In an experiment on photoelectric emission from a metallic surface,the wavelength of incident light is $2 \times 10^{-7} \ m$ and the stopping potential is $2.5 \ V$. The threshold frequency of the metal (in $Hz$) is approximately (charge of electron $e = 1.6 \times 10^{-19} \ C$,Planck's constant $h = 6.6 \times 10^{-34} \ J \cdot s$):

  • A
    $12 \times 10^{15}$
  • B
    $9 \times 10^{15}$
  • C
    $9 \times 10^{14}$
  • D
    $12 \times 10^{13}$

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