JEE MAIN - Physics (2025 - 22nd January Evening Shift - No. 15)
Explanation
Let's break down the problem step by step.
The photoelectric equation is given by:
$$K_{\text{max}} = \frac{hc}{\lambda} - \phi$$
where:
$$K_{\text{max}}$$ is the maximum kinetic energy of the electrons.
$$\frac{hc}{\lambda}$$ is the energy of the incident photon.
$$\phi$$ is the work function of the metal.
For the initial light source of wavelength $$\lambda$$, we know:
$$2 \text{ eV} = \frac{hc}{\lambda} - 1 \text{ eV}$$
Solving for $$\frac{hc}{\lambda}$$ gives:
$$\frac{hc}{\lambda} = 2 \text{ eV} + 1 \text{ eV} = 3 \text{ eV}$$
Now, if the wavelength is halved to $$\frac{\lambda}{2}$$, the photon energy becomes:
$$\frac{hc}{\lambda/2} = \frac{2hc}{\lambda} = 2 \times 3 \text{ eV} = 6 \text{ eV}$$
The maximum kinetic energy for the new wavelength is then:
$$K'_{\text{max}} = 6 \text{ eV} - 1 \text{ eV} = 5 \text{ eV}$$
Therefore, the maximum kinetic energy of the ejected electrons when the surface is illuminated by a light source of wavelength $$\frac{\lambda}{2}$$ is 5 eV.
The correct answer is Option A.
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