Which of the following circular rods, (given radius r and length l) each made of the same material and whose ends are maintaind at the same temperature diff. will conduct most heat ?

Options

A. `r=2r_(0),l=2l_(0)`
B. `r=r_(0),l=2l_(0)`
C. `r=2r_(0),l=l_(0)`
D. `r=r_(0),l=l_(0)`.

Answer

C

Explanation

`(c ):(dQ)/(dt)=KA(dT)/(dx)`
Since `A=pir^(2)` and `dx=l`
`:.(dQ)/(dt)prop(r^(2))/(l)`
Now `(r^(2))/(l)` will be maximum
when `r=2r_(0)` and `l=l_(0)`
Coorect choice is (c ).