Electricity, Ohm’s Law and Circuits Physical Science Unit 8 V = I R Ohm’s Law

Electricity Particles in the atom: protons,neutrons,electrons *Protons and neutrons are locked in the nucleus; electrons orbit the nucleus and can be removed Unit 8, Physical Science

*Objects become charged due to the movement of electrons *An object gaining electrons will become negatively charged plastic strip fur or wool e-e- + + rub Plastic strips electrons from fur; plastic becomes negatively charged ________

plastic strip Instead, silk strips electrons from the plastic Silk becomes negative, and the plastic becomes positive silk rub e-e *Objects become positively charged by losing electrons

More vocabulary: conductor: insulator: a material through which electrons can pass easily; ex: metals a material through which electrons cannot travel; ex: glass, wood, rubber electrons are loosely held in atom and can easily be removed electrons are locked in the atom and cannot be removed easily

If electrons are placed on an insulator, they cannot move on its surface; they are locked in place e-e- x electron stays where it is placed, on an insulator static electricity: electricity that does not move

Current Electricity vocabulary: Voltage: Current: Resistance:

Ohm’s Law R = V I R V I V = I = V = I R Ohm’s Law A V Ω Units in red

Schematic Symbols for Drawing Circuits + - V A

Series Circuit: (1)Current is the same everywhere VTVT V1V1 V2V2 V3V3 (2) Voltage is divided between bulbs ITIT I1I1 I2I2 I3I3 (3) If one bulb burns out, only one possible path for current

Parallel Circuit: (1)Current is divided between bulbs VTVT V1V1 V2V2 V3V3 (2) Voltage is the same everywhere (3) If one bulb burns out, ______________________ I1I1 I2I2 I3I3 ITIT more than one possible path for current

ITIT I1I1 I2I2 I3I3 I4I4 I T = I 1 + I 2 + I 3 + I 4 - When current passes through wires, - As more resistors are added to a parallel circuit, _______ ______________________________________________ wires could overheat and cause a fire - Use a fuse _______________

thin wire Fuses As current passes through the fuse, the thin wire heats up When current reaches a certain value, __________ metal contacts insulator

ITIT I1I1 I2I2 I3I3 I4I4 Fuses are in series with the rest of the circuit ; when thin wire melts, _________ Schematic symbol for fuse: Schematic symbol for ____________ Circuit breakers protect circuits also, and ___________ circuit breaker

Power P = I V ex. Find the power generated in the light bulb in the earlier example ( voltage = 120 V, current = 0.50 A )

Cost of Power Power is generated in power plants and transported to our homes by transmission lines We are charged for the energy we use P = W t Energy t = Energy = P t Unit: watt secondkilowatt hour kW h

Cost of Power Example Appliance: Microwave Power rating: 1100 W (a) P = I V (b) V = I R

(c) Estimate that it is in use 10 minutes a day 10 min x 30 days = 300 min = 6 hr

Example 2 1. Wattage of light bulb = 60 W 2. Bulb is on 4 hrs a day

6. Wattage of CFL = 13 W Bulb is on 4 hrs a day 7

Review from Electrostatics Lab: 1. Like charges repel, opposite charges attract Neutral objects are attracted to charged objects; for either charge -+ why?

Bring Negatively Charged Rod Near a Neutral Ball 2. Electrons are repelled to far side repulsion 4. Strip and ball are both negative 3. Electrons move from strip to ball Positives are closer, ball is attracted to strip Items are touching

Bring Positively Charged Rod Near a Neutral Ball 2. Electrons are attracted to near side repulsion 4. Strip and ball are both positive 3. Electrons move from ball to strip Negatives are closer, ball is attracted to strip