What is Electrical Resistance

Introduction to Electrical Resistance

  • Definition: Resistance is the opposition to the flow of current, which is the movement of charge (electrons) in a metallic conductor.

Understanding Current

  • Moving Charges: In this context, the moving charges are electrons.

  • Modeling Electrons: Visualize electrons as marbles flowing along a wire, demonstrated with Jenga blocks.

  • Energy Source: Energy is provided to the system by elevating the table (analogous to a battery supplying voltage).

  • Current Measurement: The flow of electrons (current) was measured to take just over six seconds for a quantity to pass a specific point.

    • Current Relation: A longer time indicates smaller current (fewer electrons passing in a given time).

Factors Affecting Resistance

  • Resistance Equation:

    • Resistance (R) = Resistivity (ρ) * Length (L) / Area (A)

    • Resistivity (ρ): A material-specific value influencing resistance.

    • Increasing Resistance:

      • Increasing either resistivity or length will increase resistance.

      • Increasing the cross-sectional area will decrease resistance.

Experimental Testing of Resistance

  • Increasing Resistivity:

    • By adding obstructions (analogous to defects in a material's lattice), the electrons collide, resulting in greater resistance.

    • Time Measurement: The electrons took 11 seconds to pass through the wire due to increased resistivity, decreasing current.

  • Increasing Wire Cross-sectional Area:

    • When the wire's area was increased, the time decreased to three seconds, indicating more room for electron flow.

Length of the Wire and Its Effect

  • Longer Wires: Lengthening the wire leads to more collisions with obstructions, demonstrating increased resistance (examined through time taken).

  • Observation of Collision:

    • Electrons at the back encountered two obstructions, while those at the front flowed unobstructed.

Resistor Demonstration

  • Resistor Functionality: A resistor represents a wire segment with a known amount of resistance.

  • Wider and Narrow Areas: Reducing the width of the wire at one point creates a resistor effect.

  • Time Measurement at Resistor: The electrons took 11 seconds again to pass the narrow area, illustrating restricted flow due to increased resistance.