An capacitor C, a variable resistor R and a bulb B are connected in series to the ac mains in circuits as shown if Fig. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance T to be the same, (ii) the resistance R to be the same, (ii) the resistance R is increased keeping the same capacitance.

Explanation

(i) On introducing a dielectric slab between the plates of capacitor, the reactance of capacitor
`(X_(C ) = (1)/(omega C))` will decrease resulting in the increase of current in the circuit. Due to it, the bulb will glow brighter (ii) On increasing resistance R, the effective resistance of circuit increase. Due to it, the current in the circuit decrease. Therefore, the glow of bulb will decrease.