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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Photoelectric Effect and Wave–Particle Duality

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Photoelectric Effect and Wave–Particle Duality

The electric field associated with a light wave at a point is given...

The electric field associated with a light wave at a point is given by E=(100 Vm−1)sin⁡ ⁣[(3.0×1015 s−1)t]sin⁡ ⁣[(6.0×1015 s−1)t]E = (100 \text{ Vm}^{-1}) \sin\! \left[(3.0 \times 10^{15} \text{ s}^{-1}) t\right] \sin\!\left[(6.0 \times 10^{15} \text{ s}^{-1}) t\right]. When this light is incident on a metal surface with a work function of 2.0 eV,determinethemaximumkineticenergyoftheemittedphotoelectrons.2.0 \text{ eV}, determine the maximum kinetic energy of the emitted photoelectrons.

Options

  1. A5.93 eV5.93 \text{ eV}
  2. B3.93 eV3.93 \text{ eV}
  3. C1.95 eV1.95 \text{ eV}
  4. D35.26 eV35.26 \text{ eV}

Correct answer

B. 3.93 eV3.93 \text{ eV}

Step-by-step solution

The given electric field of the light wave is:

E=100sin⁡(3.0×1015t)sin⁡(6.0×1015t)E = 100 \sin(3.0 \times 10^{15} t) \sin(6.0 \times 10^{15} t)

Using the trigonometric identity 2sin⁡Asin⁡B=cos⁡(A−B)−cos⁡(A+B)2 \sin A \sin B = \cos(A-B) - \cos(A+B), the electric field can be written as:

E=50[cos⁡(3.0×1015t)−cos⁡(9.0×1015t)]E = 50 [\cos(3.0 \times 10^{15} t) - \cos(9.0 \times 10^{15} t)]

This indicates that the light wave is a superposition of two waves with angular frequencies ω1=3.0×1015 s−1\omega_1 = 3.0 \times 10^{15} \text{ s}^{-1} and ω2=9.0×1015 s−1\omega_2 = 9.0 \times 10^{15} \text{ s}^{-1}.

The maximum kinetic energy of the emitted photoelectrons is determined by the photon with the higher frequency, which is ω2=9.0×1015 s−1\omega_2 = 9.0 \times 10^{15} \text{ s}^{-1}.

The energy of this incident photon is:

Ep=hω22π=6.63×10−34×9.0×10152π×1.6×10−19 eVE_p = \dfrac{h \omega_2}{2\pi} = \dfrac{6.63 \times 10^{-34} \times 9.0 \times 10^{15}}{2 \pi \times 1.6 \times 10^{-19}} \text{ eV}

Ep≈59.67×10−1910.05×10−19 eV≈5.93 eVE_p \approx \dfrac{59.67 \times 10^{-19}}{10.05 \times 10^{-19}} \text{ eV} \approx 5.93 \text{ eV}

Using Einstein's photoelectric equation, the maximum kinetic energy is:

K_{\text\max} = E_p - \phi

K_{\text\max} = 5.93 \text{ eV} - 2.0 \text{ eV} = 3.93 \text{ eV}
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