# griffiths

7. ### Quantum Mechanics: Expectation values (Griffiths)

1. Homework Statement A few questions: Q1) How does 1.29 flow to 1.30 and 1.31? How was the integral-by-parts done? Q2) The author states that <v> = d<x>/dt represents the expectation value of velocity. What does this actually mean? I tried to rationalise that d<x>/dt represented the...
8. ### Proving that torque is m X B

1. Homework Statement Starting from the Lorentz force law, in the form of Fmag = ∫ I (d× B), show that the torque on any steady current distribution (not just a square loop) in a uniform field B is m × B. 2. Homework Equations I looked at the solution I found in this thread here, but I don't...
9. ### Classical Purcell to Jackson?

I heard that Griffith's Electrodynamics is at a similar level of Purcell's book on electricity; is it fine if someone goes into a graduate level electrodynamics book right after Purcell?
10. ### Find the electric field of a uniformly polarized sphere

1. Homework Statement We want to calculate the field of a uniformly polarized sphere of radius=R 2. Homework Equations V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau' 3. The Attempt at a Solution i)I know that \sigma_{b} =...
11. ### How to find the charge density given by a Tricky Potential?

1. Homework Statement I am trying to solve Problem 2.45 in Electrodynamics by Griffiths, however, my answers were different from those in the book, I am suspect I got a missing step but I could not find it, so here is the Given Problem Find the charge density \rho given by a potential...
12. ### Self-studying QM?

Whole my life I have been interested in Quantum Physics. I have a bachelor degree in IT. I did not finish my studies. I have always been quite sloppy in studying in school. As a result, my mathematics skills are terrible. I often get pointed out on this forum that I better start with the...
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### Is Biot Savart Law for a charged particle wrong?

Well, I am a bit confused. Griffiths himself writes in his book "Introduction to Electrodynamics" at one point in his book that this law is "simply wrong". In a footnote, he writes that it was wrong in principle wheras it is true for non-relativistic speeds, and later on in his book, he goes on...
14. ### Quantum Griffiths' revolutions in 20th century physics

hello all Prior to my studies in QM I would need a brief intro to quantum physics. I know there are lot of books on modern physics that cover these topics, but really like Griffiths' style, and my QM textbook is precisely his QM book. So, my question is if "revolutions in 20th century physics"...
15. ### Problem 2.4 Griffiths E&M 3rd ed -- E-field above a square loop

1. Homework Statement The problem states, "Find the electric field a distance z above the center of a square loop (sides of length a) carrying a uniform line charge λ. " The hint says to use the result of example 2.1. Example 2.1 is a similar problem, but instead of a square loop you are...
16. ### Shankar, Feynman, Griffiths and Resnick?

I know there are a lot of similar questions here but just hear me out. I am going to start self-studying quantum mechanics in a few days. I think I am going to use the MIT quantum mechanics 1 lectures as a starting point. But books will be essential as I spend most of my time in school. I have...