marinacalder
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The International Space Station orbits just above the atmosphere every 90 minutes. Use
this to calculate the radius of the Earth.
Now, considering the Earth as an isolated, charged sphere, what is the capacitance of the Earth.
Comment on your answer.
[In the ISS’s low-earth-orbit, gorbit ≈ gsurf ace . ε0 = 8.9 × 10−12 F/m.]



Is it reasonable to use just mg=mv^2/r here since gorbit ≈ surf ace?
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HoldThisL
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I probably should've paid attention in GCSE physics at least.
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K-Man_PhysCheM
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(Original post by marinacalder)
The International Space Station orbits just above the atmosphere every 90 minutes. Use
this to calculate the radius of the Earth.
Now, considering the Earth as an isolated, charged sphere, what is the capacitance of the Earth.
Comment on your answer.
[In the ISS’s low-earth-orbit, gorbit ≈ gsurf ace . ε0 = 8.9 × 10−12 F/m.]



Is it reasonable to use just mg=mv^2/r here since gorbit ≈ surf ace?
Yes, that's fine. Hence why it is given to you as information in the question
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Physics Enemy
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(Original post by marinacalder)
...
Thought I'd comment you've assumed electrostatic force here is negligible and/or F (grav) >> F (electro), which is prob fine.

And yes if you can assume g_o ~ g_e, you can write mv^2/r = GMm/r^2 ~ mg_e and go from there.
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Pangol
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(Original post by Physics Enemy)
Thought I'd comment you've assumed electrostatic force here is negligible and/or F (grav) >> F (electro), which is prob fine.
Surely this is a perfectly acceptable assumption. Electromagnetism may be a stronger force than gravity in absolute terms, but any net charge on the ISS (and even the Earth) is going to be pretty inconsequential.

The capacitance question in nice, even though I can't see the Earth ever being charged up to act in this way!
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Physics Enemy
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(Original post by Pangol)
Surely this is a perfectly acceptable assumption. Electromagnetism may be a stronger force than gravity in absolute terms, but any net charge on the ISS (and even the Earth) is going to be pretty inconsequential.

The capacitance question in nice, even though I can't see the Earth ever being charged up to act in this way!
I agree, but I thought it was worth mentioning, esp as the next bit talks about the earth's charge. Sometimes it's easy to forget there's also an inconsequential F (electro) that we can get away with ignoring.
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marinacalder
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I found this suspiciously easy... am I doing something wrong, or am I getting into the swing of things?:cute:
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Pangol
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(Original post by marinacalder)
I found this suspiciously easy... am I doing something wrong, or am I getting into the swing of things?:cute:
It does strike me as being much easier than some of the other questions you've posted, but I can't see how it can be harder than the above discussion indicates. Having said that, the capacitance of a spherical capacitor doesn't appear that often at A level.
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