Electricity

Positive and Negative Charge 2 Electric Charges: Proton = Positive charge Electron = Negative Charge The amount of positive charge on a proton equals the amount of negative charge on an electron.

Transferring Charge Some materials hold onto their electrons more tightly or loosely. When you walk on the carpet, electrons are transferred from the carpet to the soles of your shoes.

Transferring Charge The soles of your shoes have an excess of electrons and become negatively charged. The carpet has lost electrons and has an excess of positive charge. The accumulation of excess electric charge on an object is called static electricity.

Conservation of Charge Law of conservation of charge, charge can be transferred from object to object, but cannot be created or destroyed. Whenever an object becomes charged, electric charges have moved from one place to another.

Opposite charges attract Behavior of Charges Unlike charges attract, like charges repel. Opposite charges attract Like charges repel Force between any 2 objects that are electrically charged decreases as the objects get farther apart.

Electric Fields An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled. Any charge placed in an electric field will be pushed or pulled by the field.

Conductors and Insulators If you reach for a metal doorknob after walking across a carpet, you might see a spark. The spark is caused by electrons moving from your hand to the doorknob.

Conductors and Insulators A material in which electrons are not able to move easily is an insulator. A material in which electrons are able to move easily is a conductor. Plastics Styrofoam Wood Rubber Paper Metals Electrolytes Human body Earth’s Crust

Charging Objects Rubbing two materials together can result in a transfer of electrons. Then one material is left with a positive charge and the other with an equal amount of negative charge. The process of transferring charge by touching or rubbing is called charging by contact.

Charging Objects Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction.

Series Circuit The current only has 1 loop to flow through. Used in older holiday lights and flashlights Disadvantage: one break in the circuit disrupts entire loop.

Parallel Circuits Contain 2 or more pathways for current to move through. Ex: Homes, cars and airplanes are wired with parallel circuits. Advantages: Some branches can be turned off without affecting the others.

Fuses Useful device that prevents electric circuits from overheating. Fuses - small pieces of metal that melt if the current is too high. Melting causes a break in the circuit and stops the flow of current. Fuses must be replaced once “blown”

Circuit Breaker Device used to prevent electric circuits from overheating. Contains a piece of metal that heats up and expands when the current is too large. They can be reset by switching back to “on” position

Electric Power Depends on current and voltage used in an appliance. Measured in Watts or Kilowatts P = IV Power = Current (amps) x voltage (volts)

Current and Voltage Difference Ohm’s Law: relationship between voltage, resistance, and current. Electrons move through conductors from an area of high voltage to an area of low voltage. EX: from a battery to a machine. Batteries usually provide the voltage difference, which causes electrons to move.

Voltage Difference In some ways, the electric force that causes charges to flow is similar to the force acting on the water in a pipe. Water flows from higher pressure to lower pressure.

Voltage Difference A voltage difference is related to the force that causes electric charges to flow. Voltage difference is measured in volts.

3 Variables in a Circuit 1. Voltage: the measure of volts or the potential difference. **Electric charges have potential energy that depends on the position in electric fields. Just as a ball rolls down a hill, a negative charge will move away from another negative charge. (Repulsive forces) This is known as Potential Difference. ----- ----- ----- ----- ----- -----

3 Variables in a Circuit 2. Electrical Current: is the flow of charges through a wire. (I)

3 Variables in a Circuit 3. Resistance: The tendency for a material to oppose/resist the flow of electrons. Resistance is measured in ohms ().

2 Ways to change resistance 1. Materials: can have hi or low resistance Ex: copper has low resistance and can carry electrons quickly. This wire doesn’t lose much energy or heat. Ex: Tungsten (W) has a high resistance and doesn’t let electrons flow fast. Therefore it heats up quickly. It loses heat and glows. Used in light bulbs

2 Ways to change resistance 2. Thickness of wire: Thick wire allows electrons to move fast and has low resistance. Thin wire doesn’t allow electrons to move fast and has high resistance.

Ohm’s Law Ohm’s Law states that I = V/R V =IR R = V/I