Concepts Of Physics MCQ Edition [Volume 2]PhysicsPhotoelectric Effect and Wave–Particle Duality
Determine the maximum magnitude of the linear momentum of a photoelectron emitted when light of wavelength 400 nm is incident on a metal having a work function of 2.5 eV .
Options
- A8.4 10⁻²⁵ kg m/s
- B9.5 10⁻²⁵ kg m/s
- C4.2 10⁻²⁵ kg m/s
- D2.1 10⁻²⁵ kg m/s
Correct answer
C. 4.2 10⁻²⁵ kg m/s
Step-by-step solution
The energy of the incident photon is given by: E = hc = 6.63 10⁻³⁴ 3 10^8 400 10⁻⁹ J = 4.97 10⁻¹⁹ J The work function of the metal in Joules is: = 2.5 eV = 2.5 1.6 10⁻¹⁹ J = 4.0 10⁻¹⁹ J Using Einstein's photoelectric equation, the maximum kinetic energy of the emitted photoelectron is: K_ max = E - = 4.97 10⁻¹⁹ J - 4.0 10⁻¹⁹ J = 0.97 10⁻¹⁹ J The maximum magnitude of the linear momentum is related to the maximum kinetic energy by: p_ max = 2 m_e K_ max Substituting the mass of an electron m_e = 9.1 10⁻³¹ kg : p_ max