Electricity A Electric Charge 1 Static electricity is

Electricity A. Electric Charge 1. Static electricity is the accumulation of excess electric charges on an object. a. More e¯ = negative charge b. More protons = + charge 2. Charge is conserved (e¯ move from one object to another).

3. Law of Charges a. Opposite charges attract. b. Like charges repel. 4. Electric fields a. Electric fields exert force on objects within the field. b. Weaker with distance.

6. Lightning a. Large static discharge between the earth and clouds. b. Lightning was found to be static electricity by Ben Franklin. 7. Grounding a. Conductive path to Earth. b. Lightning rods & plumbing.

http: //www. youtube. com/watch? v=zp. UHC 21 FOE 4

1. Stay AWAY from the water and metal objects. 2. If there is a nearby car, get inside it! 3. If you can’t find shelter, stay away tall objects. “If only isolated trees are nearby, your best protection is to crouch in the open, keeping twice as far away from Isolated trees as the trees are high. ” 4. “If your skin tingles or your hair stands on the end, a lightning strike may be about to happen. Crouch down on the balls of your feet with your feet close together. Keep your hands on your knees and lower your head. Get as low as possible without touching your hands or knees to the ground. DO NOT LIE DOWN!”

B. Electric Current 1. The reason electric charge flows from one place to another is voltage. HIGH LOW a. Voltage is the difference in electrical potential between two places where e¯ are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V).

2. The flow of electric charge is called current. a. Current is measured in amperes, or amps (A). b. Voltage causes current.

4. Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells

9 V 9 V Battery

• Therefore, compared to a 1. 5 Volt battery, the electrons of a 9 Volt battery have a much greater “desire” to flow from one end to the other >

5. Resistance a. Opposition to the flow of e¯. b. It changes electrical energy into thermal energy and/or light. c. Measured in ohms. d. Conductors have less resistance than insulators.

e. Wire resistance greater for: 1) Longer wires 2) Thinner wires 3) Higher temperatures

You can imagine a resistor in a circuit as a narrow pipe in a plumbing system! As the water reaches this spot, less will be able to flow through and the current will be reduced.

E. Light Bulbs 1. Incandescent a. Have a tiny filament that resists the flow of electrons. b. The filament gets hot and glows to produce light. c. Very hot and inefficient.

2. Fluorescent a. Filled with gas and coated with phosphor. b. Electricity excites the gas making it give off U-V rays. c. Phosphor absorbs U-V rays and glows to make light. d. Very cool, efficient, and last a long time.

Electrical Energy Consider a simple circuit: The job of the battery is to convert ______ energy into _____ energy… The job of the bulb is to convert the _____ energy it receives from the battery into ______ energy. Words – electrical (x 2), light, chemical 21/12/2021

C. Electrical Circuits 1. A circuit is a conducting path. 2. Series circuit a. One path b. Any break & all devices go out c. Current is the same throughout the circuit

3. Parallel circuit a. Multiple paths b. A break in one branch & the other branches stay on c. Voltage is the same in each branch, but current and resistance may be different

Comparison of series and parallel circuits The same voltage battery Notice the brightness of the bulbs

6. Ohm’s law Voltage Resistance Current = V I R

4. Household circuits a. Mostly parallel. b. 120 Volts in the U. S. 220 Volts in Europe (Why? ) c. More devices plugged in a circuit mean more current. d. More current means more heat in the wiring.

5. Electrical safety devices a. Fuses - one time use. b. Circuit breakers - can be reset and reused. c. When the current limit of the wire is reached, the Fuse or Circuit breaker “breaks the circuit, preventing fires.

D. Electric Power and Energy 1. Electrical power is the rate at which electricity is converted into another form of energy. a. Power = current x voltage b. Unit is the watt or kilowatt. 2. Electrical energy a. Energy = power x time b. Unit is the kilowatt-hour. (1000 watts for 1 hour) c. This is what we buy from the electric company.

Fuels 21/12/2021 A “fuel” is something that can be burned to release heat and light energy. The main examples are: Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.

Power stations Boiler Transformer Turbine Cooling tower 21/12/2021 Generator

What does each part do? 21/12/2021 The boiler is where the fuel is burnt to boil water The steam from the boiler is used to turn a turbine The turbine is connected to the generator, which acts like a dynamo – it generates electricity out of movement The steam is cooled down and turned back into water in the cooling tower

Energy Transfer diagrams 21/12/2021 Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram: “Input” energy 100 J/s electrical energy “Output” energy 20 J/s light energy 80 J/s heat energy (given to the surroundings)

Example questions Consider a kettle: 2000 J/s electrical energy Sound energy Wasted heat Heat to water 1) Work out each energy value. 2) What is the kettle’s efficiency? 21/12/2021 Consider a computer: 150 J/s electrical energy 10 J/s wasted sound 20 J/s wasted heat Useful light and sound 1) How much energy is converted into useful energy? 2) What is the computer’s efficiency?