Range of former explosion includes energy (6)
I believe the answer is:
extent
'range' is the definition.
(I've seen this in another clue)
'former explosion includes energy' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'explosion' becomes 'tnt' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'includes' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mcn).
'tnt' going around 'e' is 'tent'.
'ex'+'tent'='EXTENT'
'of' is the link.
Can you help me to learn more?
(Other definitions for extent that I've seen before include "Degree - amount - scope" , "Bulk - compass" , "reach?" , "stretch" , "Area something covers" .)