Question

Work function of nickel is 5.01 eV. When ultraviolet radiation of wavelength 2000 $\mathring{A}$ is incident on electrons are emitted. What will be the maximum velocity of emitted electrons?

• A. $ 3 \times 10^8 \, ms^{ - 1} $
• B. $ 6.46 \times 10^5 \, ms^{ - 1} $
• C. $ 10.36 \times 10^5 \, ms^{ - 1} $
• D. $ 8.54 \times 10^6 \, ms^{ - 1} $

Answer 1

Answer: (B)

Energy corresponding to 2000 $ \mathring{ A} $
E = $ \frac{ 12375 }{ \lambda } = \frac{ 12375 }{ 2000 } e V = 6.2 e V $
Maximum kinetic energy
K = hv $ - h v_0 $
K = E - W
= $ ( 6.2 - 5.01 ) e V = 1.19 \,e V $
Now $ \frac{ 1}{ 2} \times 9. 1 \times 10^{ - 31 } \times V_{ max}^2 = 1.19 \times 1.6 \times 10^{ - 19 } $
or $ v_{ max}^2 = \frac{ 1.19 \times 1.6 \times 10^{ - 19 } \times 2 }{ 9.1 \times 10^{ - 31 }} $
or $ v_{ max}^2 = 0.418 \times 10^{ 12} = 4.18 \times 10^{ 10 } $
or $ v_{ max} = 6.46 \times 10^5 \, m/s $