The circuit diagram shown includes a battery, a light-dependent resistor (LDR) and a buzzer - Junior Cycle Science - Question c - 2015

When the LDR is covered, it is no longer exposed to light. This results in an increase in the resistance of the LDR.

As the resistance of the LDR increases, according to Ohm's law, the current flowing through the circuit decreases. The relationship can be expressed as:

$V = I imes R$

where V is the voltage, I is the current, and R is the resistance.

Since the resistance increases, for a constant voltage provided by the battery, the current must decrease. As the current flowing through the buzzer decreases, it produces a fainter sound, leading to the observation that the noise from the buzzer becomes softer.