Final answer:
A rheostat in a light circuit should be connected in series to adjust light intensity by varying the current flowing through the bulb, thus controlling the brightness.
Step-by-step explanation:
When adding a rheostat to a light circuit to control the light intensity, it should be connected in series with the light bulb.
Connecting it in series allows for the adjustment of the current flowing through the circuit, and consequently, the intensity of the light.
As the resistance of the rheostat is increased, less current flows to the light bulb, dimming it. If the resistance is decreased, more current flows, and the bulb becomes brighter.
This happens because the power supplied to the light bulb is determined by the formula P = IV, where P is the power, I is the current, and V is the voltage. A rheostat effectively controls the current I, as per Ohm's law I = V/R, where R is resistance, by changing its resistance value.