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Aim: How can we explain electric current and resistance?

Aim: How can we explain electric current and resistance?. Do Now: Two charged plates are connected by a wire conductor. What will happen?. +. -. Electron Flow. Current flows from negative to positive. +. -. Electric Current.

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Aim: How can we explain electric current and resistance?

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  1. Aim: How can we explain electric current and resistance? Do Now: Two charged plates are connected by a wire conductor. What will happen? + -

  2. Electron Flow • Current flows from negative to positive + -

  3. Electric Current • The “flow of charge” – the amount of charge that passes a single point in a period of time

  4. Units = Ampere André Marie Ampère 1775 - 1836

  5. A current of 2.0 A is flowing in a circuit. How much charge passes a given point in the circuit in 30 seconds? I = Δq t 2.0 A = Δq 30 s (2.0 A)(30 s) = Δq 60 C = Δq

  6. 5 electrons pass a given point in 1 x 10-18 s. What is the current?

  7. Resistance A measure of how easy or difficult it is for current to flow

  8. Ohm’s Law Units = ohm (represented as Ω) Georg Simon Ohm 1787-1854

  9. A potential of 120 V draws 15 A of current. What is the resistance? A transistor radio of 0.2 A of current is operated by a 9 V battery. What is the resistance?

  10. When solving for other expressions, here’s the electrician’s trick: R = V V = IR I R I =

  11. 75 V flows through a 15 Ω resistor. What is the current? A 60 Ω resistor allows 0.4 A of current to flow. What is the voltage?

  12. What is the potential difference across a 2.0 Ω resistor that draws 2 C of charge per second?

  13. Graph of V vs. I Voltage (volts) Slope is RESISTANCE Current (amps)

  14. Resistance Increases when: • Length of conductor increases/decreases • Cross sectional area of conductor increases/decreases • Temperature of metal conductor increases • Temperature of non-metal conductor decreases Area length

  15. Resistance of Conducting Wire • R = Resistance (Ω) • ρ = Resistivity (Ω•m) • L = Length (m) • A = Cross Sectional Area (m2)

  16. Resistivity

  17. Calculate the resistance of a 2.0-m long Aluminum wire with a cross sectional area of 1.5 x 10-3 m2. R = ρL A R = (2.82 x 10-8Ω•m)(2.0 m) (1.5 x 10-3 m2) R = 3.8 x 10-5Ω

  18. Calculate the resistance of a 5.0-m long Nichrome wire with a radius of 7.5 x 10-6 m. A = πr2 A = π(7.5 x 10-6 m)2 A = 1.77 x 10-10 m2

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