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Electric Fields & Currents

Electric Fields & Currents. Electric Fields Think of electric force as establishing a “field” telling particles which way to move and h ow fast Electric “field lines” tell a positive charge which way to move. For example, a positive charge itself has field lines pointing away from it,

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Electric Fields & Currents

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  1. Electric Fields & Currents

  2. Electric Fields • Think of electric force as establishing a “field” telling particles which way to move and how fast • Electric “field lines” tell a positive • charge which way to move. • For example, a positive charge itself • has field lines pointing away from it, • because this is how a positively-charged • “test-particle” would respond if placed • in the vicinity (repulsive force). + Run Away! +

  3. Examples of Electric Fields around Charges

  4. Current • Electric current is simply the flow of charge • Electrons flowing in a wire constitute a current • Measured in Coulombs per second, or Amperes • Amp (A) • refers to amount of charge crossing through cross-sectional area per unit time • Electrons have a charge of –1.610-19 Coulombs • so (negative) one Coulomb is 61018 electrons • one amp is 61018 electrons per second • Note: electrons flow in direction opposite to current, since current is implicitly positive charge flow, but electrons are negative

  5. battery + bulb Circuit in Diagram Form • current • In a closed circuit, current • flows around the loop • electrons flow opposite the • indicated current direction! • (repelled by negative terminal

  6. Current flowing through the • filament makes it glow. • No Loop  No Current  No Light

  7. How much would the current through the battery change if I unscrewed one of the 2 bulbs? • How would the brightness of “A” change if I unscrewed “B”? +  A B Currents Divide and Merge at Junctions

  8. The battery is supplying an equal amount of current to each of the two bulbs. If one of the bulbs is disconnected, the current through the battery will be halved. • Unscrewing “B” would not affect the current through “A” so it will stay the same brightness. Answers

  9. capacitor (formerly known as condenser) is a passive two-terminal electric component used to store energy in an electric field What is one way energy can be stored in a device? Capacitor

  10. What is Ohms Law? • Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points

  11. If the potential difference is 120volts and the resistance is 50 ohms, what is the current? Problem

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