Upload
winfred-parsons
View
222
Download
1
Tags:
Embed Size (px)
Citation preview
• 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
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.
----- ----- ----- ----- ----- -----
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.