How Current Changes with Voltage for a Component
How Current Changes with Voltage for a Component
Understanding Ohm’s Law
- Ohm’s law is essential to understand how current changes with voltage for a component. It states that the current passing through a conductor between two points is directly proportional to the voltage across the two points.
- If a graph of voltage against current (V-I graph) for a component is a straight line that passes the origin, the component obeys Ohm’s law.
Non-Ohmic Conductors
- Some components do not obey Ohm’s law; these are called non-ohmic conductors. These include filament lamps and diodes. Their current-voltage characteristics can be seen on a curving graph.
- A filament lamp exhibits increasing resistance as the temperature increases. This leads to a curved V-I graph.
Diodes
- A diode allows current to flow in one direction only. It has a high resistance in the opposite direction. This results in a non-linear V-I characteristics graph.
- The forward voltage is when the diode is in its low resistance direction, and it is around the point where the current starts to increase rapidly on the graph.
- The reverse voltage is when the diode is in its high resistance direction, making the current near zero on the graph.
Thermistors and Light Dependent Resistors (LDR)
- Both thermistors and LDRs are types of resistors whose resistance changes with external conditions.
- For a non-ohmic thermistor, the resistance decreases as temperature increases. This makes it useful in temperature-sensing circuits.
- For a light-dependent resistor (LDR), the resistance decreases with increasing light intensity. This makes it useful in light-sensing circuits.