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# I'm confused!

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In physics, Ohm's law says that current through a wire, \(I\), is directly proportional to voltage, \(V\), and inversely proportional to resistance, \(R\):

\(I = V/R\)
It's also true that resistance is directly proportional to the length of the wire. We have a piece of wire. We pass 12 volts through this wire and measure 100 milliamps of current. If I cut the wire in half and pass 24 volts through it, how many milliamps of current will I measure?

Sep 19, 2018

#1
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Ok.. if we have a resistance of R ohms in a piece of perfect wire we will hve R/2 ohms in half that length of wire.

If we pass 12 volts through and measure 100 mA of current we have 12/(0.1) = 120 Ohms of resistance in the wire.

If we cut it in half we will only have 60 Ohms of resistance in the wire.

So if we pass 24 volts through it we will measure 24v/60ohs = 0.4 Amps = 400 mA of current

I can also quickly see this by noting that we halve the resistance and double the voltage.

2/(1/2) = 4, so we increase the original current by a factor of 4.

Sep 19, 2018
#2
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Thanks!!

HelpPLZ  Sep 20, 2018