Problem Solving Strategies

4:18 AM

Hello sir

@PrateekMourya hi :-)

Is there any intuitive way to understand tensors?

@PrateekMourya If there is I don't know it :-)

My teacher said moi is tensor it doesn't follow vector algebra

I mean like last time you demonstrated minkowski tensor

A: What is the direction of moment of inertia in a system?

Ah, as it happens I have just answered a question on exactly this topic. Give me a moment and I'll find the link.

The angular equivalent of Newton's second law is: $$ \tau = I \alpha $$ where $I$ is the moment of inertia, $\tau$ is the torque and $\alpha$ is the angular acceleration. At first glance it looks as if $I$ is just a scalar, but it turns out to be more complicated that this. To see why consider ro...

4:43 AM

Sir what was first defind moment of inertia or torque?

The way I would view the MOI is that it converts an angular acceleration to a torque.

That is, it takes a vector as input and produces a second different vector as output.

Whenever i deal with something defined i try to find what benefits of it defining this way

There are lots of cases in physics where this happens and we need tensors.

Wikipedia says euler defined moi

For example if I apply an electric field to something it will polarise that object and the object will develop an electric dipole:

p = P E

4:47 AM

Ah diapole

I also have a question about

where P is the polarisibility.

That

Is diapole just defined or is it some phenomenon

I read in my chemistry book

And since both the field E and the dipole p are vectors, the polarisibility P must be a tensor.

Which indeed it is.

Current too is tensor?

No, but the resistivity is.

The bulk version of Ohm's law is E = ρ J where J is the current density and E is the electric field strength. Yes?

4:50 AM

Sorry sir i may not be able to follow i am 11th grader and electricity is in 12 th

Just my sir gave an example that current is a tensor

It has direction

But doesn't follow vector rules

Current is not a vector or a tensor.

Current density is a vector.

Ok i will remember that in future

(current density is the current per unit area)

Is diapole moment for molecule just defined

Do you have an existing answer for diapole moment?

There is a formula for calculating the dipole moment from the charges present.

4:53 AM

I mean is diapole moment a phenomenon?

In a molecule that has a dipole moment we get some charge separation i.e. one end is a bit more positive and the other end is a bit more negative.

When we feed these charges into our equation for the dipole we can calculate its value for that molecule.

The simples dipole is two point charges +q and -q separated by a distance d, and the dipole moment is p = qd

So its just defined

Not really. The equation for the dipole wasn't just made up.

It comes from group theory, but the details are complicated.

4:57 AM

Oh so that's why i cant find it in any of the textbooks

For jee

Yes, at JEE level you have to just accept the way a dipole is defined.

You also don't need to know about tensors for the JEE. You'll only learn about them if you do a physics degree.

Why Raindrops Are Mathematically Impossible

Ok sir

►

Sir i have confusion related to this video

Why we cant take units smaller so that the number are no lomher less tham 1

Sorry avoid typing mistake:)

Give me a few minutes and I'll watch the video ...

5:24 AM

Ok sir

Jack Rod

@ManasDogra can you think what kind of trajectory it will follow?it is a hint

Annamalai Sriram

6:00 AM

@ManasDogra From where did you take that question?

@ManasDogra ping me when you're around. This is simpler than it looks. The motion needs to look like this:

i.e. in the field the charge moves in a circle with some radius r and we need that circle to just graze the outer circle so the particle returns to the inner circle again.

Although it looks complicated at first sight there is a really simple way to calculate r in terms of a and b.

6:54 AM

@JohnRennie sir please ping me once you are free..

7:25 AM

@satan29 hi

2 hours later…

9:07 AM

@JohnRennie hi sir

@satan29 hi :-)

oh man, my room got frozen!!!

You could ask in hbar if a mod would be willing to unfreeze it.

i have created a new one for now

8 hours later…

Manas Dogra

4:51 PM

From this diagram, I found the radius..Thanks
I drew the wrong circle...I drew one with centre on the X axis with centre at ((a+b)/2,0) and radius (b-a)/2,i.e.,the circle touches (a,0) and (b,0) as diametrically opposite points on it...

@JackRod Circular...But I drew the wrong circle..not quite sure why its wrong...

@AnnamalaiSriram It's from IIT JAM physics postgrad entrance exam of 2020.

I knew it comes from the multipole expansion of potential...

From Group theory? Can you mention a reference from where I can read that...I know introductory group theory at the level of Tung.