The efficiency of a Carnot engine working between 27°C and 127°C is MCQ with Answer and Explanation

Explanation:
A Wheatstone bridge circuit consists of four arms with resistances P, Q, R, S and a galvanometer in the middle. It is balanced when no current flows through the galvanometer arm. This happens exclusively when the potentials at the two ends of the galvanometer are equal, meaning the potential difference across it is exactly zero (P/Q = R/S).

Explanation:
Ammeter measures current, must be in series so full current flows through it. Low internal resistance to minimize voltage drop. Voltmeter measures potential difference, connected in parallel, high resistance.

Explanation:
Oil immersion increases numerical aperture (NA) by matching refractive indices, improving resolution d = λ/(2NA). Memory tip: 'Higher NA or shorter λ ⇒ better resolution'. Optical instrument concept frequently tested in competitive exams.