Why does the bottom of a lake not freeze in severe winter even when the surface is all frozen?

Photoelectric effect supports quantum nature of light because (a) there is a minimum frequency of light below which no photo electrons are emitted (b) the maximum kinetic energy of photo electrons depends only on the frequency of light and not on its intensity (c ) even when the metal surface is faintly illuminated, the photo electrons leave the surface immediately (d) electric charge of the photo electrons is quantised

Why do marine animals live deep inside of lake when the surface of the lake freezes?

A ceiling fan has a diameter (of the circle through the outer edges of the three blades) of 120 cm and rpm 1500 at full speed.Consider a particle of mass 1 g sticking at the outer end of a blade. How much force does it experience when the fan runs at full speed? who exerts this force on the particle? How much force does the particle exert on the blade along its surface?

An air bubble doubles in radius on rising from the bottom of a lake to its surface. If the atmospheric pressure is equal to that of a column of water of height H, the depth of lake is

Find the force exerted by the water on a 2m^2 plane surface of a large stone placed at the bottom of a sea 500 m deep. Does the force depend on the orientation of the surface? Neglect the size of the stone in comparison to the depth of the sea.

Why do astronauts have to wear protective suits when they are on the surface of moon?

Why does a stone sink when placed on the surface of water?

When the size of a soap bubble is increased by pushing more air in it, the surface area increases. Does it mean that the average separation between the surface molecules is increased?