Chapter 9: Q9.23P (page 424)
(a) Shallow water is non-dispersive; waves travel at a speed that is proportional to the square root of the depth. In deep water, however, the waves can’t “feel” all the way down to the bottom—they behave as though the depth were proportional to λ. (Actually, the distinction between “shallow” and “deep” itself depends on the wavelength: If the depth is less than λ, the water is “shallow”; if it is substantially greater than λ, the water is “deep.”) Show that the wave velocity of deep water waves is twice the group velocity.
(b) In quantum mechanics, a free particle of mass m traveling in the x direction is described by the wave function
wherep is the momentum, and
Short Answer
(a) It is proved that the wave velocity of deep water waves is twice the group velocityas
(b) The group velocity and the wave velocity is