39 40 in further 10 minutes it will cool from 38 C to A 36 C

23 A body of length 1 m having cross sectional area 0 75 m has heat flow through it at the rate of 6000 J s The difference between two ends of conductor if K 200 J m K 1 is 40 C 100 C 1 20 C 3 80 C 2 4 onductivities 2

4 35 A rod of length with thermally insulated lateral surface and cross sectional area A consists of material whose heat conductivity coefficient varies with temperature as k a T where a is a constant The ends of the rod are kept at temperatures T and T T T Find the function 7 x where x is the distance from the end whose temperature is T and the heat flow density 2 2 Ans T x T T T q a l In T T

Four square pieces of insulation are available to cover an opening area 2A They are of different materials with conductivities K and K as shown and arranged as shown for case I and case II They are of same thickness and area A Find the correct option to ensure lesser heat flow K K K K Case I O Case Il O Case 1 O Equal heat flow O Unpredictable K K K K Case Il

4 similar rods which are thermally insulated are joined at point A If heat flows in from point B at rate of 1W and from point C at 3W inside flows out from D at 5W which relation is correct for temperature of these points A TA TE B TB Tc B C X E D C Tc TD D TB TE

A hollow spherical ball of inner radius a and outer radius 2a is made of a uniform material of constant thermal conductivity K The temperature within the ball is maintained at 2T and outside the ball it is T Find a the rate at which heat flows out of the ball in the steady state b the temperature at r 3a 2 where r is radial distance from the centre of shell Assume steady state condition AOL 0 2a a 2TO K T

A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K If the radius were halved and the temperature doubled the power radiated in watt would be NEET 2017 1 225 2 450 3 1000 4 1800

0 Certain quantity of water cools from 70 C to 60 in the first 5 minutes and to 54 C in the nex minutes The temperature of the surroundings i AIPMT 20 1 45 C 2 20 C 3 42 C 4 10 C

The top of the lake is frozen The air in contact with surface of lake is 20 C Then the maximum temperature of water in contact with lower surface ice will be 6 C 10 0 C C 273 C English

Example 22 13 A cylinder of radius R made of a material of conductivity K is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K The two ends of the combined system are maintained at two different temperatures There is no loss of heat across the cylindrical surface and the system is in steady state The effective thermal conductivity of the system is JEE 1998 a K K c K 3K 4 b K K K K d 3K K 4 Solution Let R and R be the thermal resistances of inner and outer portions Since temperature difference at both ends is same the resistances are in parallel Hence or bow 2R option is c Fig 22 16 1 RR R 1 R 1 KA KA 1 K R K 4 R K R K 3 R 1 1 1 ban K 3K 4 09 01 SS olgm 028 no

Six identical conducting rods are joined as shown in figure Points A and D are maintained at temperature of 200 C and 20 C respectively The temperature of junction B will be R A 200 C 1 120 C 3 140 C C B 2 100 C 4 80 C D 20 C