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Radiation of wavelength λ, is incident on a photocell. The fastest emitted electron has speed v. If the wavelength is changed to (3λ)/4, the speed of the fastest emitted electron will be

Asked in JEE Main 2016 · Speed and kinetic energy of the photoelectrons

• (1) >v(4/3)^1/2
• (2) <v(4/3)^1/2
• (3) =v(4/3)^1/2
• (4) =v(3/4)^1/2

Step-by-step solution

Why the other options are wrong

• (2) comes from gets the inequality the wrong way round; the leftover φ/3 raises the energy above 4/3 K
• (3) comes from treating the work function as zero, so that K∝1/λ
• (4) comes from scaling the speed with the wavelength rather than with the photon energy

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