Question

The kinetic energy of most energetic electrons emitted from a metallic surface is doubled when the wavelength l of the incident radiation is changed from 400 nm to 310 nm. The work function of the metal is-

• A. 0.9 eV
• B. 1.7 eV
• C. 2.2 eV
• D. 3.1 eV

Answer 1

Answer: (C)

2.2 eV

Answer 2

K = $\frac { 12400 } { 4000 }$ – f = 3.1 – f

2K = $\frac { 12400 } { 3100 }$ – f = 4 – f

̃ 6.2 – 2f = 4 – f

or 2.2 eV = f

\ f = 2.2 eV