Place a Pyrex glass funnel with its mouth-down in a saucepan full of water, in such a way that the stem tube of the funnel is above the water or pointing upward into the air. Rest the edge of the bottom portion of the funnel on a nail or on a coin, so that water can get under it. Place the pan on a stove and heat it till it begins to boil. Where do the bubbles form first? Why? Can you explain how a natural geyser works using this experience?

Explain the following temperature versus time graph:

A steam engine intakes $50 \mathrm{g}$ of steam at $100°\mathrm{C}$ per minute and cools it down to $20°\mathrm{C}$. If latent heat of vaporization of steam is $540 \mathrm{cal} {\mathrm{g}}^{-1}$, then the heat rejected by the steam engine per minute is _____ $\times {10}^3 \mathrm{cal}$

(Given : specific heat capacity of water : $1 \mathrm{cal} {\mathrm{g}}^{-1}{{}^{\circ }\mathrm{C}}^{-1}$)

Heat required to melt $1 \mathrm{g}$ of ice is $80 \mathrm{cal}$. A man melts$60 \mathrm{g}$ of ice by chewing in one minute. His power is______

A thermally insulated cubical box of side length $20 \mathrm{cm}$ and wall thickness $2 \mathrm{cm}$ containing $2 \mathrm{kg}$ of ice is closed on all sides. The mass of ice melted in $10$ hours is (Thermal conductivity of the material of the box $=0.01 {\mathrm{Wm}}^{-1} {\mathrm{K}}^{-1},$ latent heat of ice $=360\times {10}^3 \mathrm{J} {\mathrm{kg}}^{-1}$ and ambient temperature $=40 °\mathrm{C}$)