In a DC arc welding operation, the voltage-arc length characteristic was obtained as $V_{arc} = 20+5l$ where the arc length $l$ was varied between $5$ mm and $7$ mm. Here $V_{arc}$ denotes the arc voltage in $Volts$. The arc current was varied from $400$ A and $500$ A. Assuming linear power source characteristic, the open circuit voltage and the short circuit current for the welding operation are