r***o
发帖数: 6 | 1 A uniformly charged spherical ballon deflates suddenly,maintaining
its spherical shape and total charge.
which of the following statements concerning the possible emission
of electromagnetic radiation during this process is true?
(a) Radiation is emitted because charge is accelerated.
(b) Radiation is emitted because the surface density of charge increases
(c) No Radiation is emitted because there are no magnetic fields present.
(d) No radiation is emitted because charge is conserved.
(e) No rad | M*********m
发帖数: 2024 | 2 There are several ways to consider this problem. You can compute the
electromagnetic energy generated by the charges. Outside the sphere, the
electric field is Q/r^2, inside the sphere, the electric field is zero. So the
static electromagnetic energy is Q^2/(2R). When R increases, the
electromagnetic energy is lowered and so the difference in energy is radiated.
Another way to consider the system is that for radius equals infinity, that's
the lowest energy of the system and choose it as zero. Fo
【在 r***o 的大作中提到】
: A uniformly charged spherical ballon deflates suddenly,maintaining
: its spherical shape and total charge.
: which of the following statements concerning the possible emission
: of electromagnetic radiation during this process is true?
: (a) Radiation is emitted because charge is accelerated.
: (b) Radiation is emitted because the surface density of charge increases
: (c) No Radiation is emitted because there are no magnetic fields present.
: (d) No radiation is emitted because charge is conserved.
: (e) No rad
| s********k
发帖数: 107 | 3 I think the answer should be E.
First, Let's consider the direction of E and H in some point A outside of the
ballon. According to the symmetry, E should be along radial direction. And
since S=E x H, So we know the compaonet of S along the radial direction is 0.
We can even consider something about H to get more insteresting result. As well
according to mirror symmetry and H is a pseudovector, the radial component of
H is 0. But due to sphericaly symmetry, H should be along radial direction, so
【在 r***o 的大作中提到】
: A uniformly charged spherical ballon deflates suddenly,maintaining
: its spherical shape and total charge.
: which of the following statements concerning the possible emission
: of electromagnetic radiation during this process is true?
: (a) Radiation is emitted because charge is accelerated.
: (b) Radiation is emitted because the surface density of charge increases
: (c) No Radiation is emitted because there are no magnetic fields present.
: (d) No radiation is emitted because charge is conserved.
: (e) No rad
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