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In a photoelectric setup, monochromatic light of wavelength λ ejects electrons, and the maximum speed of the emitted electrons is v. If the incident wavelength is changed to 5λ/4, the speed of the emitted electrons will be

1. v√(5/4)
2. v√(5/3)
3. less than v√(5/3)
4. greater than v√(5/3)

Correct answer: less than v√(5/3)

Solution

As the wavelength of the incident light increases, the energy of the photons decreases, which in turn reduces the kinetic energy of the emitted electrons. Since the maximum speed of the electrons is directly related to their kinetic energy, a longer wavelength results in a lower maximum speed, confirming that it will be less than v√(5/3).

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