# Conduction Law

## Trending Questions

**Q.**In a steady state of thermal conduction, temperature of the ends A and B of a 20 cm long rod are 100∘ C and 0∘ C respectively. What will be the temperature of the rod at a point at a distance of 6 cm from the end A of the rod

- None of the above

**Q.**A laboratory thermometer_____________.

- cannot measure temperatures below 0°C
- is generally used to measure the temperature of the human body
- can measure a temperature of 100°C
- has a kink near its bulb

**Q.**

Five rods of same dimensions are arranged as shown in the figure. They have thermal conductivities K1, K2, K3, K4 and K5. When points A and B are maintained at different temperatures, no heat flows through the central rod if

**Q.**Draw the diagram of a laboratory thermometer and label its parts. How does it differ from a clinical thermometer?

**Q.**The figure shows a system of two concentric spheres of radii r1 and r2 and kept at temperatures T1 and T2, respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to

**Q.**A composite block is made of slabs A, B, C, D and E of different thermal conductivities (given in terms of a constant K) and sizes (given in terms of length. L) as shown in the figure. All slabs are of same with. Heat Q flows only from left to right through the blocks. Then, in steady state

- heat flown trough A and E slabs are same
- heat flow through slab e is maximum
- temperature difference across slab E is smallest
- heat flow through C = heat flow through B + heat flow through D

**Q.**

An ice-box is made of wood 1.75 cm thick, lined inside with cork 2 cm thick. If the temperature of the inner surface of the cork is steady at 0°C and that of the outer surface is steady at 12∘C, what is the temperature of the interface? The thermal conductivity of wood is 5 times that of cork.

**Q.**

One end of a thermally insulated rod is kept at a temperature ${T}_{1}$ and the other at ${T}_{2}$. The rod is composed of two sections of lengths ${l}_{1}$ and ${l}_{2}$ and thermal conductivities ${k}_{1}$ and ${k}_{2}$ respectively as shown in the figure. The temperature at the interface of the two sections is :

**Q.**

A cylinder of radius R made of a material of thermal conductivity k, is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity k2. 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

**Q.**A body takes T minutes to cool from 62∘ C to61∘ C when the surrounding temperature is 30∘ C .The time taken by the body to cool from 46∘ C to 45.5∘ C is

- Greater than T minutes
- Equal to T minutes
- Equal to T/2 minutes
- Less than T minutes

**Q.**The length of mercury thread in a mercury thermometer is 2 mm at the ice point and 26 mm at the boiling point of water. What will be the length of the mercury thread in this thermometer if it is used to measure a temperature of 75 ℃?

**Q.**

A 5cm thick ice block is there on the surface of water in a lake. The temperature of air is −10∘ C; how much time it will take to double the thickness of the block

(L=80 cal/g, Kice=0.004 Erg/s−k, dice=0.92gcm−3)

- 1 hour
- 191 hours
- 19.1 hours
- 1.91 hours

**Q.**

One end of a copper rod of length 1.0 m and area of cross-section 10−3 is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is 92cal/m−s−∘C and the latent heat of ice is 8×104cal/kg, then the amount of ice which will melt in one minute is

**Q.**

A spherical ball A of surface area 20 cm2 is kept at the centre of a hollow spherical shell B of area 80 cm2. The surface of A and the inner surface of B emit as blackbodies. Assume that the thermal conductivity of the material of B is extremely poor and that of A is very high and that the air between A and B has been pumped out. The heat capacities of A and B are 42 J/∘C and 82 J/ ∘ C respectively. Initially the temperature of A is 100 ∘ C and that of B is 20 ∘ C.Find the rate of change of temperature of A and that of B at this instant.

0.05

^{0}c/s and 0.01^{0}c/s0.005

^{0}c/s and 0.0001^{0}c/s0.025

^{0}c/s and 0.0050^{0}c/s0.03

^{0}c/s and 0.01^{0}c/s

**Q.**

The thermal conductivity of a rod depends on

Length

Mass

Area of cross section

Material of the rod

**Q.**

Four rods of identical cross-sectional area and made from the same metal form the sides of square. The temperature of two diagonally opposite points is T and √2 T respective in the steady state. Assuming that only heat conduction takes place, what will be the temperature difference between the other two points

- 0
- None of these

**Q.**

Two slabs A and B of different materials but of the same thickness are joined as shown in the figure. The thermal conductivities of A and B are k1 and k2 respectively. The thermal conductivity of the composite slab will be

(k1+k2)

12(k1+k2)

√k1k2

2k1k2(k1+k2)

**Q.**

Two rods A and B of different materials are welded together as shown in Figure. If their thermal conductivities are k1and k2, the thermal conductivity of the composite rod will be

**Q.**The thermometer which is used to measure the temperature of human body is called as clinical thermometer.

- True
- False

**Q.**The thermometer which is used to measure the temperature of human body is called as clinical thermometer.

- True
- False

**Q.**Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 40 minutes respectively. The ratio of thermal conductivities of the materials is

- 5 : 6
- 6 : 5
- 3 : 1
- 2 : 1

**Q.**

Two cylindrical rods of lengths l1 and l2, radii r1 and r2 have thermal conductivities k1 and k2 respectively. The ends of the rods are maintained at the same temperature difference. If l1=2l2 and r1=r22, the rates of heat flow in them will be the same if k1k2 is

1

2

4

8

**Q.**If all the balls are identical except for difference in colours, arrange these balls in ascending order of their heat absorption capacity.

- II < I < III
- III < I < II
- III < II < I

- I < II < III

**Q.**A clinical thermometer cannot show _______ as its reading.

- 36°C
- 40°C
- 30°C
- 41°C

**Q.**A cylindrical aluminium rod of length 2m is maintained at a temperature difference of 10∘ Celsius. The radius of the rod is 1 cm. Find the heat current. (Thermal conductivity of aluminium = 200 W m−1 K−1.)

- 2.14 J/s
- 0.214 J/s
- 0.314 J/s
- 3.14 J/s

**Q.**

Two plates of the same area and the same thickness having thermal conductivities k1 and k2 are placed one on top of the other. The top and bottom faces of the composite plate are maintained at different constant temperatures. The thermal conductivity of the composite plate will be

(k1+k2)

k1k2(k1+k2)

2k1k2(k1+k2)

12(k1+k2)

**Q.**

Differentiate between convection and conduction? How is food cooked? [3 MARKS]

**Q.**A hot object with a temperature T1 is connected to a cool object with a temperature of T2. The object used to conduct heat has a length L and a cross-sectional area A. The rate of heat flow is :

- A(T1−T2)/kL
- k(T1−T2)/AL
- kAL/(T1−T2)
- kA(T1−T2)/L

**Q.**

A partition wall has two layers A and B in contact, each made of a different material. They have the same thickness but the thermal conductivity of layer A is twice that of layer B. If the steady state temperature difference across the wall is 60k, then the corresponding difference across the layer A is

- 10 K
- 20 K
- 30 K
- 40 K

**Q.**If the length of a minute hand of a wall clock is 7 cm, then the area swept by it in 30 minutes is cm2