Question

The work function of a metal is 4.0 eV. if the metal is irradiated with radiation of wavelength 200 nm, then the maximum kinetic energy of the photoelectrons would be about

• A. 6.4 × 10^–19 J
• B. 3.5× 10^–19 J
• C. 1.0 × 10^–18 J
• D. 2.0 × 10^–19 J

Answer 1

Answer: (B)

3.5× 10^–19 J

Answer 2

W₀ = 4.0 eV = $\frac{hc}{\lambda_{0}}$

= 4 × 1.6 × 10^–19 J

n = 3 × 10¹⁵ Hz

6.4 × 10^–19 J

Now apply KE = $\frac{hc}{\lambda}$ –$\frac{hc}{\lambda_{0}}$

where given l = 200 nm = 2 × 10^–7 m