Two identical slabs are welded end to end 20 cals of heat flows through it in 4 min. If the two slabs are now welded by placing them one above the other, and same heat is flowing through two ends under the same difference of temperature, the time taken is :

Options

A. 1 min
B. 4 min
C. 6 min
D. 16 min

Answer

A

Explanation

Here `(t_(1)A_(1))/(x_(1))=(t_(2)A_(2))/(x_(2))`
`t_(2)=t_(1)(A_(2)x_(2))/(A_(2)*x_(1))`
when welded together the area becomes twice and length becomes half.
`t_(2)=(4xxA_(1)((x_(1))/(2)))/(2A_(1)*x_(1))="1 min"`.
Thus correct choice is (a).