Chapter 7: Electricity

Chapter 7: Electricity

CHAPTER 7: ELECTRICITY CHAPTER 7-1: ELECTRIC CHARGE A. POSITIVE AND NEGATIVE CHARGE 1. Atoms contain 3 particles: protons, neutrons, and electrons. 2. Protons have a positive charge. 3. Neutrons have a neutral charge. 4. Electrons have a negative charge.

A. POSITIVE AND NEGATIVE CHARGES 5. An object is electrically neutral when the amount of protons equals the electrons. amount of 6. Some objects lose or gain electrons when

rubbed together. a. Gain electrons = negative charge b. Lose electrons = positive charge A. POSITIVE AND NEGATIVE CHARGE 6. Static Electricity Define: Accumulation of excess electric charge on an object. A. POSITIVE AND NEGATIVE CHARGES

The Law of Conservation of Charge states: charge can be transferred, but never created or destroyed. Charges exert forces. a. Opposite charges attract. Positive and negative charges. b. Like charges repel. Positive and positive or negative and negative.

A. POSITIVE AND NEGATIVE CHARGES c. The amount of electric charge depends upon: 1. Distance between objects.

As distance increases between objects, the force decreases. 2. Amount of charge. The force increases when the amount of charge increases. d. The strength of an electric force is much stronger than the gravitational force.

B. CONDUCTORS AND INSULATORS 1. Conductors a. Define: A material that allows electrons to flow easily. b. Metals make good conductors. c. Explains why electrical wires are made of copper metal.

B. CONDUCTORS AND INSULATORS 2. Insulators a. Define: A material where electrons cannot flow easily b. Examples: plastics, wood, rubber, glass, and silk c. Wiring is covered in a type of plastic to provide an insulating material.

C. CHARGING OBJECTS 1. Charging by contact a. Describe: Rubbing two materials together and transfer charge b. Example: clothes in the dryer tumble and rub against each other which leaves materials transferring

charge. C. CHARGING OBJECTS 2. Charging by induction a. Describe: The rearrangement of electrons on a neutral object caused by a nearby object b. Example: Rub a cloth on a balloon and give a negative charge. When brought

near your sleeve, the balloon repels the negatives in your sleeve and brings the positive towards the balloon where the balloon will now stick to the sleeve as the + sleeve and balloon are attracted. c. An electric field exerts a force on 3. THE ELECTROSCOPE

a. Define: A device that can detect the presence of electric charges. b. Made of two thin metal leaves attached to a metal rod with a knob. 4. LIGHTNING a. What is it? A large static discharge where a transfer of charge between 2 objects occur because a buildup of static.

b. How does it happen? In a storm cloud negatives move to the bottom, positives to the top as air masses swirl within. Eventually enough negative charge builds up to discharge to the positive ground. As it moves, the charges collide with atoms and molecules in the air which cause light to be emitted. 5. THUNDER a. What is it? The sound waves produced when lighting rips electrons off

atoms in the air and creates large amounts of thermal energy. b. How does it happen? As the air temperature surrounding rise (almost 25,000C), the air expands rapidly which produces a sound. 6. GROUNDING a. Absorption of an objects charges by contact with a much larger object.

b. An object connected to Earth, or the ground, by a good conductor is said to be grounded. c. Why use it? To provide a path for static discharge to reach earth prevents charges to build up. d. Where is it used? -metal lightning rod to a tall building - Plumbing fixtures (metal faucets), sinks, and pipes

CHAPTER 7-2: ELECTRIC CURRENT A. CURRENT AND VOLTAGE 1. Electric Current a. Define: net movement of electric charge in a single direction

b. Stream of flowing electrons i. Always move negative to positive A. CURRENT AND VOLTAGE DIFFERENCE 2. Electric Circuits a. The path along which an electric current travels.

b. Must always have a complete circle c. Must contain a conductor, voltage difference, and load. The circuit must be closed if electrons are to flow. d. Short circuit is when two wires cross.

