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Electricity

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Static Electricity Static electricity is the buildup of excess electric charge on an object

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Why do you get shocked? Walking across the carpet moves electrons from atoms in the carpet to your shoes, the carpet is no longer neutral and you have a negative charge stored on your body.

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Conservation of Charge Charge can be transferred from object to object, but it cannot be created or destroyed

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Charges Opposite charges attract, like charges repel

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Electric Field and Force An electric field is surrounds all electric charges and exerts a force on other electric charges

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Materials A conductor is a material throught which electrons pass easily An insulator is a material that electrons do not move easily through

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Induction Induction is the charging of an object over a distance

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Electroscope An electroscope is a device to measure electric charge

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Lightning Lightning is a large discharge of static electricity Is caused by friction from the movement of rain drops in clouds. It builds areas of positve and negative charges Lightning can contain 100 million volts and can be hotter than the sun

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Grounding – providing a path to the Earth for a charge to go through

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Potential Difference Is the differnce in electric potential energy between two points It is measured in volts Electrons flow from high potential energy to low potential energy.

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Electric Current

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What is electric current? Electric current is the flow of electrons through a conductor It is measured in amperes (amps) The amount of current depends on the number of electrons passing a given point in a given time

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Circuit A circuit is a closed path through which current can flow If there is no circuit, electricity will not flow

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Think of electricity is like water in pipes Why does water flow through a hose? It goes from high pressure to low pressure Electricity goes from high potential to low potential A battery is like a pump

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Once there is no longer a pressure difference, water stops flowing Once there is no longer a difference in electrical potential, electricty stops flowing

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Batteries A battery is a device that converts chemical potential energy into electrical energy. Batteries consist of two electrodes and a substance that can conduct electricity

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Types of Batteries – Dry Cell A dry cell contains two electrodes and a moist paste to act as an electrolyte. Usually the electrodes are a carbon rod and the other is zinc A reaction occurs between the zinc and the paste, causing the zinc to build up a negative charge and the carbon to build a positive charge. Examples: AA, AAA, C, D cell batteries

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Types of Batteries – Wet Cell A wet cell consists of two electrode metal plates in a solution of sulfuric acid A wet cell battery consists of several cells connected together Example: Car Battery

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Resistance Resistance is the tendancy for a material to resist the flow of electrons. It converts electrical energy into heat and light. Is measured in ohms (Ω) Copper has a low resistance, it is used for wire in houses Tungsten has a high resistance and is used as a lightbulb filament

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Why would a thick wire have less resistance than a thin wire? It is easier for electrons to flow through the thick wire

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Ohm’s Law Current in a circuit is equal to the voltage difference divided by the resistance. I = V/R I = Current V = Voltage R = Resistance Twinkle Twinkle little star, I is equal to V over R

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A battery with a voltage of 6V is in a circuit with a lamp of resitance 2 Ω. What is the current in the circuit? V = 6 volts R = 2 ohms I = V/R = 6V/2 Ω = 3 amps

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32 amps of current are flowing through a circuit with a battery of 8V. What is the resistance of the circuit? I = 32 amps V = 8 volts I = V/R R = V/I = 8V/32amps =.25 Ω

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Power and Circuits

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Power Power is the rate at which work is done Electrical Power is the rate at which electrical energy is converted into another form of energy Different devices use electricity at different rates Power Rating of an appliance The amount of electrical energy needed to operate it Measured in watts (W) or kilowatts (kW) Power = current x voltage = I x V

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The current in an electric clothes dryer is 15A when it is plugged into a 240 V outlet. How much power does the clothes dryer use? I = 15 amps V = 240 V P = I x V = 15 A x 240 V = 3600 W = 3.6kW

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Electrical Energy Electrical energy is measured by an electric meter The amount used depends on the power required by the device and how long it is used. Measured in kilowatt hours (kWh) 1 kWh = 1 kW in 1 hour E= P x t kWh = kW x h

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A microwave oven with a power rating of 1200 W is used for.25 hours. How much electrical energy is used by the microwave? P = 1200 W = 1.2 kW t =.25 hours E = P x t = 1.2 kW x.25 hours =.3 kWh

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Circuits Two types of circuits Series Parallel

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Series Circuit The current only has one path to travel Amount of current is the same throughout the circuit Example: Christmas Lights Pasture Fence

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What happens if a bulb burns out? All the lights go out Since there is only one path, any break stops the current An open circuit is a circuit that is disconnected, with no flow

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Parallel Circuit Has many paths for the current to follow The amount of current can vary in each circuit because the resistance can vary. More current will flow through the path of least resistance Example Houses are wired in parallel

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Why are houses wired in parallel? So you can turn off a light in one room and not turn off all the lights. Each branch will have more current than in a series circuit

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Symbols

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Household Electricity Electricity flows from the power company to the electric meter at your house. Next it goes to a fuse box or circuit breaker From there it goes to the appliances in your house Standard voltage is 120V

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Interrupting the Circuit Fuse has a metal strip that melts when the current gets to high. It must be pulled out and replaced Circuit Breaker has a metal strip that bends when it gets to hot and breaks the circuit. It can be reset.

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