit will not get dimmer 4. If resistance decreases than the current will increase so any light bulbs on the circuit will not get dimmer  V. Ammeter – device that measures current  VI. Voltmeter – device that measures voltage or potential energy difference, most circuits in your house can carry 120 volts