1 / 9

Recap of main ideas last two days:

Recap of main ideas last two days:. Voltage = change in potential energy per charge Unit: 1 volt = 1 joule/coulomb. Current = rate of charge flow Unit: 1 ampere = 1 coulomb/second.

lenci
Download Presentation

Recap of main ideas last two days:

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. Recap of main ideas last two days: Voltage = change in potential energy per charge Unit: 1 volt = 1 joule/coulomb Current = rate of charge flow Unit: 1 ampere = 1 coulomb/second

  2. Georg Ohm (1789 - 1854) came up with the fact that for most materials, the current through the material is proportional to the voltage across the material, at least for some range of voltages. The proportionality constant is known as Resistance (R) . The equation that is commonly referred to as Ohm’s law is generally written: The Unit of resistance is appropriately called an Ohm. The symbol for the Ohm is W. Quick Question: Why don’t we use the letter O for Ohms?

  3. resistivity L length resistance cross section area A Two factors which determine resistance of an object: • The material’s “resistivity” (r)(good conductors have low resistivity, insulators have high resistivity) • The size and shape of the object (longer, narrower paths have higher resistance) These two factors establish the following relationship:

  4. L d I. 2L d II. 2L Remember: 2d III. L 2d IV. Example question: The four resistors to the right are all made of the same material, and have dimensions as shown. Put them in order from lowest to highest resistance. Smaller L, smaller R Bigger A, smaller R

  5. L d I. 2L d II. 2L Remember: 2d III. L 2d IV. Example question: Put them in order from lowest to highest resistance. Answer: Least R: IV. (small L, big A) 2nd R: III. (A = pr2, bigger factor) 3rd R: I. Most R: II. (big L, small A) Smaller L, smaller R Bigger A, smaller R

  6. And now back to Ohm’s Law... Example Problem: A 1.0 m long wire is connected to a 12 volt battery. 20 coulombs of charge flows through it in 10. seconds. A) What is the current in the wire? I = Q/t I = 20 C/10 s = 2 C/s = 2 A

  7. And now back to Ohm’s Law... Example Problem: A 1.0 m long wire is connected to a 12 volt battery. 20 coulombs of charge flows through it in 10. seconds. B) What is the resistance of the wire? V = IR R = V/I R = 12 V / 2 A R = 6 W

  8. And now back to Ohm’s Law... Example Problem: A 1.0 m long wire is connected to a 12 volt battery. 20 coulombs of charge flows through it in 10. seconds. C) What would the resistance of the wire be if it were 2.5 m long? R is proportional to L L = 2.5 Lo R = 2.5 Ro R = 2.5 x (6W) = 15 W

  9. Tomorrow… What do you get when you multiply Voltage x Current? Answer: Think definitions: Voltage = energy/charge Current = charge/time P = VI

More Related