Current-Voltage Characteristics

• What does Ohm's law state about current and potential difference?

  Current is proportional to potential difference

  
• What does constant temperature imply in Ohm's law?

  It implies constant resistance
• How is Ohm's law represented mathematically?

  V = IR

  
• How can the relationship between potential difference and current be investigated?

  • Use a circuit with a fixed resistor
  • Adjust resistance on a variable resistor
  • Measure current and potential difference

  
• What type of graph is produced when measuring current with potential difference through a fixed resistor?

  A straight line graph

  
• How can resistance be calculated from the graph of current against potential difference?

  Resistance R = 1 ÷ gradient of the graph

  
• When does an electrical component obey Ohm's law?

  If its graph is a straight line through the origin

  
• Does a resistor obey Ohm's law?

  Yes, a resistor obeys Ohm's law
• Does a filament lamp obey Ohm's law?

  No, a filament lamp does not obey Ohm's law
• Under what condition do metal wires obey Ohm's law?

  If the current isn't large enough to increase temperature
• What happens to the current as the potential difference across a component is increased?

  • Current increases according to Ohm's law
  • Relationship varies for different components

  
• What does the I-V graph look like for an ohmic conductor?

  A straight line through the origin

  
• How does the I-V graph for a semiconductor diode differ from that of an ohmic conductor?

  It has a horizontal line that goes sharply upwards
• What does the I-V graph for a filament lamp look like?

  It has an 'S' shaped curve

  
• Why does the current in a filament lamp increase at a slower rate than potential difference?

  Temperature increases resistance as current rises

  
• When does a filament lamp obey Ohm's law?

  For small voltages
• What are the characteristics of the I-V graph for a semiconductor diode?

  • Forward bias: current flows in one direction
  • Sharp increase in potential difference and current
  • Reverse bias: no current flows

  
• What does a linear I-V graph indicate about a component's resistance?

  Resistance is constant

  
• What does a graph starting with zero gradient indicate about a component?

  It has infinite resistance at the start

  
• What should students be confident in regarding I-V characteristics for different components?

  • Drawing I-V characteristics from memory
  • Recognizing different component behaviors