Two spheres of same material and radius r and 2r are heated to same temperature and are kept in identical surroundings, ratio of their rate of loss of heat is

A sphere and a cube both made of copper have equal volumes and are blackened. These are heated to same temperature and are allowed to cool under same surroundings. The ratio of their rates of loss of heat is

A cube and a sphere (both solid) of same mass, same material are heated upto same temperature and then kept in same surrounding. Rate of cooling means rate of fall of temperature

A solid sphere and a hollow sphere of the same material and size are heated to the same temperature and allowed to cool in the same surroundings. If the temperature difference between the surroundings and each sphere is T, then :

A solid sphere and a hollow sphere of same material and size are heated to same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surrounding is T, then