hate_xams
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#1
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Can anyone tell me what the answer is, this question was just in my AS physics exam:

Express the volt in terms of the SI base units: kg, m, s and A
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Knogle
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kg m2 s-3 A-1
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hate_xams
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Ok, any chance you could put the working of that up?? Thanks
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teachercol
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Volts = Joules / Coulombs

Joules = Newton x metre

Coulomb = Amp * second (edit oops)

Newton = kg x metre / second squared

Put it all together.
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Knogle
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Voltage = Power/Current
Power = Energy/Time (Joules/second)
Energy = Force * Distance
Force = Mass * Acceleration (Newton's 2nd law)

=> SI base units of Force: kg m s-2
=> SI base units of Energy: kg m2 s-2
=> SI base units of Power: kg m2 s-3
=> SI base units of Voltage: kg m2 s-3 A-1
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hate_xams
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#6
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Thanks!!
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Knogle
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#7
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Bitteschon. :gthumb:
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john-boro
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hey, isn't the charge a more 'base' unit than current?
in which case it would be N m C^-1
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Mehh
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(Original post by john-boro)
hey, isn't the charge a more 'base' unit than current?
in which case it would be N m C^-1
Not in SI it seems. On top of those above there is also the Kelvin Candela and Mole.
Its actually quite logical. The Ampere predated the Coulomb.
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forkwise
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Yes, but I think he meant that current is the rate of flow of charge, (Q/t) so one would assume that charge should be the base unit. I know it's not :p:
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john-boro
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Having said that, charge was defined to me as 'one coulomb is the charge that is transferred when one amp flows for one second'. So I guess you're right, Amperes are the 'first' unit and so the SI one. It just seems weird because usually things are not defined as a product of time and another thing. Like a metre isn't defined as the distance moved when something going 1m/s moves for 1 s. Or maybe it is :p:

weird anyway
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SunGod87
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Metre is defined: The length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second.
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john-boro
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ahh that's interesting thanks. A second is defined as something to do with caesium is it not, so in that way it does look like the time-related thing is more fundamental.
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