9.5 I-V characteristics

Question 1

What does the I-V graph for resistors look like?

Answer 1

The p.d. across a resistor is directly proportional (straight-line graph) to the current in the resistor (V∝I). As a result:
* a resistor obeys Ohm’s law and so can be described as an ohmic conductor
*the resistance in the resistor is constant
The resistor behaves in the same way regardless of the polarity.

Question 2

What does the I-V graph for filament lamps look like?

Answer 2

The p.d. across a filament lamp is not directly proportional (curved graph) to the current in the filament lamp:
*a filament lamp does not obey Ohm’s law, and so can be described as as a non-ohmic component
*the resistance of a filament lamp is not constant
The filament lamp behaves in the same way regardless of the polarity.
The resistance of the filament lamp increases as the p.d. across the filament lamp increases.

Question 3

What does the I-V graph for diodes look like?

Answer 3

Diodes allow current in one particular direction. This means that when p.d.<0, I=0 or a very small value. When p.d.>0, current sharply increases as resistance decreases and p.d. increases, similar to a quadratic graph.

Question 4

What does the I-V graph for thermistors look like?

Answer 4

Similar to filament lamp, except that current increases much more drastically. The graph curves upwards instead of plateauing.