Ohm's Law is a fundamental principle in electrical circuits that describes the relationship between voltage (V), current (I), and resistance (R). It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.
Mathematically, Ohm's Law is represented as:
V = I * R
Where:
V = Voltage across the component (in volts, V)
I = Current flowing through the component (in amperes, A)
R = Resistance of the component (in ohms, Ω)
Now, let's see how Ohm's Law applies to the behavior of photoresistors and photodiodes:
Photoresistors:
Photoresistors, also known as light-dependent resistors or LDRs, are passive electronic components whose resistance changes with varying light levels. They have a semiconductor material that exhibits photoconductivity, meaning their resistance decreases as light intensity increases.
In the dark or low light conditions, the photoresistor's resistance is high. As more light falls on it, the resistance decreases. The relationship between the resistance (R) of the photoresistor and the current (I) passing through it can be approximately represented by Ohm's Law:
I = V / R
Since the resistance (R) changes with the light intensity, the current (I) through the photoresistor will also change accordingly.
Photodiodes:
Photodiodes are semiconductor devices that convert light into electrical current. They operate in reverse bias, meaning they are designed to have a small, constant voltage applied across them in the opposite direction to their conducting direction.
The current through a photodiode (I) is directly proportional to the light intensity (illumination) falling on the diode. This relationship can be expressed as:
I = Is * exp(qV / (nkT)) - 1
Where:
Is = Reverse saturation current
q = Electron charge
V = Voltage across the photodiode
n = Ideality factor
k = Boltzmann's constant
T = Absolute temperature in Kelvin
This equation describes the current-voltage (I-V) characteristic of a photodiode, and it's based on the diode's intrinsic properties and the light intensity affecting it.
In summary, Ohm's Law doesn't directly apply to photodiodes as it does to passive resistive components, but it is essential in understanding the current-voltage relationship of other components in electrical circuits, including the behavior of photoresistors when used in conjunction with appropriate voltage sources. For photodiodes, their behavior is more complex and involves other diode-related equations to describe their performance under illumination.