CBSE Class 12 Physics Conduction Solved Examples

CBSE Class 12 Physics Conduction Solved Examples. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Ex.1 A cubical ice box of thermocule has each side 30 cm and a thickness of 5 cm.4 kg of ice is put in the box. If out side temp. is 45° C and coefficient of thermal conductivity = 0.01 JS^–1 m^–1 °C^–1, calculate the mass of ice left after 6 hours. Take latent heat of fusion of ice = 335 × 10³ J/Kg.

Ex.2 An ice box made of 1.5 cm thick styrofoam has dimensions 60 cm × 60 cm × 30 cm. It contains ice at 0ºC and is kept in a room at 40ºC. Find the rate at which the ice is melting. Latent heat of fusion of ice = 3.36 × 105 J/kg. and thermal conductivity of styrofoam = 0.04 W/m–ºC.

Ex.3 Calculate approximately the heat passing per hour through the walls and windows of room 5 by 5 meters if the walls are of bricks of thickness 30 cms and have windows of glass 3mm thick and total area 5 square meters. The temperature of the room is 30º below that of the outside and the thermal conductivity of bricks and of glass is 12 × 10–4 and 25 × 10–4 C.G.S. units respectively.
Sol. Let Q1 be the heat passing through the walls, then

Ex.4 A compound bar 2m long is constructed of a solid copper core 1 cm in diameter surrounded by a steel casing whose outer diameter is 2cm. The outer surface of the bar is thermally insulated and one is maintained at 100ºC, the other is at0ºC.
(i) Find the total heat current in the bar.
(ii) What percentage is carried by each material. K for copper = 0.9 cal-cm–1sec–1(ºC)–1, and K for steel = 0.12 cal-cm–1sec–1(ºC)–1,

Sol. The compound bar is shown in fig. The rate of flow through copper bar is given by

Ex.5 A rod of negligible heat capacity has length 20 cm, area of cross-section 1.0 cm2 and thermal conductivity 200 W/m–°C. The temperature of one end is maintained at 0°C and that of the ether end is slowly and linearly varied from 0°C to 60°C in 10 minutes. Assuming no loss of heat through the sides find the total heat transmitted through the rod in these 10 minutes.

Ex. 6 A metal rod of length 20 cm and diameter 2 cm is covered with a non conducting substance. One of its ends is maintained at 100°C while the other end is put at 0°C. It is found that 25 g of ice melts in 5 min. Calculate the coefficient of thermal conductivity of the metal. Latent heat of ice = 80 cal gram–1