The first operation involved in a Carnot cycle is

Temperature remaining constant, the pressure of gas is decreased by $20 \%$. The percentage change in volume

A plane mirror is placed at the bottom of a tank containing a liquid of refractive index ' $\mu$ ', ' $p$ ' is a small object at a height ' $h$ ' above the mirror. An observer ' $O$ ' vertically above ' $p$ ' outside the liquid sees ' $p$ ' and the image in a mirror. The apparent distance between these two will be

A light bulb connected in series with a capacitor and an a.c. source is glowing with a certain brightness. On reducing the capacity of capacitance and frequency of source, the brightness of the lamp (respectively)