# Recent content by Umrao

1. ### SR: Does observation change when changing reference frame

I meant how can the door close from rod's frame of reference if garage was too small? rod can't get outside garage from behind. The door wont shut no matter how long rod based observer waits
2. ### SR: Does observation change when changing reference frame

What if we close the gate for the garage when the rod was inside the garage? Also, assume that once the door was closed the rod can't get out so either it bends or breaks.
3. ### SR: Does observation change when changing reference frame

Actually, I just generalised the length of rod and garage in terms of L, the rest is given as an explanation in Relativity special, general and cosmological by Rindler (2006 edition - 3rd chapter), including the explanation about mechanical pressure travelling through the rod. I also read...
4. ### SR: Does observation change when changing reference frame

Homework Statement Special relativity: A rod travelling with the relativistic velocity of 0.866c moving towards a garage. The length of the rod is L, that of the garage is L/2. From the reference frame of the garage, we find the value of Lorentz factor = 2 we say that rod would fit inside...
5. ### IIT JEE problem (capacitors)

Yeah, I did get that
6. ### IIT JEE problem (capacitors)

Hey everyone, I am thinking something completely different and it is quite possible that I am wrong, so forgive me if I turn out to be wrong. The way I am thinking this problem to be is that, since it is given that balls attain same potential as the plate (as they had a metal film), so from...
7. ### Calculation of force due to electric dipole

Thanks a lot guys. Apparently I should add a word of caution while treating system of charges as dipoles, I got the answer by both electric field and using dipoles method. Winding up both 11th and 12th class isn't the easiest thing to do, I have been using binomial theorem to get approx...
8. ### Calculation of force due to electric dipole

Did you by any chance use, E= KQx/(R^2 + x^2)^3/2 for both rings and substract (or add depending upon you, if you think in terms of magnitude or vectors) and use binomial expansion? My point is - that is how we deduce electric field due dipole - so using superposition, or result of dipole...

Ah! now I get the result of post no. 9. Now I recall that I did a similar question on calculating electric field inside a cavity in an insulator having uniform charge density. Quite similar. But a question, how does this figure look anything like in post 4 or 6. Edit: I mean - here we are using...

That was a very misleading question - the link provided by Nidium tells that magnetic field is vertical "at the centre". While a comparison with Solenoid will make it appear as if it will have a constant vertical field
11. ### Taking the derivative of position to get velocity

I may be wrong but here is what I think - To take cosine, sine etc. you need to have an angle. Clearly it is changing in the equation -as shown- with time. say at time equals to one second - (notice that second in denominator and that of time are going to vanish with each other) - the angle is...