TS EAMCET · Physics · Dual Nature of Matter
A cobalt ( \(\mathrm{Co})\) plate is placed at a distance of \(1 \mathrm{~m}\) from a point source of power \(1 \mathrm{~W}\). Assume a circular area of the plate of radius, \(r=1 \mathrm{~A}\) is exposed to the radiation and ejects photo electrons. The light energy is considered to be spread uniformly and the work function of cobalt is \(5 \mathrm{eV}\). The minimum time the target should be exposed to the light source to eject a photoelectron (Assuming no reflection losses) is
- A \(320 \mathrm{~s}\)
- B \(450 \mathrm{~s}\)
- C \(860 \mathrm{~s}\)
- D \(100 \mathrm{~s}\)
Answer & Solution
Correct Answer
(A) \(320 \mathrm{~s}\)
Step-by-step Solution
Detailed explanation
Given, source power, \(P=1 \mathrm{~W}\) Intensity of light source at a distance of \(1 \mathrm{~m}\) is given by \[ I=\frac{P}{4 \pi r^2}=\frac{1}{4 \pi .1^2}=\frac{1}{4 \pi} \mathrm{W} / \mathrm{m}^2 \] Power absorbed by the circular plates of radius \(1 Å\) is; \(P=I \times\)…
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