I–V Characteristics
- As the potential difference (voltage) across a component is increased, the current also increases (by Ohm’s law)
- The precise relationship between voltage and current is different for different components and can be shown on an I-V graph:
I-V characteristics for metallic conductor (e.g. resistor) and semiconductor diode
- The I-V graph for a metallic conductor at constant temperature e.g. a resistor, is very simple:
- The current is directly proportional to the potential difference
- This is demonstrated by the straight line graph through the origin
- The I-V graph for a semiconductor diode is slightly different. A diode is used in a circuit to allow current to flow only in a specific direction:
- When the current is in the direction of the arrowhead symbol, this is forward bias. This is shown by the sharp increase in potential difference and current on the right side of the graph
- When the diode is switched around, it does not conduct and is called reverse bias. This is shown by a zero reading of current or potential difference on the left side of the graph
Worked example
The I–V characteristic of two electrical component X and Y are shown.
Which statement is correct?
A. The resistance of X increases as the current increases
B. At 2 V, the resistance of X is half the resistance of Y
C. Y is a semiconductor diode and X is a resistor
D. X is a resistor and Y is a filament lamp
Answer: C
- The I-V graph X is linear
- This means the graph has a constant gradient. I/V and the resistance is therefore also constant (since gradient = 1/R)
- This is the I-V graph for a conductor at constant temperature e.g. a resistor
- The I-V graph Y starts with zero gradient and then the gradient increases rapidly
- This means it has infinite resistance at the start which then decreases rapidly
- This is characters of a device that only has current in one direction e.g a semiconductor diode
- Therefore the answer is C
