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.
39. Which of the following arrangements of identical insulated copper rods, all having the same △T between the hotter end (H) and the colder end (C), will have the highest value of R?
Your Answer is
Correct Answer is A
Explanation
The rods in the four options have the same cross-sectional area and the same ΔT, so you only need to consider the impact of length on R;
According to figure 2, the smaller the length, the larger R. So choose A