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Q3  Given in Fig. 6.11 are examples of some potential energy functions in one dimension. The total energy of the particle is indicated by a cross on the ordinate axis. In each case, specify the regions, if any, in which the particle cannot be found for the given energy. Also, indicate the minimum total energy the particle must have in each case. Think of simple physical contexts for which these potential energy shapes are relevant.

          

 

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Total energy = kinetic energy (KE) + potential energy(PE)

KE > 0 since m and v2 is positive. If KE <0 particles cannot be found. If PE>TE, then KE<0 (now in all graphs check for this condition)

In case 1 kinetic energy is negative for x<a. So at x<a particle cannot be found.

In case 2 for x<a and for x> b kinetic energy is negative. So the particle cannot be found in these regions.

In the third case, the minimum potential energy is when   a<x<b. At this position, the potential energy is negative (- V1).

The kinetic energy, in this case, is given by :

                                                           K.E.\ =\ E\ -\ (-V_1)\ =\ E\ +\ V_1

And the minimum energy of the particle is  - V1.

 

In the fourth case,  the particle will not exist in the states which will have potential energy greater than the total energy.

Thus particles will not exist in    \frac{-b}{2}<x<\frac{b}{2}   and   \frac{-a}{2}<x<\frac{a}{2} .

The minimum energy of the particle will be - V1 as it is the minimum potential energy.

Posted by

Devendra Khairwa

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