1 / 81

Definitions

Definitions. Voltage : Electric Potential or Potential Difference (Energy available) V (volts) = Joules/Coulomb One volt = one coulomb of charge gains or loses one joule of energy. Electric Potential. Which is worse, 120 volts or 25,000 volts? It depends….

uta
Download Presentation

Definitions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Definitions • Voltage: Electric Potential or Potential Difference (Energy available) • V (volts) = Joules/Coulomb • One volt = one coulomb of charge gains or loses one joule of energy

  2. Electric Potential • Which is worse, 120 volts • or 25,000 volts? • It depends…. • Energy causes pain… not voltage • Voltage is potentialenergy per charge so 1 volt = 1 Joule of energy per 1 Coulomb of charge

  3. Electric Potential = Voltage • Basic outlet is 120 V • The flow of an outlet is about 20 Coulombs/sec • The energy released in 1 sec would be: Amount of energy to lift 75 gal of water 1 m high!

  4. Electric Potential • Van de Graff generator carries up to 400,000 V! • But, it only flows 10μCoulombs/sec • The energy released in 1 sec would be: Amount of energy to lift 2 cups of water 1 m high

  5. Time to practice Go to pg. 200

  6. Circuits It’s what we see…

  7. Simple Circuits • Whenever you separate + and – charges, you create potential difference. • Potential difference is measured in volts (V) • gives electronsanelectric potential energy • ex. battery, solar panel

  8. Simple Circuits • When separated, - charges will try to flow towards + charges. • This flow is calledcurrent (I) • In a battery, electrons will always flow from the – terminal to the + terminal if they are given a path. • ex. wire

  9. Simple Circuits • You can put a device into this wire that changes the voltage to another form of energy. These devices are called resistors • Resistors can convert electric energy into: • light (ex. lightbulb) • heat (toaster) • motion (motor)

  10. Simple Circuits • Most resistors convert electric potential energy intomore than one type of energy • ex. Light bulbs also give off heat • toaster wires glow (light)

  11. I N S U L A T O R + - + - + - As long as the electrons can move from the negative to the positive, you have a circuit.

  12. Simple Circuits • Electrons only flow when a circuit is a closed loop

  13. Inside a Lightbulb • Each wire of filament connects to a different terminal of the battery • This forces the current to flow through the lightbulbin order to travel in a closed loop

  14. Resistance • All materials give some resistance to flow of charge • 1 exception: superconductors • Insulators have high resistance • ex. rubber, plastic • Conductors have low resistance • ex. metals

  15. Resistance • Amount of resistance depends on: • material • length of wire • thickness of wire (cross-sectional area) • Imagine a straw… it’s easier • to blowthrough when: • shorter • thicker

  16. Calculating Resistance • resistance (Ω = Ohm) • length of wire (m) • cross sectional area of wire (m2) • resistivity depends on material (Ω•m) • R • L • A • ρ

  17. Calculating Resistance semiconductor

  18. ExampleHow much resistance is in the graphite of a 20. cm long pencil if the graphite has a diameter of 4.0 mm? Given: (from table) Unknown:

  19. Examplesolve for R

  20. Time to Practicego to pg. 210start #3

  21. 36 kg = _______ g. 10 3 = kilo (k) 1 kilogram (kg) = 10 3 gram (g) Conversion factors:

  22. Current rate of electric flow • charge (C) • time (s) • current (A) • q • t • I

  23. Current Flow • Conventional Current is the direction positive charges move • Actual electron flow is the other way!

  24. Ohm’s Law • Current depends on two things: • Potential difference (voltage) • Resistance, R • Together, they make Ohm’s Law:

  25. Resistors take Voltage & convert it into a new type of energy Ohm’s Law Voltage pushes charges Current

  26. Ohm’s Law Water Circuit Analogy • Potential Difference (Voltage) • amount of water (pressure)

  27. Voltage would be the water pressure. Think of a geyser as high voltage, and the shower of a low-rent apartment on the fifth floor as low voltage HIGH low

  28. Ohm’s Law Water Circuit Analogy • Switch • turns flow on and off

  29. Ohm’s Law Water Circuit Analogy • Resistance • thickness & length of hose

  30. Ohm’s Law Water Circuit Analogy • Current • rate of flow

  31. Time to Practicego to pg. 210

  32. Electric Shocks • 1 mA • 10 mA • 100 mA = pain = release current = death

  33. Power • Brightness depends on power • Power = rate of energy usage • P = Energy / time • New unit  Watt and so,

  34. Combining Equations twinkle, twinkle…

  35. Power and Energy Energy Equations

  36. Units and Variables Coulombs (C) seconds (s) Volts (V) ohms (Ω) Amperes (A) Joules (J) Watts (W)

  37. Example 1In 3.0 minutes an electric pot delivers 48,000 J of energy to the water inside it. The coffee pot is connected to a standard 120-volt source. What is the resistance of the coffee pot? Given: Want:

  38. Example1pick an equation

  39. The Cost of Electricity Let’s take a close look at the unit: kilowatt-hour • Unit: kW = P • Unit: hr = t Pt = E • kW-hr is a unit of Energy

  40. Example 21 kW-hr costs $0.12:Let’s find the cost of running a 60 W light bulb for 24 hours Given: Unknown:

  41. Example 21 kW-hr costs $0.12:Let’s find the cost of running a 60 W light bulb for 24 hours 1. Let’s solve for energy the lightbulb uses

  42. Example 21 kW-hr costs $0.12:Let’s find the cost of running a 60 W light bulb for 24 hours 2. Let’s solve for cost of the energy the lightbulb uses

  43. Example 2 – Unit Analysis!Let’s find the cost of running a 60 W light bulb for 24 hours Given:

  44. Time to Practice#7DCalculate the cost of cooking a cake go to pg. 211

  45. Warning You are about to learn how to operate the most difficult measuring tool of the year Pay very close attention…

  46. Measuring Resistance • Symbol: Ω • Isolate the resistor from circuit • Place leads on each side • Ohmmeter

  47. Measuring Voltage • Symbol: V • Voltage source must be connected to circuit • Place leads on each side of the source • Voltmeter

  48. Measuring Current • Symbol: A • Need to break open the circuit • Force current through the meter by making the meter part of the circuit • ammeter

  49. Time to PracticeStart the Lab Warm-upRefer to pg. 215- 216 for instructions on how to measure

  50. Measuring voltage: Use the 2V or 200V setting (circled below). If the meter reads “1” go up to 200V, if it reads “0” go down to 2V. Measuring resistance: Use the “Ω” portion of the meter in the “2,000” Ohm setting (circled above). Measuring current Use the 200 mA setting (circled above) with the red lead plugged into “mA.” Time for lab! Go to page 268

More Related