Section 20.2- Electric Current and Ohm’s Law

I. Electric Current (p. 604)

            A. Electric current- the continuous flow of electric charge, usually following a path.

            B. There are two types of electric current

                        1. Direct current (DC)- charge flows only in one direction  (battery-op. devices)

                        2. Alternating current  (AC)- a flow of electric charge that regularly reverses

                            its direction (the most used in buildings like the school)

                        3. While electrons (-) are what actually flow, scientists define current as the

                             direction in which positive charges would flow.

                        4. The SI unit for current is the ampere (A), or amp (1 A = 1 coulomb per second)

II. Conductors and Insulators (p. 605)

            A. Electrical conductor- a material through which charge can flow easily.

                        1. Metals are good electrical conductors because the ions have electrons that

                            are not bound to them and are free to move, conducting charge. (Copper, silver, etc.)

            B. Electrical insulator- a material through which charge cannot flow easily.

                        1. These can surround conductors for protection (examples- wood, plastic, rubber, air)

III. Resistance (p. 605) - opposition to the flow of charges in a material.

A.     Electrons can collide with other electrons or ions as they move, converting

some energy to thermal energy and reducing current

B. The SI unit for resistance is the ohm

            C. A material’s thickness, length, and temperature affect its resistance

                        1. Thicker material à lower resistance (more space for traveling)

                        2. Longer wire à greater resistance (more distance to travel)

                        3. Higher temperature à greater resistance (more collisions)

                        4. To summarize: The best wires for conducting are thick, short, and cold.

            D. Superconductor- a material that has almost zero resistance when it is

                cooled to low temperatures.

IV. Voltage (p. 606)

            A. In order for charge to flow in a conducting wire, the wire must be connected in a

                 complete loop that includes a source of electrical energy.

            B. Potential difference (also called Voltage)- the difference in electrical

                 potential energy between two places in an electric field.

                        1. Potential difference is measured in joules per coulomb, or volts.

                        2. Potential energy of a charge depends on its position in an electric field.

                        3. Charges flow from higher to lower potential energy.

            C. Voltage sources

                        1. A source of voltage must do work to increase the potential energy of electric

                            charges.

                        2. Battery- a device that converts chemical energy to electrical energy

                                    a. Terminals connect to wires in a circuit.

                                    b. One positive terminal, one negative terminal

                                    c. A potential difference is maintained across the terminals.

V. Ohm’s Law (p. 607)

            A. Ohm’s law- the voltage (V) in a circuit equals the product of the

                 current (I) and the resistance (R).

            B. V = I x R                            

            C. Increasing the voltage increases the current, but increasing the resistance

                 decreases the current if voltage is constant.

            D. A multimeter can be used to measure current, voltage, and resistance.

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Section 20.1- Electric Charge and Static Electricity

I. Electric Charge

            A. Electrical energy is the energy associated with electric charges.

            B. Electric charge is a property that causes subatomic particles such as protons and

                electrons to attract or repel each other.

            C. There are two types of electric charges, and just about everything is affected by these

                        1. Positive electric charge- protons have this

                        2. Negative electric charge- electrons have this

            D. In atoms, electrons are arranged in clouds around a positive nucleus.

                        1. An excess or shortage of electrons produces a net

                            electric charge

                        2. Atoms can gain and/or lose electrons

                        3. If there are more electrons than protons, the atom is a negative ion.

                        4. If there are more protons than electrons, the atom is a positive ion.

                        5. If the number of protons and electrons are equal, the atom is neutral.

            E. The SI unit of electrical charge is the coulomb (C)

II. Electric Forces

            A. Like charges repel each other, and opposite charges attract

            B. Electric Force- the force of attraction or repulsion

                 between electrically charged objects.

            C. Electric force is directly proportional to the net charge on each object

                        1. Greater difference between the charges, more force

                        2. Smaller difference between the charges, less force

            D. Electric force is inversely related to the square of the distance between the objects.

                        1. Farther apart objects are, less force

                        2. Closer together objects are, more force

            E. Electric forces cause atoms to form bonds with other atoms

III. Electric Fields

            A. Electric field- the effect of an electric charge on the other charges in the

                 space around it.

