A block of metal is 2 cm ˛ 3 cm ˛ 5 cm. When one of the 2 cm ˛ 3 cm faces is held at a temperature T1 and the
other at a temperature T2, the heat flow through the block is P. In terms of P, what is the heat flow when one of
the 2 cm ˛ 5 cm faces is held at a temperature T1 and the other at a temperature T2?
A) (25/9)P B) (9/25)P C) (9/4)P D) (75/12)P
other at a temperature T2, the heat flow through the block is P. In terms of P, what is the heat flow when one of
the 2 cm ˛ 5 cm faces is held at a temperature T1 and the other at a temperature T2?
A) (25/9)P B) (9/25)P C) (9/4)P D) (75/12)P
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dQ/dt = -kA (dT/dx)
Heat flow is proportional to area and inversely proportional to the length over which its flowing. The area of the first face is 2*3 = 6 cm^2. The area of the second face is 2*5 = 10 cm^2.
The length in the first case is 5 cm. The length in the second case is 3 cm.
So the heat flow in the second case is (10/6) * (5/3) compared to the first case.
Heat flow is proportional to area and inversely proportional to the length over which its flowing. The area of the first face is 2*3 = 6 cm^2. The area of the second face is 2*5 = 10 cm^2.
The length in the first case is 5 cm. The length in the second case is 3 cm.
So the heat flow in the second case is (10/6) * (5/3) compared to the first case.
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The different in surface area between the first and second scenario is that of 25/9 since 5^2 = 25 and 3^2=9