A maiden encountered with hesitation — one sitting in the physics lab? (7)
I believe the answer is:
ammeter
'one sitting in the physics lab?' is the definition.
(an ammeter measures electrical current)
'a maiden encountered with hesitation' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'with' means one lot of letters go next to another.
'hesitation' becomes 'er' (sound used when hesitating).
'a'+'m'+'met'+'er'='AMMETER'
(Other definitions for ammeter that I've seen before include "Measurer of current flow" , "Electric current measurer" , "Device measuring electric current" , "Instrument that measures electric current." , "Instrument measuring electrical current" .)