A lens of power -2.5 D is MCQ with Answer and Explanation

Explanation:
The Doppler Effect is the apparent change in the frequency (and thus pitch) of a wave due to the relative motion between the source and the observer. As the ambulance approaches, sound waves get compressed, increasing the perceived frequency (higher pitch). As it moves away, waves stretch, lowering the frequency.

Explanation:
Fringe width β = λD/d, where λ wavelength, D screen distance, d slit separation. New d' = 2d, new D' = D/2. Thus β' = λ(D/2)/(2d) = λD/(4d) = β/4. Fringe width reduces to one-fourth. Memory tip: 'β ∝ D/d; changes multiply'. This proportional reasoning problem tests wave optics understanding, frequently appearing in competitive exams. Always track how each parameter change affects the result; combine multiplicative factors for net effect. Verify with dimensional analysis: β has length dimension, consistent with λD/d.

Explanation:
F = qvB sinθ, max at θ=90°.