ELECTRICITY Intro to Agriculture AAEC PV Spring 2015

ELECTRICITY Intro to Agriculture AAEC – PV Spring 2015

POSITIVE & NEGATIVE CHARGES Atoms have protons (positive) and electrons (negative); neutrons are neutral When objects have an excess of electrons, they become negatively charged

ELECTRIC FIELDS Electric fields surround every charge and can act upon other objects (even without touching them) The force created by this field can either ATTRA REPEL

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

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

WHAT IS ELECTRIC CURRENT Net movement of electric charges (electrons) in a single direction Measured in amperes

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.

WHAT IS A POTENTIAL DIFFERENCE? The force that causes electrons to flow Electric charge flows from a higher voltage to a lower voltage

CIRCUIT Circuit – closed path that electric current follows This flow of electrons can power things like light bulbs

RESISTANCE 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

QUICK RECAP 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.

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

OHM’S LAW Ohm’s Law – the current (I) in a circuit equals the voltage difference (V) divided by resistance (R)

PRACTICE PROBLEMS 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.

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

CIRCUITS 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

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.

PARALLEL CIRCUIT 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!

A SWITCH CAN BREAK A CIRCUIT AND TURN A DEVICE ON OR OFF. Would this switch still work?

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.

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

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

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

COST OF ELECTRICITY 1) Most companies charge by the amount of energy used 2) This is measured in kilowatt hours (k. Wh) 3) Each light bulb in your house costs money to leave on! 4) Meters outside your house measure how much energy is used

WHAT IS THE DIFFERENCE BETWEEN ALTERNATING CURRENT AND DIRECT CURRENT? AC = alternating current DC = direct current Direct Current is found in simple circuits like a battery powered flashlight.

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.

SHOW WHAT YOU KNOW! 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. 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 ______.