Threshold frequency for a metal is 10^ 15 Hz. Light of = 4000 Å f… - Vidyadip

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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