A certain number of spherical drops of a liquid of radius r coalesce to form a single drop of radius R and volume V. If T is the surface tension of the liquid, then

Steam at 100^oC is passed into 20 g of water at 10^oC. When water acquires a temperature of 80^oC, the mass of water present will be
[Take specific heat of water = 1 cal g^{$$-$$1 o}C^$$-$$1 and latent heat of steam = 540 cal g^$$-$$1]

Certain quantity of water cools from 70^oC to 60^oC in the first 5 minutes and to 54^oC in the next 5 minutes. The temperature of the surroundings is

Copper of fixed volume V is drawn into wire of length $$l$$. When this wire is subjected to a constant force F, the extension produced in the wire is $$\Delta $$$$l$$. Which of the following graphs is a straight line ?