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11. Dual nature of radiation and matter — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics11. Dual nature of radiation and matter1 Mark
MCQ
Threshold frequency for a metal is ${10^{15}}Hz$. Light of $\lambda = 4000{Å}$ falls on its surface. Which of the following statements is correct
  • ✓
    No photoelectric emission takes place
  • B
    Photo-electrons come out with zero speed
  • C
    Photo-electrons come out with $10‌‌^3 m/sec$ speed
  • D
    Photo-electrons come out with $10^5 m/sec$ speed
✓

Answer

Correct option: A.
No photoelectric emission takes place
a
(a) Frequency of light of wavelength $(\lambda = 4000\;{Å})$ is $\nu = \frac{c}{\lambda } = \frac{{3 \times {{10}^8}}}{{4000 \times {{10}^{ - 10}}}} = 0.75 \times {10^{15}}$

which is less than the given threshold frequency. Hence no photoelectric emisssion takes place.

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