217 reputation
11
bio website butler.cc.tut.fi/~bossavit
location Paris, France
age 72
visits member for 3 years, 10 months
seen Jul 6 '11 at 19:41

Aug
7
awarded  Yearling
Mar
11
comment What is the electric field generated by a spinning magnet?
B is a vector field in my answer. So is M. Both are expressed in lab coordinates. If so, M varies with time, even though the magnetic moment M you use (a vector, not a vector field) is constant in time. Distinguishing magnetization (a vector field) and magnetic moment (the integral of the latter) is essential.
Mar
10
answered What is the electric field generated by a spinning magnet?
Mar
1
answered Physics for mathematicians
Mar
1
comment Time Dilation - How does it know which Frame of Reference to age slower?
I do agree it's overkill. But I want to make another point, for which it's not: That the issue is not "no acceleration, i.e. geodesic" versus "accelerations, i.e., non-geodetic worldline". One can schedule two trips with exactly the same episodes of acceleration-deceleration, only differently placed during the trips. The two worldlines are different, but both twins experiment the same total discomfort (or relief) due to acceleration (or lack of it). Yet, they age differently. This shows that differential aging is not (directly) caused by acceleration.
Mar
1
answered Time Dilation - How does it know which Frame of Reference to age slower?
Feb
16
comment Resistance between two points on a conducting surface
It's not "a certain amount of current" but an uncertain one. How much current flows in the situation you describe depends on unspecified parameters, mainly, the contact resistance, and/or the area of effective contact between the wire and the object.
Feb
15
answered Resistance between two points on a conducting surface
Feb
5
awarded  Teacher
Feb
5
answered How is a spherical electromagnetic wave emitted from an antenna described in terms of photons?