Q. Why do we perspire on a hot day ?
A. The human body is physiologically conditioned to maintain uniform temperature. When the heat produced in the body becomes excessive and is not dissipated properly, the sweat glands inside the body are stimulated to secrete sweat. Therefore, we perspire on a hot day. However, when sweat evaporates from the body, it produces a cooling effect.
Q. Why does a housewife blacken the bottom of the ‘degchi’ used in the kitchen ?
A. The blackened surface absorbs more heat as compared to a polished surface. That is why blackened ‘degchi’ is used.
Q. Why does a coil lying at the bottom of a can filled with water seem to be at lesser distance below the water level than it actually is ?
Why does a swimming pool appear less deep than it really is ?
A. This is due to the phenomenon of refraction of light. The rays of light coming from the bottom of the pool (or from the coil lying at the bottom of the can) travel from water to air. As the rays pass from denser (water) to rarer (air) medium, they bend away from the normal. When the rays are produced back, they form an image of the coil (bottom of the pool) at a point which is a little above the real position. Therefore, the coil appears to be slightly raised and the pool appears to be less deep than it really is.