Dual Nature of Radiation and Matter

  • Question 1
    CBSEENPH12039408

    Why are infra-red waves often called heat waves? Explain.

    Solution

    Infrared waves produced from hot bodies. Hence, it often called heat waves.

    Question 2
    CBSEENPH12039409

    What do you understand by the statement, 'Electromagnetic waves transport momentum'?

    Solution

    When electromagnetic waves hit the body the mass is lost by the momentum is conserved. i.e., transferred from Electromagnetic waves to the body.

    Question 3
    CBSEENPH12039410

    If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

    Metal Work Function (eV)
    Na 1.92
    K 2.15
    Ca 3.20
    Mo 4.17

    Solution

    A metal will show photoelectric emission in below situation:
    E ≥ work function
    Now according to the relation below:

    E = hv = hcλ (J) = hcλe (eV) = 6.6 x 10-34 x 3 x 108412.5 x 10-9 x 1.6 x 10-19E = 3 ev

    The work function of k and Na are less than the incident energy of the photon. Hence, only potassium (k) and Sodium (Na) will show photoelectric emission.

    Question 4
    CBSEENPH12039594

    The surface of a metal is illuminated with the light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is (hc = 1240 eV nm)

    • 3.09 eV

    • 1.41 eV

    • 151 eV

    • 1.68 eV

    Solution

    B.

    1.41 eV

    hc over straight lambda space equals straight ϕ space plus space left parenthesis KE right parenthesis subscript max
rightwards double arrow space 1240 over 400 space equals space straight ϕ plus space 1.68
rightwards double arrow space straight ϕ space equals space 1.41 space eV

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