3. PARTS OF A CIRCUIT Label 1. 2. 3. 4. 5. 6. 7. 8.

A. CURRENT AND VOLTAGE DIFFERENCES 4. Measuring Electron Flow a. Electric current flow of electrons (electrons/second) Water flows in gallons/second b. Coulomb = amount of charge from 6.25 billion

electrons i. 6.25 x 1018 electrons A. CURRENT AND VOLTAGE DIFFERENCE c. Ampere is the unit of current i. 1 amp = 1 coulomb/sec d. Ammeter- device to measure how many

electrons flowing through an object. i. Measures electric current. e. 1 ampere of current = 1 coulomb of electrons flowing through a wire per second. f. 1 amp to light a 100 watt lightbulb per A. CURRENT AND VOLTAGE DIFFERENCE

5. What pushes electron through a wire? (What cause current to flow?) a. Electrons flow from an area of high concentration (- charge) to an area of low concentration (+ charge). b. Electrons flow from the negative to the positive. c. The greater the difference between the high (-) and the low (+), the greater the pressure will be which increases voltage.

d. Electrical pump (battery/generator) A. CURRENT AND VOLTAGE DIFFERENCE 6. Voltage Difference a. This is the force that causes electrons to flow. b. The difference between high (-) and positive (+)

A. CURRENT AND VOLTAGE DIFFERENCE c. Volt- amount of electrical pressure needed for 1 coulomb of charge to do 1 joule of work. d. Pressure is needed to keep electrons flowing. e. Volts is measuring the pressure difference between the negative and positive.

A. CURRENT AND VOLTAGE DIFFERENCE f. Voltmeter- device that measures difference of electrical pressure. 2 measurements taken with a voltmeter 1) Voltage total VT = total voltage produced by the source. 2) Voltage drop VD = voltage difference before and after a resistor (anything that produces heat/light). A. CURRENT AND VOLTAGE DIFFERENCE

g. Voltage drop tells you the pressure used to go through the resistor. h. Increased volts will increase electrical pressure which will raise current. B. RESISTANCE Define: measure of how difficult it is for electrons to flow through a material.

1. Slows down the flow of electrons. B. RESISTANCE 2. Effected by opposition to flow. a. Thickness thicker less resistance, more current b. Composition Gold = least resistance (gold plated), Copper

strands are better because more surface area for electrons to flow. c. Length more resistance in long wire, use as short as possible d. Temperature cold wire has less resistance, electrons vibrate less B. RESISTANCE

3. Best wire for less resistance: thick, gold stranded, short, and cold. B. RESISTANCE 4. Ohm= unit of electrical resistance (opposition to flow) 5. Volts and resistance affects amount of electron flow through

the wire (current) 6. pressure, current, resistance C. OHMS LAW 1. Relationship between volts, amps, and ohms

2. V = I x R a. V = voltage difference; volts b. I = current; amps c. R = resistance; ohms 3. 1 volt of pressure cause 1 amp of current to move through 1 ohm of resistance. D. PRACTICE PROBLEMS

1. What is the voltage in a circuit that has a current of 2.4 A and a resistance of 4.0 ? D. PRACTICE PROBLEMS 2. A Walkman uses a current of 2.0 A and has an internal resistance of 3.0 , how many 1.5 V batteries are required? D. PRACTICE PROBLEMS 3. A stove uses a power source of 240 V and draws a current of 5.0 A, what is the resistance in the stove?

