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The matter wave dispersion relation given in equation (6-23) is correct only at low speed and when mass/internal energy is ignored.

(a) Using the relativistically correct relationship among energy, momentum and mass, show that the correct dispersion relation is

=k2c2+m2c42

(b) Show that in the limit of low speed (small p and k) and ignoring mass/internal energy, this expression aggress with that of equation (6-23).

Short Answer

Expert verified

(a) The correct matter wave dispersion relation =k2c2+m2c42 is proved.

(b) The equation (6-23) agrees with correct dispersion relationship at low speed.

Step by step solution

01

Matter Waves

The matter waves are used to relationship between momentum and wavelength of particle. If the wavelength of the particle is high then momentum of particle is low.

02

Proof for correct dispersion relation

(a)

The energy of the particle of matter wave is given as:

E=

Here, is the angular frequency of matter wave

The momentum of the particle of matter wave is given as:

p=k

Here, k is the wave number for matter wave

The relativistically correct relation among energy, momentum and mass is given as:

E2=p2c2+m2c4

Substitute all the values in the above equation.

2=k2c2+m2c422=2k2c2+m2c42=k2c2+m2c42=k2c2+m2c42

Therefore, the correct matter wave dispersion relation is proved.

03

Proof for matter waves at low speed

(b)

The wavelength of the matter wave becomes higher if momentum is low at low speed. The internal energy of the wave is also ignored so the correct dispersion relationship holds good and equation (6-23) agrees with correct dispersion relationship at low speed.

Therefore, the equation (6-23) agrees with correct dispersion relationship at low speed.

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Most popular questions from this chapter

Fusion in the Sun: Without tunnelling. our Sun would fail us. The source of its energy is nuclear fusion. and a crucial step is the fusion of a light-hydrogen nucleus, which is just a proton, and a heavy-hydrogen nucleus. which is of the same charge but twice the mass. When these nuclei get close enough. their short-range attraction via the strong force overcomes their Coulomb repulsion. This allows them to stick together, resulting in a reduced total mass/internal energy and a consequent release of kinetic energy. However, the Sun's temperature is simply too low to ensure that nuclei move fast enough to overcome their repulsion.

a) By equating the average thermal kinetic energy that the nuclei would have when distant,32KBT. and the Coulomb potential energy they would have when 2fm apart, roughly the separation at which they stick, show that a temperature of about 1019K would be needed.

b) The Sun's core is only about 10k. If nuclei can鈥檛 make it "over the top." they must tunnel. Consider the following model, illustrated in the figure: One nucleus is fixed at the origin, while the other approaches from far away with energyE. As rdecreases, the Coulomb potential energy increases, until the separation ris roughly the nuclear radius rnuc. Whereupon the potential energy is Umaxand then quickly drops down into a very deep "hole" as the strong-force attraction takes over. Given then EUmax, the point b, where tunnelling must begin. will be very large compared with rnuc, so we approximate the barrier's width Las simply b. Its height, U0, we approximate by the Coulomb potential evaluated at b2. Finally. for the energy Ewhich fixes b, let us use 432KBT. which is a reasonable limit, given the natural range of speeds in a thermodynamic system.Combining these approximations, show that the exponential factor in the wide-barrier tunnelling probability is

exp[-e24蟺蔚0h4m3kBT]

c)Using the proton mass for , evaluate this factor for a temperature of107K. Then evaluate it at3000K. about that of an incandescent filament or hot flame. and rather high by Earth standards. Discuss the consequences.

For wavelengths greater than about,20cm the dispersion relation for waves on the surface of water is=gk

(a) Calculate the phase and group velocities for a wave ofwavelength.

(b) Will the wave spread as it travels? Justify your answer.

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For wavelengths less than about 1 cm, the dispersion relation for waves on the surface of water is =(/p)k3, whereandare the surface tension and density of water. Given=0.072N/mandp=103kg/m3, calculate the phase and group velocities for a wave of 5mm wavelength.

A method for finding tunneling probability for a barrier that is "wide" but whose height varies in an arbitrary way is the so-called WKB approximation.

T=exp[2122m(U(x)E)dx]

Here U(x) is the height of the arbitrary potential energy barrier.Whicha particle first penetrates at x=0 and finally exits at x=L. Although not entirely rigorous, show that this can be obtained by treating the barrier as a series of rectangular slices, each of width dx (though each is still a "wide" barrier), and by assuming that the probability of tunneling through the total is the product of the probabilities for each slice.

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