2.1.6 I–V Graphs

• 1. I Graph

  A graph that plots voltage (V) on the vertical axis and current (I) on the horizontal axis, showing how voltage and current are related for various electrical components
• Ohm’s Law

  Formula: V=I×R, where V is voltage (Volts), I is current (Amperes), and R is resistance (Ohms)
• Equation for Resistance

  R=V/I
• Example Graph

  • A graph with voltage on the y-axis and current on the x-axis; if the graph is a straight line, the resistor obeys Ohm's Law, and the resistance is constant
• Filament Lamp Graph Characteristics

  • Shape: Curved line that starts at the origin and bends upwards
  • At low voltages, resistance is relatively constant; as voltage increases, resistance increases, resulting in a non-linear relationship
• Diode Graph Characteristics

  • Shape: Shows very low current below a certain threshold; once the threshold is reached, current increases rapidly with a small increase in voltage
  • Allows current to flow in one direction (forward bias) once the forward voltage exceeds a certain level
• Thermistors and LDRs

  • Thermistors: Resistance changes with temperature, resulting in a non-linear V-I graph
  • LDRs: Resistance decreases as light intensity increases, affecting the V-I relationship
• Constructing V-I Graphs

  1. Set up the circuit

  2. Collect data

  3. Plot the graph

  4. Analyze the graph
• Set Up the Circuit

  Connect the component in series with a variable power supply and measuring instruments
• Collect Data

  Vary the voltage and measure the corresponding current; record values in a table
• Plot the Graph

  Plot voltage on the y-axis and current on the x-axis; draw the best-fit line or curve
• Analyze the Graph

  Check if the graph is a straight line for Ohmic components; analyze the curve for non-Ohmic components
• Practical Applications

  • Circuit design
  • Component selection
  • Troubleshooting
• Ohmic Resistors

  Have a linear V-I relationship; the graph is a straight line with slope equal to resistance
• Non-Ohmic Components


  Show non-linear V-I relationships; analyze their curves to understand their behavior
• 1. I Characteristics

  Crucial for predicting and analyzing component behavior in electrical circuits