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Current and resistance

Current and resistance. Principles of Physics. Moving vs. Nonmoving Charge. So far, we’ve talked about non-moving charge We know that charged objects : exert an electrostatic force on each other move when the force is unbalanced

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Current and resistance

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  1. Current and resistance Principles of Physics

  2. Moving vs. Nonmoving Charge So far, we’ve talked about non-moving charge We know that charged objects : • exert an electrostatic force on each other • move when the force is unbalanced • gain and lose energy as they move toward and away from other charged objects • Moving toward a like charge → increase in PE • Moving away from like charge→ decrease in PE We also know that a voltage exists between charged objects

  3. Moving vs. Nonmoving Charge • Charged objects are not useful unless moving • They move if there is a voltage Circuit A system in which charged objects move in response to a voltage source Must include: voltage source (battery) closed path for charges to follow (wires) method of controlling rate of flow (resistor)

  4. Current Current (I): flow of electrons (negative charge) • In circuits charge is moving in solid materials (copper wires) • Only electrons can move in solids (Positive charge may flow in liquids or gases)

  5. Current Current/electron flow is calculated by I = Current q = charge (C) t = time (s) Current units: 1 C/s = 1 Ampere = 1 Amp = 1 A I = q t

  6. Simple Circuit Voltage supply (power supply) Resistor Wire - +

  7. Current Electrons flow from the negative side of the voltage supply (the short side) Conventional current flows from the positive side of the voltage supply (the long side) - +

  8. Junction Rule Junction: where multiple wires (paths) meet All current flowing into a junction = all current flowing out of a junction. Current flowing in: 1.5 A + 2.5 A = 4 A 1.5 A 2.5 A 1.0 A Current flowing out: 3.0 A IN = OUT *Always add x to the side with less current 4 A = 3.0 A + x 3.0 A

  9. Controlling Current • When one electron leaves from the negative side of the voltage supply another one enters the positive side • The rate that electrons leave is current • How fast they leave depends on resistance in the circuit

  10. Resistance • A material with high resistance typically causes the electrons to experience more collisions as they move through

  11. RESISTOR

  12. Controlling Current http

  13. Resistance, R, is related to: • Type of material • Some materials have more resistance than others • Length • Electrons will experience more collisions as they travel through the longer resistor • Cross sectional area • Increasing cross sectional area decreases resistance because more electrons can get through at one time • Temperature • In metallic conductors, as temperature increases, resistance increases

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