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Understanding Current and Resistance: Principles of Moving vs. Nonmoving Charge

This article explores the fundamental principles of electric charge, focusing on the differences between moving and nonmoving charges. It explains how charged objects exert electrostatic forces, the role of voltage in circuits, and how current (flow of electrons) is influenced by resistance. You'll learn about circuit components, including voltage sources, resistors, and the significance of controlling current flow. Key concepts like the junction rule and the factors affecting resistance, such as material type, length, cross-sectional area, and temperature, are also discussed.

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Understanding Current and Resistance: Principles of Moving vs. Nonmoving Charge

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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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