Final answer:
Variations in current in a circuit with an LDR are caused by changes in the light intensity from an incandescent lamp, which alters the LDR's resistance and thereby affects the current according to Ohm's Law.
Step-by-step explanation:
To study the variations in current flowing in a circuit containing an LDR (Light-Dependent Resistor) because of a variation in the distance of an incandescent lamp of fixed power used to illuminate the LDR, it's important to understand the relationship between current, resistance, and voltage as described by Ohm's Law. The current I in a circuit is given by the equation I = V/R, where V is the voltage and R is the resistance. Since an incandescent lamp emits light when heated by current, it functions as a resistor whose resistance changes with temperature.
As the distance between the incandescent lamp and the LDR varies, the intensity of light reaching the LDR changes, which in turn alters its resistance. A closer lamp will result in more intense light, decreasing the resistance of the LDR and thus increasing the current through the circuit according to Ohm's Law. Conversely, increasing the distance will result in less intense light, increasing the resistance of the LDR, and therefore decreasing the circuit current. Additionally, power P can be found using P = IV, where I is the current and V the applied voltage.