Question

(a) (i) How is the transference of heat energy by radiation prevented in a calorimeter ? 

(ii) You have a choice of three metals A, B and C, of specific heat capacities 900 J kg^-1 °C^-1, 380 / kg^-1 °C^-1 and 460 J kg^-1 °C^-1 respectively, to make a calorimeter. Which material will you select ? Justify your answer. 

(b) Calculate the mass of ice needed to cool 150 g of water contained in a calorimeter of mass 50 g at 32°C such that the final temperature is 5°C. Specific heat capacity of calorimeter 0.4 J g^-1 °C^-1 Specific heat capacity of water = 4.2 J g^-1 °C^-1 Latent heat capacity of ice 330 J g^-1 

(c) (i) Name the radiations which are absorbed by greenhouse gases in the earth’s atmosphere. 

(ii) A radiation X is focused by a particular device on the bulb of a thermometer and mercury in the thermometer shows a rapid increase. Name the radiation X. 

(iii) Name two factors on which the heat energy liberated by a body depends.

Answer 1

(a) (i) This is done by polishing the inner and outer surface of the copper calorimeter and the space between the copper vessel and the insulating container is filled with some poor conductor like wood wool or glass wool. 

(ii) A, as it will gain less energy in a given time. 

(b) Given m_w = 150 g, m_i = ?, m_C = 50 g, T_i = 0°C, T_w = 32 °C, T_f= 5°C 

Specific heat capacity of calorimeter = 0.4 J g^_-1 °C^-1 

Specific heat capacity of water = 4.2 J g^-1 °C^-1 

Latent heat capacity of ice 330 J gm^-1 

Heat lost by 150 g water + 50 g of calorimeter in falling form 32°C to 5°C 

= 150 × 4.2 × 27 + 50 × 0.4 × 27 = 17550 J 

Heat needed to melt ice = m_i L = m_i × 330 = 330m_i So 330m_i = 17550 or mi = 17550/330 = 53.2 g 

(c) (i) Infrared 

(ii) Infrared 

(iii) Temperature and surface area.