Solved: Calculate for free electrons with average kinetic

Chapter 42, Problem 22E

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QUESTION:

Calculate \(v_{\mathrm{rms}}\) for free electrons with average kinetic energy \(\frac{3}{2} k T\) at a temperature of 300 K. How does your result compare to the speed of an electron with a kinetic energy equal to the Fermi energy of copper, calculated in Example 42.7? Why is there such a difference between these speeds?

Text Transcription:

v_rms

3/2 kT

Questions & Answers

QUESTION:

Calculate \(v_{\mathrm{rms}}\) for free electrons with average kinetic energy \(\frac{3}{2} k T\) at a temperature of 300 K. How does your result compare to the speed of an electron with a kinetic energy equal to the Fermi energy of copper, calculated in Example 42.7? Why is there such a difference between these speeds?

Text Transcription:

v_rms

3/2 kT

ANSWER:

Introduction

We have to first calculate the speed of the electrons in given temperature. Then we have to compare the speed with the speed of the electron at the fermi energy level.

Step 1

The average kinetic energy of the electrons at temperature  is given by

Here we have

 and

Hence the average kinetic energy of the electron is

Now the kinetic energy is also given by

Hence the rms speed of the free electron at the 300 K is m/s.

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