Electricity

• 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.

Positive and Negative Charge

• Some materials hold onto their electrons more tightly or loosely.

Transferring Charge

• When you walk on the carpet, electrons are transferred from the carpet to the soles of your shoes.

• 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.

Transferring Charge

Conservation of Charge

• According to the law of conservation of charge, charge can be transferred from object to object, but it cannot be created or destroyed.

• Whenever an object becomes charged, electric charges have moved from one place to another.

Behavior of Charges

Opposite charges attract

Like charges repel

• Unlike charges attract each other, and like charges repel each other.

• The force between any two objects that are electrically charged decreases as the objects get farther apart.

Electric Fields

• Any charge that is placed in an electric field will be pushed or pulled by the field.

• An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled.

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.

• A material in which electrons are able to move easily is a conductor.

• A material in which electrons are not able to move easily is an insulator.

Conductors and Insulators

*Metals

•Electrolytes

•Human body

•Earth’s Crust

•Plastics

•Styrofoam

•Wood

•Rubber

•Paper

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.

• 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.

Charging Objects

Induction of an Electric Field (Balloon and Board Drawing)

Series Circuit• The current only has 1 loop to flow

through.

• Used in 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

• 1 useful device that prevents electric circuits from overheating.

• Fuses are small pieces of metal that melt if the current becomes too high. The 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 the current and voltage used in an appliance.

• It is measured in Watts or Kilowatts.

• P = IV

• Power = Current (amps) x voltage (volts)

• Ohm’s Law: The 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.

Current and 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.

Voltage Difference

3 Variables in a Circuit1. 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.

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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