Q.

When a particle is restricted to move along the x-axis between x=0 and x=a, where a is of nanometer dimension, its energy can take only certain specific values. The allowed energies of the particle moving in such a restricted region, correspond to the formation of standing waves with nodes at its ends x=0 and x=a. The wavelength of this standing wave is related to the linear momentum p of the particle according to the de Broglie relation. The energy of the particle of mass m is related to its linear momentum as E=p22m. Thus, the energy of the particle can be denoted by a quantum number n taking values 1,2,3,… (n=1, called the ground state) corresponding to the number of loops in the standing wave.

Use the model described above to answer the following three questions for a particle moving in the line x=0 to x=a. Take h=6.6×10-34J s and e=1.6×10-19C.
 

Q.    If the mass of the particle is m=1.0×10-30kg and a=6.6 nm the energy of the particle in its ground state is closest to        [2009]

1 0.8 meV  
2 8 meV  
3 80 meV  
4 800 meV  

Ans.

(2)

For ground state, n=1

Given, m=1.0×10-30kg,  a=6.6×10-9m

∴  E=n2h28ma2=12×(6.6×10-34)28×1×10-30×(6.6×10-9)2 J

=8 meV