I took a quiz where i got two answers wrong and i want to know what the correct answer is and why.

Q1) In a material where both phonons and electrons contribute to the thermal conductivity, the thermal conductivity is always equal to the sum of the individual conductivities when:

a) the phonons are excited by electrons

b) the electrons are excited by phonons

c) the excitation of phonons and electrons are not related

In the book i use in the course i can find that the conductivity do add up, but the book never states why.

Q2) Assume low temperature and constant phonon scattering time in an insulator. When the bulk modulus increase:

a) less phonons are excited and participate in heat conduction b) more phonons are excited and participate in heat conduction c) no answer text provided

For Q2 i know that increased bulk modulus increase the Debye temperature which then leeds to less heat conduction, but i am not sure if it leads to less phonons excited.


1 Answer 1


Hello the correct answer for Q1 is c), you can find the explanation in

this picture


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.