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b) The classical Dulong - Petit Law states that Cv = 3R where R is the ideal gas constant and C is the heat capacity at constant volume. However, experimentally Cy is found to vary with temperature as shown in Figure 1 at low temperatures i. ii. Cy 3R 0 T Figure 1 Use the Debye theory to explain the behavior of Cv Show that at low temperatures, C, varies as T³ (20 marks)