D. PRACTICE PROBLEMS 4. You have five 1.5 V batteries, a 1 bulb, a 2 bulb, and a 3 bulb. Draw a circuit you could built to create each of the following currents. There may be more than one possible answer. a. 1 amps

b. 3 amps CHAPTER 7-3: ELECTRICAL ENERGY TYPES OF CIRCUITS A.Series Circuit 1. One path for electros to flow from negative to positive. 2. When any part of the series circuit becomes open, no

current will flow through the circuit. A burned-out bulbs or switch can open a circuit. 3. Example - Holiday lights B. FOUR CHARACTERISTICS OF SERIES CIRCUIT 1. Current (amps) will be the same through the circuit.

a. IT = I are the same 2. Total Resistance RT (ohms) is found by adding the resistance of all separate resistors a. RT = R1 + R2 + R3 RT = VT/I B. FOUR CHARACTERISTICS OF SERIES

CIRCUIT 3. Voltage Drop is the voltage (pressure) used to push the current through a particular resistance. a. The sum of the voltage drops will equal the original voltage source VT = VD1 + VD2 + VD3

4. If you break the circuit at anyone place, current ceases to flow. C. PARALLEL CIRCUIT 1. Circuit with more than one path for electrons to flow from negative to positive. 2. If one path is broken electrons

will follow another path. 3. Houses, automobiles and most electrical systems use parallel wiring so individual parts can be turned off without affecting the D. FOUR CHARACTERISTICS OF PARALLEL CIRCUIT

1. Current (amps) will vary throughout the circuit. a. The sum of the currents in all of the resistors equals the total current. b. IT = I1 + I2 + I3 2. Total Resistance RT (ohms) is found by adding the resistance of all separate resistors.

a. 1/RT = 1/R1 + 1/R2 + 1/R3 D. FOUR CHARACTERISTICS OF PARALLEL CIRCUITS 3. Voltage across each resistance is the same 4. If you break the circuit at anyone place, current will

continue to flow through the other branches. CIRCUIT SUMMARY Series Same = amps Sum = Rt (ohms) Sum = Vt (volts)

One path Parallel Sum = amps Sum = 1/Rt (ohms) Same = Vt (volts) Multiple paths CHAPTER 7-3: ELECTRICAL POWER AND

ENERGY A. ELECTRICAL POWER 1. Electrical power is the rate at which electrical energy is converted to another form of energy. 2. Electrical energy is converted to mechanical energy as the blades in a

fan turn. 3. Electrical energy is converted to A. ELECTRICAL POWER 4. Appliances are often labeled with a power rating that describes how much power the appliance uses.

A. ELECTRICAL POWER 5. Equation: Electrical power = current x voltage difference P=IV PRACTICE PROBLEMS

a. An electric space heater draws 29 A of current when plugged into a 120 V outlet. What is the power rating of the heater? PRACTICE PROBLEMS b. A color television has a power rating of 320 W. How much current is in the television when it is connected across

120 V? B. ELECTRICAL ENERGY 1. Electric companies charge by the amount of electrical energy used, rather than by the electric power used. 2. Measured in kilowatt hours (kWh)

B. ELECTRICAL ENERGY 3. Equation: Electrical energy = electrical power x time E=Pt PRACTICE PROBLEMS a. Calculate the energy (in kilowatts per

hour) used by a 3000 W water heater that operates continuously for 30 minutes. PRACTICE PROBLEMS b. How much power is used by an electric hair dryer that uses 0.15 kWh of energy during 6 minutes of use?

C. COST OF USING ELECTRICAL ENERGY 1. Cost of an appliance can be calculated by multiplying electrical energy used by the amount the power company charges for each kilowatt hour. 2. If a 100 W light bulb is left on for 5 hours, what is the amount of energy used? 3. If the power company charges $0.10 per kWh, the cost of using the bulb for 5 hours is?

PRACTICE PROBLEMS a. A hair dryer is used for 7.5 hours one month. It uses 600 watts of power, on average. How much electrical energy does the hair dryer use in a month? How much would it cost to use the hair dryer each month if the rate charged by the electric company is $0.09 per kWh? PRACTICE PROBLEMS b. A stereo is used for 90 hours per month. It costs $0.88

to run the stereo each month. If the electric company charges $0.09 per kWh, what electric energy is used by the stereo? What power is used?

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