            B. The strength of an electric field depends on the amount of charge that

                 produces the field and on the distance from the charge.

IV. Static Electricity and Charging

            A. Static electricity- the study of the behavior of electric charges, including

                 how charge is transferred between objects

            B. Charge can be transferred by friction, by contact, and by  induction

                        1. The law of conservation of charge- the total charge in an

                            isolated system is constant (charge before transfer = charge after).

                        2. Charging by friction- when two objects rub, one object gains

                            electrons, the other object loses electrons

                        3. Charging by contact- when two objects touch, one gains

                            electrons, the other loses electrons.

                        4. Charging by induction- a transfer of charge without contact

V. Static Discharge

            A. Static discharge occurs when a pathway through which charges can

                 move forms suddenly.

            B. Charges cannot move through air unless a pathway in the air becomes charged.

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Section 16.2- Heat and Thermodynamics

I. Conduction (p. 479)

            A. Conduction- the transfer of thermal energy with no overall transfer of matter

                        1. Occurs within a material or between materials that are touching

                        2. example- “Newton’s cradle”

                        3. Conduction in gases is slower than in liquids and solids because the

                            particles in gases collide less often.

                        4. In metals, conduction is faster because some electrons can move about

            B. Thermal Conductors (p. 480)

                        1. A thermal conductor is a material that conducts thermal energy well.

                        2. examples: metal of pots and pans, tiles on floor

            C. Thermal Insulators (p. 480)

                        1. A thermal insulator is a material that conducts thermal energy poorly.

                        2. Examples: styrofoam, wool clothing, air

II. Convection (pp. 480-481)

            A. Convection is the transfer of thermal energy when particles of a

                 fluid move from one place to another.

                        1. Particles in a fluid can transfer thermal energy from a hot

                            area to a cold area.

                        2. Example- convection ovens- warm air at bottom rises to the top of the oven

            B. Convection current- when a fluid circulates in a loop as it alternately

                 heats up and cools down.

III. Radiation (p. 481)

            A. Radiation is the transfer of energy by waves moving through space.

                        1. This is how the sun heats our earth

                        2. Heat lamps are also an example of radiation

            B. All objects radiate energy

                        1. As an object’s temperature increases, the rate at which it

                            radiates energy increases.

                        2. Example- heating coil on an electric stove

IV. Thermodynamics (pp. 482-483)

            A. Thermodynamics- the study of conversions between thermal energy

                 and other forms of energy

                        1. People responsible for research:

                                    a. Count Rumford

                                    b. James Prescott Joule

            B. The First Law of Thermodynamics (p. 482)

                        1. Energy is conserved. (applied to work, heat, and thermal energy)

                        2. If energy is added to the system, it either increases the thermal

                            energy of the system or does work on the system.

            C. Second Law of Thermodynamics (p. 482-483)

                        1. Thermal energy can flow from colder objects to hotter

                            objects only if work is done on the system.

                        2. Heat engine- any device that converts heat into work.

                                    a. efficiency is always less than 100%

                                    b. waste heat- thermal energy that is not converted into work,

                                        but is lost to the surrounding environment

                                    c. Heat engines are more efficient when there’s a greater difference

                                        between internal temperature (hot) and external

                                        temperature (cooler)

                                    d. Disorder in the universe as a whole is always increasing

            D. Third Law of Thermodynamics (p. 483)

                        1. Absolute zero cannot be reached.

                        2. In theory, heat engines would be 100% efficient if the temperature

                            outside of the engine were absolute zero, but this cannot

                            happen.

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Section 16.1- Thermal Energy and Matter

I. Work and Heat (p. 475)

            A. Heat is the transfer of thermal energy from one object to another because of a

                 temperature difference.

