Transmission of heat Questions and Answers

Consider a compound slab consisting of two different material having equal thickness and thermal conductivities k and 3k respectively as shown in figure The equivalent thermal conductivity of the slab is l l k 3k O O O 3k 2 4k 3

48 The inside and outside temperature of a refrigerator are 273K and 303 K respectively Assuming that refrigerator cycle is reversible for every joule of work done the heat delivered to the surrounding will be a 9J b 10J c 13J d 11J

The thickness of ice on surface of a lake becomes x cm and y cm starting from zero thickness in time t and to respectively If to 1 3 t 1 2 3 3 then 2 x y is equal

An arrangement consisting of slabs is shown in the figure When system is placed in situation a with temperature difference is maintained between 1 and 2 equivalent thermal conductivity of system is K and when system in changed to situation b and temperature difference is maintained between 3 and 4 then equivalent thermal conductivity increases by 20 Find number of slabs in the arrangement 22 21 d 24 nk b 4

Two thin concentric shells made of copper with radius r and r r r have a material of thermal conductiv K filled between them The inner and outer spheres are maintained at temperatures T and To respective by keeping a heater of power P at the centre of the two spheres Find the value of P H C

Consider two insulating sheets with thermal resistances R R and R as shown The temperature 0 is 1 2 3 0 4 2 Question Type Single Correct Type R 0 0 R R R R 0 0 0 R 0 R R R 01 02 R R R R 2 0 R 0 R D 0 R 1

Two containers A and B are connected by a conducting solid cylindrical rod of length 242 7 cm and radius 8 3 cm Thermal conductivity of the rod is 693 watt mole K The container A contains two mole of oxygen gas and the container B contains four mole of helium gas At time t 0 temperature difference of the containers is 50 C after what time in seconds temperature difference between them will be 25 C Transfer of heat takes place through the rod only Neglect radiation loss Take R 8 3 J mole K and 22 7 Report an integer A B

The two opposite faces of a cubical piece of iron Thermal conductivity 0 2 SI units are at 100 C in steam and 0 C in ice If the area of a surface is 4 m then the mass of ice melted in 10 minutes will be Approx Question Type Single Correct Type 1 35 g 2 300 g 3 7g

A black body is at a temperature of 2880 K The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is u between 999 nm and 1000 nm is u and between 1499 nm and 1500 nm is u3 The Wien constant is b 2 88 x 106 nm k Which of the following is correct A u 0 U U B u3 0 D U U

Calculate the rate of loss of heat through a glass window of area 1000 cm and thickness 0 4 c when temperature inside is 37 C and outside is 5 C Co efficient of thermal conductivity of gla 10 1 is 2 2 x 10 Cal s cm 2 3 Define co efficient of thermal conductivity and hence find its unit in SI A think ploce tumbler often cracks when boiling water is poured into it why

59 A system has non degenerate energy levels with energy E n 1 w where hw 8 625 10 5 eV and n 0 1 2 3 Calculate the probability that the system is in the n 10 state if it is in contact with a heat bath at room 300 K What will be the probability for the limiting cases of very low temperature and very high temperature temperature T

56 From observations on the intensities of lines in the optical spectrum of nitro gen in a flame the population of various vibrationally excited molecules rela tive to the ground state is found as follows V Ny No 0 1 000 1 0 210 2 0 043 3 0 009 Show that the gas is in thermodynamic equilibrium in the flame and calcu late the temperature of the gas 0 3 350 K

A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t The metallic rod is melted and the material is formed into a rod of half the radius of the original rod What is the amount of heat conducted by the new rod when placed in thermal contact with he two reservoirs in time t 2010 Pre d 20 a Q 2 b Q 4 c Q 16

5 Assume the sun to be a black body at temperature 5800K The total ra diant energy emitted by the Sun per second and the solar energy reach ing Earth s atmosphere per second is o 5 672x10 8 SI unit radius of the Sun 7x108m distance of the Earth s atmosphere from the Sun 1 5x10 m Take T 3 142 a 3 95x1020 J and 2 4kW m 2 b 3 95x1026 J and 1 8kW m c 3 95x1022 J and 1 4kW m 2 d 3 95x1026 J and 1 4kW m 2

61 A wire of length 1 m and radius 1 mm is heated via an electric current to pro duce 1 kW of radiant power Treating the wire as a perfect blackbody and ignoring any end effects calculate the temperature of the wire

A horizontal pipe 6 m long and 12 5 cm in diameter is maintained at a temperature of 150 C in a large room where the air is 20 C and 1 atm The walls of the room are at 38 C Assume that 0 7 for the pipe How much heat is lost by the pipe through both convection and radiation