# MHD equation

1. Apr 24, 2007

### delta001

dB/dt = -curl E

The change in the magnetic field over time is equal to the negative curl of the electric field. Interesting. How do I use it to solve a real life problem?

2. Apr 25, 2007

### lpfr

In this differential form, I think that it is of no use in any practical problems. But if you take a surface and integrate this formula over the surface, you will get the Faraday's Law, which powers your PC and lights yours lamps.

3. Apr 25, 2007

### Mentz114

Combine it with dE/dt = curl B and it powers your eyes.

4. Apr 25, 2007

### lpfr

Is light a real life problem?

5. Apr 25, 2007

### neu

no it's a fake life problem. what do you mean?

6. Apr 25, 2007

### lpfr

I mean that you should answer at the question posted and this at an adequate level. delta001 can probably solve problems using the Faraday's Law. But, even when you work with light, do you use dB/dt = -curl E ? No, you don't and neither delta001 (neither me).
This is the reason why I found your post inappropriate.

7. Apr 25, 2007

### Mentz114

I was joking. But what is the motive for the OP's question ?

Does Delta001 think that this fact is not worth knowing, simply because it's not used in everyday computations ? It is, after all one of Maxwell's equations.

8. Apr 25, 2007

### delta001

You semi-presume much of me. My motives are what I originally asked. I am generally curious about how to use it, nothing else.

9. Apr 25, 2007

### ZapperZ

Staff Emeritus
1. Why did you call it "MHD equation"? Is "Maxwell Equations" out of fashion already?

2. In "real life", most of these type of equation cannot be solve analytically. In the design of waveguides and RF structures, for example, we use this and other coupled equations that we solve numerically. So when you look at some radio transmitter or antenna, those are a few examples where that equation has been used and solved.

Zz.

10. Apr 25, 2007

### Mentz114

Delta001, you are right, it was wrong to infer a dark motive. Peace.

But that equation, in context tells us a lot about the EM field, and should be used as 'mind food' rather than as a computational aid.