Electricity: The Mouse and Cheese Analogy All matter is made up of positive charges and negative charges. The positives have mass and are not usually free to move. The negatives have no mass and are free to move through some materials (conductors).

Mouse and Cheese Analogy Negative charges are attracted to positive charges the same way mice are attracted to cheese. Any time there is a natural attraction between two things we can use it to make the objects do work. The negative charges (mice) will gladly do work in order to get to the positive charges (cheese).

Electric Current Continuous flow of electric charge. SI unit of electric current is the AMPERE (A) or amp. 1 amp = 1 coulomb per second. Two types of electric current: Direct Current (DC) Alternating Current (AC)

Mouse and Cheese Analogy Current: The number of charges (mice) passing a point per second. The rate of flow of charges.

Direct Current DC Charges flow in one direction. Most battery operated items use DC. http://www.geocities.com/capecanaveral/hall/6645/electmag/electricmotor.htm

Alternating Current Flow of electric charge that regularly reverses its direction. Most electric current at home and school. Dotted lines are from AC

Conductor and Insulator Electrical Conductor Material through which charge can flow easily. Copper and Silver Electrical Insulator Coating around a wire that controls the current and keeps it where its needed. Wood, plastic, air Rubber Insulating Material (plastic) Conducting Wire (copper)

Superconductor Material that has almost zero resistance when cooled to low temperatures. Best superconductors must be cooled to 138K.

Resistance Opposition to the flow of charges in a material. SI unit of resistance is ohm (Ω). Four factors affect the resistance in a wire: Material type Thickness Length Temperature

Mouse and Cheese Analogy Resistance: The opposition to the flow of charge. Any appliance that asks the charge (mouse) to do work will slow it down.

Voltage The difference of electrical potential between two points of an electrical circuit. Also called the potential difference. SI unit for voltage is a VOLT One volt = one joule per coulomb

Mouse and Cheese Analogy Voltage: The amount of work that each charge (mouse) will do as it goes through the circuit. Can also be thought of as the amount of push on the charges or how hungry the mice are.

Voltage Sources Three common voltage sources: Battery Solar Cell Generator

Battery Device that converts chemical energy to electrical energy

Ohm’s Law Georg Ohm (1789-1854) Ohm’s Law: Found a relationship between voltage, current, and resistance. Ohm’s Law: The voltage (V) in a circuit equals the product of the current (I) and the resistance (R). V = I x R I = V R = V R I

Chapter 20.3 Electrical Circuits

Circuit Diagrams Use symbols to represent parts of a circuit. Include: Sources of electrical energy Devices that are run by electrical energy

Types of Circuits

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. The bulbs in a circuit are a source of resistance. The more bulbs, the more resistance.

Parallel Circuit Charge has TWO OR MORE paths through which the charge can flow. If one element stops functioning, the rest of the elements can still operate.