ELECTRICITY Electric Fence Experiment.

Transcription

1 ELECTRICITY Electric Fence Experiment. Can you guess what will happen? What would life be like without electricity? List 4 things that you would miss the most: 1) 2) 3) 4)

2 Positive and Negative Charge atoms have protons (positive) and electrons (negative); neutrons are neutral when objects have an excess of electrons, they become negatively charged Opposites attract Objects with the same charge repel

3 Diagram of an Atom Protons and Neutrons are in the center Electrons orbit around the outside -- these are SUBatomic particles Bohr model of the atom Label the protons, neutrons, electrons, and the nucleus

4 Static electricity occurs when electrons transfer to your clothes or hair and give them a charge. When you touch something, the charge is released, causing a "jolt" Each hair is negatively charged and repels other hairs. Or balloons stick to the cat

5 Electric fields surround every charge and can act upon other objects (even without touching them) The force created by this field can either attract or repel

6 Conductor - material in which electrons can flow freely Ex. Metals, such as copper Insulator - electrons do not move easily through Ex. plastic, rubber

7 What is Grounding? Buildings often install lightning rods, which provide a path for electrons to take to the earth, bypassing the building and sensitive electric equipment

8 What Is Electric Current? - net movement of electric charges (electrons) in a single direction - measured in amperes

9 This diagram shows a simple LED driver circuit. When the battery is connected the positive end of the battery pulls electrons from the negative end of the battery and through the circuit. This circuit has three basic properties: voltage, current, and resistance.

10 What Is a Potential Difference? - the force that causes electrons to flow - electric charge flows from a higher voltage to a lower voltage

11 Circuit = a closed path that electric current follows This flow of electrons can power things like light bulbs

12 Resistance = tendency for material to oppose the flow of electrons -- electric current loses energy as it flows -- resistance is measured in OHMS * Copper has a low resistance, hence it is used for household wiring and other electronics

13 STOP AND THINK 1. A positively charged subatomic particle is negatively charged subatomic particle is 2. Amperes are used to measure 3. A closed path that electrons (current) can flow through is a: 4. Materials that current can flow through easily are called: 5. OHMS are used to measure the of a circuit.

14 As the length of a wire increases, so does its resistance As the wire becomes thinner, its resistance increases the thin wire in a tungsten light bulb glows due to this resistance

15 Ohm's Law -- the current (I) in a circuit equals the voltage difference (V) divided by resistance (R)

16 Quick Calculations: 1. What is the current of a circuit with a voltage difference of 20 volts and a resistance of 10 ohms. 2. What is the Voltage difference in a circuit with a resistance of 11 ohms, and a current of 2 amperes.

17 1. What is the center of an atom called? 2. Electrons are attracted to 3. Electrons move from the to the side of a battery. 4. What is the most common metal used in wiring? 5. How many volts are in an AA battery? 6. How many volts are in a wall outlet? 7. A device used to turn electricity on and off is a 8. In which type of circuit can you turn a light off and the other will stay on? [ series / parallel ]

18 Circuits How many electrical devices can you see in this room? Name 2. Circuits have: 1) source of voltage difference (battery or outlet) 2) device that uses the energy (light) 3) conductors (wires) form a closed path to device

19 Series Circuit Example: A string of christmas lights, when one light burns out, no lights will work. Why? Because that burned out bulb breaks the circuit to all the bulbs. Each bulb along the path shares the voltage, so the bulbs may appear dim.

20 Parallel Circuits Series circuits aren't a good way to wire a house. If you turned off one light, then all the lights would go out. Parallel circuits contain two or more branches Disadvantage: Even when you turn a light off, current continues to flow through the system. This is why you shouldn't stick a fork in an electric socket!

21 A switch can break a circuit And turn a device on or off Would this switch still work?

22 Identify the type of circuit:

23 What is a fuse? Fuses contain a tiny piece of metal that melts if the current gets too high - this breaks the circuit. Too many appliances on in one room can overload the circuit and blow a fuse.

24 Where does electricity come from? Most electricity comes from converting heat energy into electrical energy - burning fossil fuels such as coal and natural gas. Some electricity is generated from dams, and nuclear reactors

25 How do dams generate electricity? As water flows through the dam it spins turbines, which will create electricity. These are referred to as: HYDROELECTRIC DAMS

26 How are dams built? How do they hold all that water back? What happens when dams fail?

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28 Cost of Electricity 1) Most companies charge by the amount of energy used 2) This is measured in kilowatt hours (kwh) 3) Each light bulb in your house costs money to leave on! 4) Meters outside your house measure how much energy is used Check out:

29 What is the difference between alternating current and direct current? Check out org/wgbh/amex/edison/sfeature/acdc. htmlhttp:// org/wgbh/amex/edison/sfeature/acdc. html AC = alternating current DC = direct current Direct Current is found in simple circuits like a battery powered flashlight.

30 Alternating Current The direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC current/voltage source. AC power is used in homes and business. It's cheaper and easier to make devices for AC power, and you can easily increase and decrease the current.

31 QUIZ TIME

32 1. What happens when an object has an excess number of electrons? 2. Name something that is a conductor: 3. What unit is electric current measured in? 4. What unit is electric energy measured in (think power bill)? 5. The force that causes electrons to flow is the difference.

33 6. Is the image showing a parallel or series circuit? 7. Where does the electricity come from that powers your house? 8. What causes a fuse to be blown? 9. Law can be used to calculate voltage. 10. Resistance is the tendency for to oppose the flow of.

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