Q179 / 200 · Manipal (MET) 2013 · Physics

If the work function of a potential is 6.875 eV , its threshold wavelength will be (Take $=c=3 \times 10^8 \mathrm{~m} / \mathrm{s}$ )

  • A
    $3600 Å$
  • B
    $2400 Å$
  • Correct answer
    C
    $1800 Å$
  • D
    $1200 Å$

Solution

$W=\frac{h c}{\lambda}$ where $h$ is planck's constant, c is speed of light, $\lambda$ is wavelength $\begin{aligned} & \lambda=\frac{h c}{W}=\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{6.825 \times 1.6 \times 10^{-19}} \\ & \lambda=1800 Å\end{aligned}$

Hence, the correct answer is option: 'C'.

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