Where should an LDR be placed in a potential divider to sense light?

An LDR, or Light Dependent Resistor, is used in a potential divider circuit to create a varying voltage output that changes in response to varying light levels. The correct placement of the LDR in the circuit is important to ensure that it effectively senses light.

When the LDR is placed in the R1 position, it acts as the top resistor in the divider. In this configuration, the resistance of the LDR decreases when light levels increase, which in turn causes the output voltage across the other resistor in the divider (R2) to change. This behavior allows for a clear relationship between light intensity and the voltage output, which can be measured and utilized in various applications, such as controlling lights or triggering alarms based on ambient light.

Placement in R2 would not provide a direct correlation between light levels and the output voltage, as the LDR's function would be impaired and would not effectively modulate the voltage based on light conditions. Similarly, positioning the LDR in parallel with the power supply or between the output voltage and ground would disrupt the intended operation of the potential divider and result in inconsistent and unreliable output voltages. Thus, the optimal placement for an LDR in a potential divider for sensing light is indeed in R1.