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# Vector Calculus (Maxwell's equations and the Poynting Vector) Watch

1. Q5 here: http://www.damtp.cam.ac.uk/user/examples/A5d.pdf

Really have no idea where to go with this. I have no idea where c^2 could possibly come from and I tried finding dpi/dt and got to this:

And frankly I think all of that is absolute rubbish.

Any help would be appreciated.

Thanks
2. I think you've done some unnecessary steps - it should become a bit clearer if you use that , and I would find dT/dxi too (you then see some structural similarity).
3. (Original post by Smaug123)
I think you've done some unnecessary steps - it should become a bit clearer if you use that , and I would find dT/dxi too (you then see some structural similarity).
Right, okay. I'm not too sure how to differentiate the first part of Tij (the part with delta ij). It's just a scalar multiple of the identity matrix right? I'm not too sure what to do with that.
4. (Original post by Intriguing Alias)
Right, okay. I'm not too sure how to differentiate the first part of Tij (the part with delta ij). It's just a scalar multiple of the identity matrix right? I'm not too sure what to do with that.
You can treat the delta function with differentials just as normal: .
5. (Original post by Smaug123)
You can treat the delta function with differentials just as normal: .
I managed it now, thanks for the help.
6. (Original post by Intriguing Alias)
I managed it now, thanks for the help.
No problem I should really do that sheet - my supervisor gives us different ones, the questions are broadly the same, but I see that the official sheets have much more Maxwell in them, so if that's a hint as to what will come up in the exam…

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