First slide

Photo Electric Effect

Question

A surface irradiated with light of wavelength 480 nm gives out electrons with maximum velocity 2 v m/s, the cut off wavelength being 600 nm. The same surface would release electrons with maximum velocity 2 v m/s, if it is irradiated by light of wavelength

Moderate

A

300 nm
B

360nm
C

384 nm
D

400 nm

Solution

${(\frac{1}{2} {mv}^{2})}_{max} = \frac{hc}{480 \times 10^{- 9}} - \frac{hc}{600 \times 10^{- 9}} when 4 {(\frac{1}{2} {mv}^{2})}_{max} = \frac{hc}{λ} - \frac{hc}{600 \times 10^{- 9}} \frac{hc}{λ} - \frac{hc}{600 \times 10^{- 9}} = 4 [\frac{hc}{480 \times 10^{- 9}} - \frac{hc}{600 \times 10^{- 9}}] Solving, we get λ = 300 nm .$

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