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Unit Electricity

Unit Electricity. I. Electric Charge Static Electricity Conductors Insulators Electroscope. What do these have in common?. A. Static Electricity. Static Electricity the net accumulation of electric charges on an object Electric Field

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Unit Electricity

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  1. Unit Electricity I. Electric Charge Static Electricity Conductors Insulators Electroscope

  2. What do these have in common?

  3. A. Static Electricity • Static Electricity • the net accumulation of electric charges on an object • Electric Field • force exerted by an e- on anything that has an electric charge • opposite charges attract • like charges repel

  4. A. Static Electricity • Static Discharge • the movement of electrons to relieve a separation in charge

  5. B. Conductors • Conductor • material that allows electrons to move through it easily • e- are loosely held • ex: metals like copper and silver

  6. C. Insulators • Insulator • material that doesn’t allow electrons to move through it easily • e- are tightly held • ex: plastic, wood, rubber, glass

  7. D. Electroscope • Electroscope • instrument that detects the presence of electrical charges • leaves separate when they gain either a + or - charge

  8. II. Electric Current Circuit Potential Difference Current Resistance Ohm’s Law

  9. Potential Difference

  10. B. Potential Difference • Potential Difference (voltage) • difference in electrical potential between two places • large separation of charge creates high voltage • the “push” that causes e- to move from - to + • measured in volts (V)

  11. C. Current • Current • flow of electrons through a conductor • depends on # of e- passing a point in a given time • measured in amperes (A)

  12. Copper - low resistance Tungsten - high resistance D. Resistance • Resistance • opposition to the flow of electrons • electrical energy is converted to thermal energy & light • measured in ohms ()

  13. Resistance • Caused by internal friction in conductor and slows the movement of charges. • A 40 W light bulb is dim and has a higher resistance than a bright 100W light bulb.

  14. https://www.youtube.com/watch?v=KvVTh3ak5dQ • Resistance video

  15. D. Resistance • Resistance depends on… • the conductor • wire thickness • less resistance in thicker wires • wire length • less resistance in shorter wires • temp - less resistance at low temps

  16. E. Ohm’s Law • Ohm’s Law V: potential difference (V) I: current (A) R: resistance () V = I × R • Voltage increases when current increases. • Voltage decreases when resistance increases.

  17. V R I E. Ohm’s Law • A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? WORK: I = (120 V) ÷ (160 ) I = 0.75 A KNOWN/UNKNOWN: R = 160  V = 120 V I = ? EQUATION: I = V ÷ R

  18. Superconductors Some metals have zero resistance when their temperature falls below a certain temperature (critical temperature). The range is from -458º F to -189ºF.

  19. III. Electrical Circuits Circuit components Series circuits Parallel circuits Household circuits

  20. https://www.youtube.com/watch?v=l8JS8BbrVOg • Video • https://www.youtube.com/watch?v=lYZUXV-v71Y

  21. https://www.youtube.com/watch?v=D2monVkCkX4 Circuits

  22. A. Circuit • Circuit • closed path through which electrons can flow

  23. A. Circuit Components A - battery C - light bulb B - switch D - resistor

  24. B. Series Circuits • Series Circuit • current travels in a single path • one break stops the flow of current • current is the same throughout circuit • lights are equal brightness • each device receives a fraction of the total voltage • get dimmer as lights are added

  25. C. Parallel Circuits • Parallel Circuits • current travels in multiple paths • one break doesn’t stop flow • current varies in different branches • takes path of least resistance • “bigger” light would be dimmer • each device receives the total voltage • no change when lights are added

  26. D. Household Circuits • Combination of parallel circuits • too many devices can cause wires to overheat • Safety Features: • fuse - metal melts, breaking circuit • circuit breaker - bimetallic strip bends when hot, breaking circuit

  27. IV. Measuring Electricity Electrical Power Electrical Energy

  28. A. Electrical Power • Electrical Power • rate at which electrical energy is converted to another form of energy P: power (W) I: current (A) V: potential difference (V) P = I × V

  29. A. Electrical Power • A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use? KNOWN/UNKNOWN: I = 0.01 A V = 9 V P = ? EQUATION: P = I · V EQUATION: P = (0.01 A) (9 V) P = 0.09 W P V I

  30. B. Electrical Energy • Electrical Energy • energy use of an appliance depends on power required and time used E: energy (kWh) P: power (kW) t: time (h) E = P × t

  31. B. Electrical Energy • A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day? UNKNOWN/KNOWN: P = 700 W = 0.7 kW t = 10 h E = ? WORK: E = P · t E = (0.7 kW) (10 h) E = 7 kWh EQUATION: E = P · t E t P

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