Advertisements
Advertisements
प्रश्न
A room has a window fitted with a single 1.0 m × 2.0 m glass of thickness 2 mm. (a) Calculate the rate of heat flow through the closed window when the temperature inside the room is 32°C and the outside is 40°C. (b) The glass is now replaced by two glasspanes, each having a thickness of 1 mm and separated by a distance of 1 mm. Calculate the rate of heat flow under the same conditions of temperature. Thermal conductivity of window glass = 1.0 J s−1 m−1°C−1 and that of air = 0.025 m-1°C-1 .
Advertisements
उत्तर
(a) 
Length, l = 2 mm = 0.0002 m
Rate of flow of heat `=(Delta"T")/(l/("KA"))`
`={1xx2xx(4032)}/{2xx10^-3}`
`={KA.DeltaT}/{l} `
`= {1xx2xx(40-32)}/{2xx10^-3}`
= 8000 J / sec
(b) 
|
Resistance of glass, `R_g = {l}/{K_g.A}`
Resistance of air, `R_A = {l}/{K_A.A}`
From the circuit diagram, we can find that all the resistors are connected
`R_s = R_g + R_A + R_g`
`=10^-3/2 (2/K_g + 1/K_A) `
`=10^-3 ( 2/1 + 1/0.025)`
`= 10^-3/2 xx((2xx0.025 + 1))/0.025`
Rate of flow of heat ,= `q ={DeltaT}/{R_5}`
`= ( T_1 - T_2)/R_s`
`= {(40-32) xx2xx0.025}/{40^_3xx(2xx0.025 + 1 )}`
=381W
APPEARS IN
संबंधित प्रश्न
Explain why a brass tumbler feels much colder than a wooden tray on a chilly day
A tightly closed metal lid of a glass bottle can be opened more easily if it is put in hot water for some time. Explain.
A metal sheet with a circular hole is heated. The hole
One end of a steel rod (K = 46 J s−1 m−1°C−1) of length 1.0 m is kept in ice at 0°C and the other end is kept in boiling water at 100°C. The area of cross section of the rod is 0.04 cm2. Assuming no heat loss to the atmosphere, find the mass of the ice melting per second. Latent heat of fusion of ice = 3.36 × 105 J kg−1.
A steel frame (K = 45 W m−1°C−1) of total length 60 cm and cross sectional area 0.20 cm2, forms three sides of a square. The free ends are maintained at 20°C and 40°C. Find the rate of heat flow through a cross section of the frame.
A cubical box of volume 216 cm3 is made up of 0.1 cm thick wood. The inside is heated electrically by a 100 W heater. It is found that the temperature difference between the inside and the outside surface is 5°C in steady state. Assuming that the entire electrical energy spent appears as heat, find the thermal conductivity of the material of the box.
Following Figure shows water in a container having 2.0 mm thick walls made of a material of thermal conductivity 0.50 W m−1°C−1. The container is kept in a melting-ice bath at 0°C. The total surface area in contact with water is 0.05 m2. A wheel is clamped inside the water and is coupled to a block of mass M as shown in the figure. As the block goes down, the wheel rotates. It is found that after some time a steady state is reached in which the block goes down with a constant speed of 10 cm s−1 and the temperature of the water remains constant at 1.0°C. Find the mass M of the block. Assume that the heat flows out of the water only through the walls in contact. Take g = 10 m s−2.
A semicircular rod is joined at its end to a straight rod of the same material and the same cross-sectional area. The straight rod forms a diameter of the other rod. The junctions are maintained at different temperatures. Find the ratio of the heat transferred through a cross section of the semicircular rod to the heat transferred through a cross section of the straight rod in a given time.
Consider the situation shown in the figure . The frame is made of the same material and has a uniform cross-sectional area everywhere. Calculate the amount of heat flowing per second through a cross section of the bent part if the total heat taken out per second from the end at 100°C is 130 J.
A calorimeter of negligible heat capacity contains 100 cc of water at 40°C. The water cools to 35°C in 5 minutes. The water is now replaced by K-oil of equal volume at 40°C. Find the time taken for the temperature to become 35°C under similar conditions. Specific heat capacities of water and K-oil are 4200 J kg−1 K−1 and 2100 J kg−1 K−1respectively. Density of K-oil = 800 kg m−3.
The coefficient of thermal conductivity depends upon ______.
Heat is associated with ______.
A thin rod having length L0 at 0°C and coefficient of linear expansion α has its two ends maintained at temperatures θ1 and θ2, respectively. Find its new length.
In conduction, how does heat mainly travel through a solid rod kept with one end in a flame?
Why are metals like copper and aluminium called good conductors of heat?
Which of the following is a correct example of a bad conductor of heat used in daily life to reduce heat loss or gain?
During conduction along a metal rod, which part becomes hot first, and why?
