Question

Two rods A and B of different materials are welded together as shown in Fig. If their thermal conductivities are k1 and k2 , the thermal conductivity of the composite rod will be

                                                        

Solution

Correct option is

 

 

If the ends of the rods are maintained at temperatures  and , the rate of flow of heat through each rod is given by

                          

 And                  

Where A is the cross-sectional area of each rod and d is the length of each rod. Now the cross-sectional area of the composite rod is 2A. If k is the thermal conductivity of the composite rod, the rate of heat flow is

                           

But                       Therefore

     

or                      ).

SIMILAR QUESTIONS

Q1

100 g of ice at 0oC is mixed with 100 g of water 80oC. The final temperature of the mixture will be

Q2

Steam at 100oC is passed into 1.1 kg of water contained in a calorimeter of water equivalent 0.02 kg at 15oC till the temperature of the calorimeter rises to 80oC. The mass of steam condensed in kilogram is

Q3

If there are no heat losses, the heat released by the condensation of xgrams of steam at 100oC into water 100oC converts y grams of ice at 0oC into water at 100oC. The ratio y/is nearly

Q4

One mole of oxygen is heated from 0oC, at constant pressure, till its volume increases by 10%. The specific heat of oxygen, under these conditions is 0.22 cal g – 1 K – 1. The amount of heat required (in joules) is

Q5

A drilling machine of power P watts is used to drill a hole in copper block of mass M kg. If the specific heat of a copper is s J  and 40% of  the power is lost due to heating of the machine, the rise in the temperature of the block in T seconds will be (in oC)

Q6

A geyser, operating on LPG (liquefied petroleum gas) heats water flowing at the rate of 3.0 litres per minute, from 27oC to 77oC. If the heat of combustion of LPG is , how much fuel in grams is consumed per minute?

Q7

A copper block of mass 2 kg is heated to a temperature of 500oC and then placed in a large block of ice at 0oC. What is the maximum amount of ice that can melt? The specific heat of copper is 400 j  and latent heat of fusion of water is .

Q8

The dimensions of the coefficient of thermal conductivity are

Q9

Two different metal rods of the same length have their ends kept at the same temperatures and  with . If A and are their cross-sectional areas and k1 and k2 their thermal conductivities, the rate of flow of heat in the two rods will be the same if

Q10

A one liter flask contains some mercury. It is found that at different temperatures the volume of air inside the flask remains the same. What is the volume of mercury in the flask? Given the coefficient of linear expansion of glass  oC–1, the coefficient of volume expansion of mercury is  oC–1.