# Griffiths 7.7

I'm not taking this course for credit...

Hi! Is this a good text after Halliday?
I'm trying problem 7.7-
a metal bar of mass m slides frictionlessly on 2 conducting rails...
perhaps the current is I=integral J dot da, generated by the moving metal bar, velocity v (results in changing reference frame and B field which results in EMF driving current vertically up through the wire?) is the force diagram similar to 7.11?
I'm unclear on the geometry of the force digram?

thanks very much

Last edited:

## Answers and Replies

Related Advanced Physics Homework Help News on Phys.org
I'm curious at what point does a great physicist have the intuition for these problems- is it something that you are born with?

Do you know how to find the magnetic force on a stationary wire that is carrying current?
I wouldn't think about current density in a problem like this; it is intuitive to me that the total current through the bar is what matters for the force, regardless of the cross sectional distribution of current density.

Biot-Savart law

thanks very much!
Isn't that the beautiful Biot-Savart law where muo is the permeability of free space? uo=4pi*10^-7N/A^2)
(muo/4pi)Integral[ (I X r )dl'/r^2 ]

there is the interesting situation of the Infinite Wire- theta1=-pi/2, theta2=pi/2B= muoI/(2pi s)
and as you know there is a form for surface and volume currents
I'm just starting to look at these...

Last edited: