Post History
Is the answer of 1/c seconds correct It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance...
Answer
#3: Post edited
by
Olin Lathrop
·
2021-11-23T22:27:29Z (almost 3 years ago)
- <blockquote>Is the answer of 1/c seconds correct</blockquote>
- It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance.
- <hr>
- <blockquote>In this case, 1 is 1 meter</blockquote>
"1" is never one meter. "1 m" or "1 meter" is one meter.
- <blockquote>Is the answer of 1/c seconds correct</blockquote>
- It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance.
- <hr>
- <blockquote>In this case, 1 is 1 meter</blockquote>
- "1" is never one meter. "1 m" or "1 meter" is one meter.
- Added: I guess a discussion of the physics has been delayed long enough so that there have been enough consequences for the sloppy use of units.
- <hr>
- One answer discussed propagation of current down the wire and radio propagation from the switch to the light bulb. There is another possibility, which is the transmission line effect.
- If each out-and-back segment at left and right were a transmission line, then current would be induced in the far conductor very quickly. Another way to think of the same thing is that the near wire is the primary of a transformer, and the far wire the secondary. When current changes in the primary, there will be an induced voltage in the secondary.
- In this case, with the near and far wires being 1 m apart, that coupling is rather weak. Most of the magnetic field produced by the current in the near wire won't wrap around the far wire. The energy transfer between the two will therefore be minimal. Another way to put this is that the transformer has large leakage inductance, and small coupled inductance.
- If the two wires were right next to each other, then this effect could be significant. With perfect coupling and 0 wire resistance, any current in the primary wire would immediately cause an equal and opposite current in the secondary wire, which causes the magnetic field to stay at 0. In that case, the light bulb would light almost instantly. In the case actually presented, a tiny voltage could be detected after the magnetic field propagated from the front to the back wire. The bulb lighting would have to wait until the current propagates in the wire to the bulb.
#2: Post edited
by
Olin Lathrop
·
2021-11-22T13:04:58Z (almost 3 years ago)
- <blockquote>Is the answer of 1/c seconds correct</blockquote>
It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance.
- <blockquote>Is the answer of 1/c seconds correct</blockquote>
- It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance.
- <hr>
- <blockquote>In this case, 1 is 1 meter</blockquote>
- "1" is never one meter. "1 m" or "1 meter" is one meter.
#1: Initial revision
by
Olin Lathrop
·
2021-11-21T14:52:11Z (almost 3 years ago)
<blockquote>Is the answer of 1/c seconds correct</blockquote> It can't possibly be. The question is looking for a time value. "C" is a speed, which has units of distance/time. "1/c" therefore has units of time/distance.