# Homework Help: Some Basic Doubts

1. May 24, 2005

### Dr.Brain

OK ..actually i dont have any doubts generally but when I do some new chapters, i do have some.

I was reading about BAR MAGNETISM and about para,dia and ferro properties of materials. My first doubt:

1)How can "angle of dip" at the poles be 90 degrees? .. I think at the South Or North Pole , the bar magnet becomes verticle such that N always points in the direction of the net field.So It should make and angle of 0 degrees at the poles!!

2) What are the adverse effects of the Magnetic reversals that take place as for the earth's magnetic field dirction?

3)Suppose we have a bar magnet Of material A with pole strength "m" ... now we make another Bar magnet from same material A with length more than the previous one .. does its "m" change?

4) I think we can replace each coil of a solenoid by a bar magnet of pole strength "m" such that md=iA ..right? ... can we do something like replace the solenoid with only one bar magnet with same "m" as the previous method but length equal to that of solenoid's?

These are my own doubts.Thanx

2. May 24, 2005

### maverick280857

Your question 4 makes sense but you should know that the pole theory has long been abandoned and in India, it is taught only for historical reasons. Some of the books you may consult are older volumes of Resnick and Halliday (part II), Sears/Zemansky and perhaps your textbook as well.

For question 4, you already have half the answer in the question. The magnetic dipole moment is an assigned quantity and so equality of it for two distinct geometries merely implies (if the currents are unequal) the product of the three quantitites that make it up is equal. Further, if two bodies with the same magnetic dipole moment are kept in the same external field, they will experience the same (magntitude) of torque.

Cheers
Vivek

3. May 25, 2005

### HallsofIvy

How is "angle of dip" measured?? In other words relative to what? Oh, and I think you should specify north and south magnetic poles.