Earphone cable resistance
After some googling, earphone/headphone cables has 18-26 AWG gauge.
With the assumption we are using the thinnest cable (AWG 26), from the AWG gauge specification, the maximum current for chassis wiring is 2.2 A, and for power transmission is 0.361 A.

It has resistance 134 ohm/km or 0.134 Ohm/meter. Using this cable for 2 A, we can expect power dissipation 0.536 W/m and voltage drop 0.268 volt/meter that is very big.