Question

Spot welding of two $1mm$ thick sheets of steel (density $=8000kg/m^3$) is carried out successfully by passing a certain amount of current for $0.1$ second through the electrodes. The resultant weld nugget formed is $5mm$ in diameter and $1.5mm$ thick. If the latent heat of fusion of steel is $1400kJ/kg$ and the effective resistance in the welding operation is $200\mu \Omega$, the current passing through the electrodes is approximately

• A. $4060A$
• B. $3300A$
• C. $9400A$
• D. $1480A$

Answer 1

The correct option is A $4060A$

$\text{Mass}=\frac{\pi }{4}\times 25\times 1.5\times 8000\times {10}^{-9}$

$=2.356\times {10}^{-4}kg$

$\text{Heat generated}=140\times 8000\times 2.356\times {10}^{-4}$

$=329.8J$

$\text{Heat generated}=I^2\times R\times t$

$329.8=I^2\times 200\times {10}^{-6}\times 0.1$

$I=4060\text{amp}$