Two thermos flask are of same height and same capacity . One has a circular cross section while the other has a square cross section. Which of the two will transmit less heat and why ?
Answers
Answer: Circular thermos
Circular thermos will transmit less heat.
Reason: It is because, When Heat starts transmit then it needs more area to transmit.
So, We know that circle has less area than the Square.
That's why, In this question, Circular thermos will transmit less heat.
Because it has less area.
While, Square has more area to transmit heat.
we know that, Transmission of heat is directly proportional to the surface area of the body .
So, we can say that, Because of less area in circular thermos, Less Heat will be transmitted in Circular thermos.
Circle has less area to transmit heat and square has more
=> The area of a circle is πr2
=> The area of a square is s2
The two thermos flask has the same height and same cross sectional area .
They may or may not have the same volume .
Now what is volume ?
Volume = height × area of cross section
Volume of the flask with square
Let the sides be a .
Let the height be h .
Area of cross section = area of square with side ( a )
⇒ Area of cross section = a²
Volume = a²h
Volume of the flask with circle
Area of cross section with circle = π r² with radius r .
Volume = area of cross section × height .
Now we were told they have the same height and same capacity .
The first flask will be a cuboid and the second one will be a cylinder of the same height and the same volume .
Thus the area of cross section of the first flask will be more .
Obviously the square will have more area than the circular one .
So the square will transmit more heat .
The flask with circular cross section will transmit less heat .
NOTE :
Transmission of heat is directly proportional to the surface area of the body .