            B. Heat flows spontaneously from hot objects to cold objects.

II. Temperature (p. 475)

            A. Temperature is a measure of how hot or cold an object is compared to a reference point.

            B. Temperature is related to the average kinetic energy of the particles

                 in an object due to their random motions through space.

                        1. As an object gains heat, its particles usually move faster.

                        2. When particles move faster, their kinetic energy increases.

            C. Collisions transfer thermal energy from hot to cold objects

                        1. Hotter objects lose energy in collisions; cooler objects gain energy in collisions

III. Thermal Energy (p. 475)

            A. Thermal energy is the total potential and kinetic energy of all the particles in an object.

            B. Thermal energy depends on mass, temperature, and phase of an object.

                        1. The larger the mass, the more thermal energy

                        2. The higher the temperature, the higher the kinetic energy of the particles, and

                            the greater the thermal energy.

                        3. Phase effects (solids, liquids, and gases)

                                    a. Gases have more thermal energy than liquids

                                    b. Liquids have more thermal energy than solids

            C. Phase changes

                        1. Gain in thermal energy

                                    a. boiling- liquid to gas at boiling point

                                    b. evaporation- liquid to gas at any temperature

                                    c. sublimation- solid to gas

                                    d. melting- solid to liquid

                        2. Loss of thermal energy

                                    a. freezing- liquid to solid

                                    b. condensation- gas to liquid

                                    c. frosting- gas to solid

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Energy Resources

I.       Nonrenewable Energy Resources

Exist in limited quantities and cannot be replaced except over millions of years

A.    Fossil fuels (Oil, Natural Gas, Coal)

B.    Advantages

1.    Available

2.    Inexpensive

C.    Disadvantages

1.    Formation

a.    Underground from remains of living things

b.    Takes billions of years

c.    Supply- Controlled by small, less-than-stable area of world, Getting depleted

2.    Pollution

II.     Renewable Energy Resources

Resources that can be replaced in a relatively short period of time.

A.    General Benefits- Unlimited supply, Less pollution

B.    General Drawbacks- Expense, Newer technology

C.    Renewable options

1.    Hydroelectric

a.    Energy obtained from flowing water

(1)    water flowing downhill, PEgrav converted to into KE

(2)    KE turns turbines connected to electric generators

(3)    Often relies on dams to increase PE

b.    Advantages- low cost, lack of pollution, renewable

c.    Disadvantages- environmental problems, Sites

2.    Solar

a.    Sunlight converted into usable energy

(1)    Passive- Light passes in to heat buildings

(2)    Active

(a)    light heats water, which is used

(b)    photovoltaic cells (sunlight turned directly into electricity)

b.    Advantages- nonpolluting, renewable

c.    Disadvantages- needs sunlight, expense

3.    Geothermal

a.    Thermal energy beneath Earth's surface generates electricity

               (heats water, steam drives turbines)

b.    Advantages- clean, energy is there already

c.    Disadvantages- difficult to harness, location

4.    Wind

a.    Wind drives turbines

b.    Advantages- Clean, renewable

c.    Disadvantages- needs wind, need many turbines

5.    Biomass

a.    Chemical energy stored in living things

(1)    Converted to thermal by burning

(2)    Converted to fuel

b.    Advantages- it’s available, much is waste

c.    Disadvantages- burning makes pollutants. Must replenish forests.

6.    Hydrogen Fuel Cells

a.    generates electricity by reacting hydrogen with oxygen

b.    Advantages- clean! Efficient.

c.    Disadvantages- expensive, still being developed.

7.    Nuclear Fusion

a.    Fusing nuclei to produce energy

b.    Advantages- makes much energy, technology is available

c.    Disadvantages- radioactive wastes, nuclear danger, environmental effects

III.    Conserving Energy Resources

Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use

A.    Reducing energy needs

1.    Energy conscious decisions

B.    Increasing efficiency of energy use

1.    Energy efficient cars, appliances, light bulbs, etc.

2.    Improved technology

3.    Involves expense