A-bombs are the original nuclear bomb, and use fission of big atoms (hence "atomic bomb") to generate the explosion. These are generally much lower yield (up to a few hundred kilotons, maybe 10-20x the size of Hiroshima).
But shortly after inventing the A-bomb, scientists worked out you could generate exponentially more bang by using an A-bomb as a kind of trigger to set off fusion in Hydrogen, like what our star runs off. This is why H(ydrogen)-bombs are also known as "thermonuclear" weapons, because they use the heat generated by the triggering A-bomb to start fusion. H-bombs are way larger, the largest detonated was Tsar Bomba, 50 megatons! (50,000 kilotons). This is about 3,000 times more powerful than the Hiroshima bomb.
So in short, A-bombs are smaller and use fission of heavy elements to make the bang. H-bombs are much more powerful, and use an A-bomb "trigger" to create fusion in a hydrogen fuel source.
ThankYouPhysicist t1_iy7ot2m wrote
Reply to ELI5: What is the difference between an atomic bomb and an "H" bomb? by astarredbard
A-bombs are the original nuclear bomb, and use fission of big atoms (hence "atomic bomb") to generate the explosion. These are generally much lower yield (up to a few hundred kilotons, maybe 10-20x the size of Hiroshima).
But shortly after inventing the A-bomb, scientists worked out you could generate exponentially more bang by using an A-bomb as a kind of trigger to set off fusion in Hydrogen, like what our star runs off. This is why H(ydrogen)-bombs are also known as "thermonuclear" weapons, because they use the heat generated by the triggering A-bomb to start fusion. H-bombs are way larger, the largest detonated was Tsar Bomba, 50 megatons! (50,000 kilotons). This is about 3,000 times more powerful than the Hiroshima bomb.
So in short, A-bombs are smaller and use fission of heavy elements to make the bang. H-bombs are much more powerful, and use an A-bomb "trigger" to create fusion in a hydrogen fuel source.