On August 6, 1945 the Little Boy (One of the Atomic Bombs) 

was set off in Hiroshima. Even though the Little Boy was smaller

 than the Fat Man it had a bigger explosion because it 

was more compact then Fat Man.  

On August 9, 1945 the Fat Man

 (Another type of an Atomic Bomb) was set off

Nagasaki.  It was bigger than the

 little boy but had less of an effect and

 covered less area.