The radius of an air bubble is increasing at the rate of 
. At what rate is the volume of the bubble increasing when the radius is 1 cm?
As, the air bubble is in the shape of a sphere.
Therefore, V be the volume of the sphere, then
Therefore, Rate of change of volume (V) with respect to time (t) is given by,
…….. by chain rule
It is given that
when, r = 1cm
Then, 
Therefore, the rate is the volume of the bubble increasing when the radius is 1 cm is 2πcm3/s.
14