Bring into active operation a specialist with no power (5)

I believe the answer is:

exert

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'bring into active operation a' is the definition.
I can't tell whether this defines the answer.

'specialist with no power' is the wordplay.
'specialist' becomes 'expert' (a specialist is an expert in a field).
'with no' suggests deleting specific letters.
'power' becomes 'p' (symbol in physics).
'expert' with 'p' removed is 'EXERT'.

Can you help me to learn more?

(Other definitions for exert that I've seen before include "Bring to bear, perhaps influence" , "Strain" , "Wield - apply" , "Apply (force)" , "Strive" .)

I've seen this clue in The Irish Times.

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