Why does stone lying in the sun get heated up much more than water lying for the same duration of time?

A pond appears to be 2.7 m deep. If the refractive index of water is 4/3, find the actual depth of the pond.

The wave lengths for the light of red and blue colours are nearly 7.8 x 10^-7 m and 4.8 x 10^-7 m respectively.

(i) Which colour has the greater speed in a vacuum?

(ii) Which colour has a greater speed in glass?

A sound wave travelling in water has wavelength 0.4 m. Is this wave audible in air? (The speed of sound in water = 1400 ms^-1).