Lecture Notes: Understanding V = IR and Current vs. Potential Difference Graphs

Key Equation: V = IR

• V = IR is a fundamental equation in electricity:
  • V: Voltage (Potential Difference)
  • I: Current
  • R: Resistance
• Example Calculations:
  • Given: Current = 4 amps, Resistance = 2 ohms
    • Voltage (V): 4 amps × 2 ohms = 8 volts
  • Given: Voltage = 24 volts, Current = 8 amps
    • Resistance (R): 24 volts ÷ 8 amps = 3 ohms

Relationship Between Voltage, Current, and Resistance

• Proportional Relationship: As long as resistance is constant:
  • Increasing voltage leads to increased current, and vice versa.
• Graph Representation:
  • Current vs. Potential Difference Graph:
    • For circuits with only wires or resistors, the graph is a straight line.
    • Negative part of the graph: Battery attached in reverse, showing negative voltage and current.
  • Slope of the Line:
    • Greater Resistance: Less steep line (e.g., 10 ohm resistor).
    • Lesser Resistance: Steeper line.

Temperature Effects

• Assumption: Temperature is constant.
  • In practice, higher currents can increase the temperature, altering resistance.

Filament Lamps and Diodes

• Filament Lamps:
  • Contain a thin metal filament that heats up to emit light.
  • Increased heat results in increased resistance.
  • Graph shows a curve that becomes less steep as current increases.
• Diodes:
  • Allow current to flow only in one direction.
  • Current flows only with positive potential difference.
  • High resistance in the reverse direction prevents reverse current.

Conclusion

• V = IR captures the relationship between voltage, current, and resistance.
• Graphs illustrate the behavior of circuits under different conditions.
• Understanding the behavior of specific components like filament lamps and diodes is crucial.