Optical Devices : Electronic Devices MCQ Practice Questions & Answers (Bengali)

Electronic DevicesEasyOptical DevicesOptical Absorption Photon Absorption Coefficient

Photons absorbed in the matter are converted to heat. A source emitting n photons/sec of frequency ν is used to convert 1 kg of ice at 0°C to water at 0°C. Then, the time T taken for the conversion:

Increases with increasing n, with ν fixed

Increases with n fixed, ν increasing

Remains constant with n and ν changing such that nν = constant

Increases when the product nν increases

Correct Answer:

Explanation:

The correct answer is C.

Concept: The energy released or absorbed during a phase change is given by E = mL, where m is the mass of the substance and L is the latent heat.

Derivation:

Energy required to convert ice to water: mL = 1000 g × 80 cal/g = 80,000 cal
Total energy delivered by the photon source in time T: E = nT × hν
Setting them equal: nThν = mL
Therefore: T = mL / (nhν)

From this expression:

T ∝ 1/n when ν is constant — so T decreases as n increases (Option 1 is incorrect).
T ∝ 1/ν when n is constant — so T decreases as ν increases (Option 2 is incorrect).
If nν = constant, then T = mL / (h × nν) = constant — T remains unchanged (Option 3 is correct).
If nν increases, T decreases, not increases (Option 4 is incorrect).

Optical Devices in Electronic Devices : Practice MCQ Questions & Answers with Explanations

Optical Devices in Electronic Devices : Practice MCQ Questions & Answers with Explanations