Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

4 x 10¹⁵ Hz

5 x 10¹⁵ Hz

1.6 x10¹⁵ Hz

2.5 x 10¹⁵ Hz

Solution

1.6 x10¹⁵ Hz

Energy released from emission of electron
E = (-3.4)-(-13.6) = 10.2 eV
From photo electric equation work function
$straight ϕ space equals space straight E space minus eV space equals space hv straight v space equals space fraction numerator straight E minus eV over denominator straight h end fraction space equals fraction numerator left parenthesis 10.2 minus 3.57 space right parenthesis straight e over denominator 6.67 space straight x space 10 to the power of negative 34 end exponent end fraction straight v equals space fraction numerator 6.63 space straight x space 1.6 space straight x space 10 to the power of negative 19 end exponent over denominator 6.67 space straight x space 10 to the power of negative 34 end exponent end fraction space equals space 1.6 space straight x space 10 to the power of 15 space Hz$

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