Conduction

IMPORTANT

Conduction: Overview

This topic covers concepts such as The Steady State Heat Flow, Heat Flow and Area of Cross Section, Coefficient of Thermal Conductivity, Heat Flow through Slabs in Series, Heat Flow through Slabs in Parallel, Wiedemann-Franz law, etc.

Important Questions on Conduction

MEDIUM
IMPORTANT

A metal rod of length 2 m has cross sectional areas 2A and A as shown in the figure. The ends are maintained at temperatures 100°C and 70°C. The temperature at middle point C is___°C.

Question Image

EASY
IMPORTANT

Which of these quantities does Weidemann-Franz law connect?

(i) Thermal conductivity
(ii) Electrical conductivity
(iii) Specific heat

EASY
IMPORTANT

For thermal conductivity k, electrical conductivity σ, temperature T and Lorenz number L, which one of the following is the correct equation for Weidemann-Franz law?

EASY
IMPORTANT

For a long hollow cylinder maintained at uniform but different temperatures from its inner core to the outer surface, transfer of heat may be assumed to be taking place in which direction?

EASY
IMPORTANT

Which one of the following is correct for steady-state heat transfer in a conductor?

Here, Q is the heat energy transferred
And t is time

EASY
IMPORTANT

One end of a uniform conductor of length 50 cm and cross-sectional area 10 cm2 is placed at freezing point and the other end is placed at the boiling point of water. If the material of this conductor has a thermal conductivity of 50 W m-1 K-1, calculate the rate of heat energy transfer from the hot end to the cold end in the unit of kW.

EASY
IMPORTANT

Explain why does the temperature of a pan placed on a stove becomes constant after heating it for a while.

EASY
IMPORTANT

Wiedemann-Franz law shows that with the increase in velocity of particles inside a conductor, its thermal conductivity decreases and electrical conductivity increases.

EASY
IMPORTANT

During steady state, the flow of heat depends only on _______ of the conductor.

EASY
IMPORTANT

Thermometric conductivity describes how fast heat can transfer from a hot body to a cold body whereas thermal conductivity describes how well a material can spread heat.

EASY
IMPORTANT

Which one of the following is the correct SI unit for thermometric conductivity? 

HARD
IMPORTANT

One end of a copper rod of length 1.0 m and area of cross-section 10-3 m2 is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is 92 cal /m-s-C and the latent heat of ice is 8×104cal/kg,then the amount of ice which will melt (in grams) in one minute is

MEDIUM
IMPORTANT

A copper rod of length 2.5 m and an iron rod of length 1.5 m having the same areas of cross section are connected in series. Thermal conductivities of copper and iron are respectively 400 and 80 SI units. The equivalent conductivity of the composite bar in SI unit is ____.

MEDIUM
IMPORTANT

Heat is passed through two cylindrical rods of same material. Their diameters and lengths are in the ratio 1:2 and 2:1 respectively. If their ends are maintained at same temperature difference, the ratio of rate of flow of heat through them is

HARD
IMPORTANT

A long rod has one end at 0°C and other end at a high temperature. The coefficient of thermal conductivity varies with distance x from the low temperature end as, k=k01+ax, where k0=102 SI unit and a=1 m-1. At what distance from the first end, the temperature will be 100°C? The area of cross-section is 1 cm2 and rate of heat conduction is 1 W.

HARD
IMPORTANT

What is the rate of flow of heat through a tapering rod of length tapering from radius r1 and r2, when the temperature of the ends are θ1°C and θ2C and coefficient of thermal conductivity is K?

MEDIUM
IMPORTANT

An icebox almost completely filled with ice at 0°C is dipped into a large volume of water at 20°C. The box has walls of surface area 2400 cm2, thickness 2.0 mm and thermal conductivity 0.06W m1°C1. Calculate the rate at which the ice melts in the box. Latent heat of fusion of ice =3.4×105 J kg1.

HARD
IMPORTANT

Water is boiled in a container having a bottom of surface area 25 cm2, thickness 1.0 mm and thermal conductivity 50 W m1°C1. 100 g of water is converted into steam per minute in the steady-state after the boiling starts. Assuming that no heat is lost to the atmosphere, calculate the temperature of the lower surface of the bottom. Latent heat of vaporization of water =2.26×106 J kg1.

MEDIUM
IMPORTANT

The normal body-temperature of a person is 97°F. Calculate the rate at which heat is flowing out of his body through the clothes assuming the following values. Room temperature  =47°F, surface of the body under clothes =1.6 m2, conductivity of the cloth=0.04J s1m1°C1, thickness of the cloth =0.5 cm

MEDIUM
IMPORTANT

A liquid-nitrogen container is made of a1 cm  thick styrofoam sheet having thermal conductivity 0.025 J s1m1°C1. Liquid nitrogen at 80 K is kept in it. A total area of 0.80 m2 is in contact with the liquid nitrogen. The atmospheric temperature is 300 K . Calculate the rate of heat flow from the atmosphere to the liquid nitrogen.