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?

Step-by-step

Given I = V/R

and

I = 100 mA = V0 / R0

What is the new current (I) when resistance is halved (half the length of original) and voltage is doubled (12 to 24V)

Solution:

given: I = 100 mA = V0/R0

new current, I' = V0*2 / (R0/2) = 4 * V0/R0 = 4*100 mA = 400 mA

just a quick addition, to the risk of sounding redundant.

now, we know R = L, so if we cut the length in half, namely L/2, will also mean we're cutting the resistance amount by half, R/2 = L/2 on that direct variation.

so what would the current "I" be if 3/25 gets halved and V = 24 volts ?