Which of the following is an example of convection?
a a hot object transferring heat to a cooler one
b the rays of the sun warming the earth
c a hot oven warming the air around it
d hot air rising and cooler air falling

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.