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  4. In a photoelectric effect experiment the threshold wavelength of the light is 380 nm. If the wave length of incident light is 260 nm, the maximum kinetic energy of emitted electrons will be: Given E (in eV) = (1237/λ (in nm))

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Q. In a photoelectric effect experiment the threshold wavelength of the light is $380\, nm$. If the wave length of incident light is $260\, nm$, the maximum kinetic energy of emitted electrons will be:
Given E (in eV) = $\frac{1237}{\lambda (in\, nm)}$

JEE MainJEE Main 2019Dual Nature of Radiation and Matter

Solution:

$K_{max } = \frac{hc}{\lambda} - \frac{hc}{\lambda_{0}}$
$ \Rightarrow K_{max } = hc \left(\frac{\lambda_{0} -\lambda}{\lambda\lambda_{0}}\right) $
$ \Rightarrow K_{max } = \left(1237\right) \left(\frac{380 -260}{380 \times260}\right) $
$ = 1.5 \,eV $