MCQEasyJEE 2024Photoelectric Effect

JEE Physics 2024 Question with Solution

UV light of 4.13eV4.13 \, \text{eV} is incident on a photosensitive metal surface having a work function of 3.13eV3.13 \, \text{eV}. The maximum kinetic energy of the ejected photoelectrons will be:

  • A

    4.13eV4.13 \, \text{eV}

  • B

    1eV1 \, \text{eV}

  • C

    3.13eV3.13 \, \text{eV}

  • D

    7.26eV7.26 \, \text{eV}

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Energy of incident UV light is 4.13eV4.13 \, \text{eV} and work function of the metal is 3.13eV3.13 \, \text{eV}.

Find: The maximum kinetic energy of the ejected photoelectrons.

Using Einstein's photoelectric equation:

Kmax=hνϕK_{\text{max}} = h\nu - \phi

Substituting the given values:

Kmax=4.13eV3.13eVK_{\text{max}} = 4.13 \, \text{eV} - 3.13 \, \text{eV} Kmax=1eVK_{\text{max}} = 1 \, \text{eV}

Therefore, the maximum kinetic energy of the ejected photoelectrons is 1eV1 \, \text{eV}. The correct option is B.

Direct Energy Difference

Given: Incident photon energy is 4.13eV4.13 \, \text{eV} and work function is 3.13eV3.13 \, \text{eV}.

Find: Maximum kinetic energy.

In the photoelectric effect, the emitted electron gets the leftover energy after overcoming the work function. So subtract the work function from the incident photon energy:

K.E.=4.13eV3.13eV=1eVK.E. = 4.13 \, \text{eV} - 3.13 \, \text{eV} = 1 \, \text{eV}

Therefore, the correct option is B.

Common mistakes

  • Using the incident photon energy itself as the kinetic energy is incorrect because part of that energy is first used to overcome the work function. Always subtract ϕ\phi from hνh\nu.

  • Taking the work function as the answer is incorrect because 3.13eV3.13 \, \text{eV} is the minimum energy needed for emission, not the kinetic energy of the emitted electron.

  • Adding hνh\nu and ϕ\phi is incorrect because the photoelectric equation is Kmax=hνϕK_{\text{max}} = h\nu - \phi, not a sum. The work function is an energy cost, not an extra gain.

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