A weld with a triangular cross section as shown below is to be produced on a steel work piece by shielded metal arc welding operation using steel electrode. If a 24 V power supply is used and the welding speed is 12 mm/s, what is the current needed? Assume the efficiency as 80% and the specific energy to melt steel as 8 J/$$mm^3$$.

Correct option is C

​$$\textbf{Given:}\\\begin{aligned}&\bullet \ \text{Cross-section: Right triangle with 5 mm height and } 45^\circ \text{ angles} \\&\bullet \ \text{Voltage } V = 24 \, \text{V} \\&\bullet \ \text{Welding speed } v = 12 \, \text{mm/s} \\&\bullet \ \text{Efficiency } \eta = 80\% = 0.8 \\&\bullet \ \text{Specific energy to melt steel} = 8 \, \text{J/mm}^3\end{aligned}$$

$$A = 2 \times \frac{1}{2} \times 5 \times 5 = 25 \,\text{mm}^2 \\[8pt]V = A \times \text{speed} = 25 \times 12 = 300 \,\text{mm}^3/\text{s} \\[8pt]Q = 300 \times 8 = 2400 \,\text{J/s} \,(\text{W}) \\[12pt]Q = \eta \times V \times I \\[6pt]2400 = 0.8 \times 24 \times I \\[6pt]I = \frac{2400}{19.2} = 125 \, \text{A}$$​​​​