Could they burn 50 units of electricity? (5)
I believe the answer is:
lamps
'electricity?' is the definition.
Although both the answer and definition are nouns, they are not in the same form of the noun.
'could they burn 50 units' is the wordplay.
I cannot really understand how this works, but
'50' could be 'l' (Roman numeral) and 'l' is found in the answer.
'units' could be 'amps' (the amp is a unit of electrical current) and 'amps' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for lamps that I've seen before include "light fittings" , "Lights" , "Devices for giving light" .)