Passage VII
When a temperature difference (△T) exists between the ends of an insulated metal rod (see Figure 1), heat flows from one end of the rod to the either. (△T = TH - TC, where TH and TC represent the temperature of the hotter end and the colder end, respectively.)
The rate at which heat flows is called the heat transfer rate, R.
The following data apply to insulated copper rods. Table 1 gives R versus △T for a 5 cm long rod with a cross-sectional area of 3 cm2. In Figure 2, R is plotted against length for rods having a △T of 30℃ and a cross-sectional area of 3 cm2. In Figure 3, R is plotted against cross-sectional area for 5 cm long rods with a △T of 30°C.
37. A and B are both insulated copper rods. Based on Figure 3, if B has the same length and △T as A, but B has double the cross-sectional area of A, the ratio of R for B to R for A will be:
Your Answer is
Correct Answer is C
Explanation
It can be seen from figure 3 that the larger the cross-sectional area is, the larger the R is, and the two are proportional. So the cross-sectional area of B is twice that of A, so R(B):R(A)=2:1