## Sunday, April 10, 2016

### New batches at Madgoan, GOA, India

Hey Boys and Girls,

I am Starting New batches at Madgoan, GOA, India.
You May Refer or Informed  Your Friends in GOA.

Classes for - IIT-JEE, GCET, Board,

Thanks
DMR

## Monday, September 8, 2014

### Simple Thoughts

Hello All,

Just to keep you people motivated, I have created a page on Facebook that is "Simple Thought". You may liked this page on Facebook and be motived.

Simple Thought page links is below on right side.

Regards
DMR

## Thursday, April 24, 2014

### What is a unit?

Question 1: What is a unit?

## Wednesday, April 23, 2014

### Dear Students,

Welcome to your new classes 11th and 12th.

Let's use this blog as much as possible. You are free to ask any question related to physics and I will try to answer your question as quickly as possible.

Please ask your friends to join this group. It is 100% free online tutorial for you all.

Regards
DMR

## Saturday, January 12, 2013

### Torque on a Bar Magnet in a Magnetic Field

Let a bar magnet makes angle θ with magnetic field B and 2l be the length of the bar as show in figure.

Force on N-pole = mB along B and Force on S-pole = mB, opposite to B, since these are the equal and opposite forces they produce torque

ז = force x perpendicular distance. = mB x NA = mB x 2lsinθ therefore ז =MBsinθ

The direction of the torque is perpendicular to the the plain containing M and B, and given by right handed screw rules.

Magnetic dipole moment as the torque acting on a dipole held perpendicular to uniform magnetic field of unit strength

SI unit of M is JT-1

### Bar Magnet as an Equivalent Solenoid

To demonstrate the similarity of a current carrying solenoid to a bar magnet, let us calculate axial field of a finite solenoid carrying current.

Consider:           a = radius of solenoid
2l = length of solenoid with centre O
n = number of turns per unit length
I = current passing through solenoid
OP = r

Consider a small element of thickness dx of solenoid at distance x from O. and number of turns in element = n dx.
We know magnetic field due to n turns coil at axis of solenoid is given by

It is clear from the above expression that magnetic moment of a bar magnet is equal to the magnetic moment of an equivalent solenoid that produce the same magnetic field.

### Current Loop as a Magnetic Dipole

When we see a current carrying loop from top, current direction is anticlockwise and has north polarity. If, lower face of loop is seen from bottom then current direction is clockwise and have south polarity. Overall it behaves as a magnetic dipole depends upon

It is the magnetic moment of one turn loop of area one square metre carrying a current of one ampere.

NI factor is called as ampere turns of circular current loop