Presentation on theme: "Electricity A. Electric Charge"— Presentation transcript:
1 ElectricityA. Electric Charge1. Static electricity is the accumulation of excess electric charges on an object.a. More e¯ = negative chargeb. More protons = + charge2. Charge is conserved (e¯ move from one object to another).
2 3. Law of Chargesa. Opposite charges attract.b. Like charges repel.4. Electric fieldsa. Electric fields exert force on objects within the field.b. Weaker with distance.
3 5. Transferring electric charge a. Conductors: e¯ move easily.b. Insulators: hold e¯ tightly.c. Contact charging is done when two materials are rubbed together (best with insulators).d. Charging by induction is done when one charged object induces a charge on another.
4 6. Lightninga. Large static discharge between the earth and clouds.b. Lightning was found to be static electricity by Ben Franklin.7. Groundinga. Conductive path to Earth.b. Lightning rods & plumbing.
5 8. The electroscope can be used to detect electric charge
6 b. Voltage is the “push” that makes electric charges move. B. Electric Current1. The reason electric charge flows from one place to another is voltage.HIGHLOWa. 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).
7 2. The flow of electric charge is called current. a. Current is measured in amperes, or amps (A).b. Voltage causes current.3. The amount of electric charge is measured in coulombs.a. 1 coulomb is the charge carried by 6.24 x 10^18 e¯.b. 1 amp is 1 coulomb per sec.
8 4. Batteries are e¯ pumps.a. They provide a voltage difference to a circuit.b. Types: wet-cells & dry-cells
9 5. Resistancea. 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.
12 C. Electrical Circuits1. A circuit is a conducting path.2. Series circuita. One pathb. Any break & all devices go outc. Current is the same throughout the circuit
13 Series Circuit Concepts (assuming 3 resistors)RTOTAL = R1 + R2 + R3V drop for each R is VX = I • RXso, VTOTAL = I • R1 + I • R2 + I • R3or, VTOTAL = I • (R1 + R2 + R3)since I = V ÷ Rthen… ICIRCUIT = V ÷ (R1 + R2 + R3)
14 3. Parallel circuita. Multiple pathsb. A break in one branch & the other branches stay onc. Voltage is the same in each branch, but current and resistance may be different
15 Parallel Circuit Concepts (assuming 3 paths)V is the same everywhere in the circuitITOTAL = I1 + I2 + I3since ITOTAL = V ÷ R and I1 = V ÷ R1then V ÷ R = V ÷ R1 + V ÷ R2 + V ÷ R3RTOTAL R1 R2 R3
16 Comparison of series and parallel circuits The same voltage batteryNotice the brightness of the bulbs
17 4. Household circuitsa. Mostly parallel.b V in the U.S.c. More devices plugged in a circuit mean more current.d. More current means more heat in the wiring.
18 5. Electrical safety devices a. Fuses - one time use.b. Circuit breakers - can be reset and reused.
19 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 voltageb. Unit is the watt or kilowatt.2. Electrical energya. Energy = power x timeb. Unit is the kilowatt-hour.(1000 watts for 1 hour)c. This is what we buy from the electric company.
20 E. Light Bulbs1. Incandescenta. 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.
21 2. Fluorescenta. Filled with gas and coated with phosphor.b. Electricity excites the gasmaking 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.