Advertisements
Advertisements
प्रश्न
Calculate the amount of heat radiated per second by a body of surface area 12 cm2 kept in thermal equilibrium in a room at temperature 20°C. The emissivity of the surface = 0.80 and σ = 6.0 × 10−8 W m−2 K−4.
Advertisements
उत्तर
Given:
Area of the body, A = 12 × 10−4 m2 Temperature of the body, T = (273 + 20) = 293 K
Emissivity, e = 0.80
Rate of emission of heat, R = AeσT4
R = 12 × 10−4 × 0.80 × 6.0 × 10−8 × (293)4
R = 0.42 J (approximately)
APPEARS IN
संबंधित प्रश्न
Explain why the earth without its atmosphere would be inhospitably cold
Why does blowing over a spoonful of hot tea cools it? Does evaporation play a role? Does radiation play a role?
Standing in the sun is more pleasant on a cold winter day than standing in shade. Is the temperature of air in the sun considerably higher than that of the air in shade?
A solid at temperature T1 is kept in an evacuated chamber at temperature T2 > T1. The rate of increase of temperature of the body is proportional to
Two bodies A and B having equal surface areas are maintained at temperature 10°C and 20°C. The thermal radiation emitted in a given time by A and B are in the ratio
A solid sphere and a hollow sphere of the same material and of equal radii are heated to the same temperature.
(a) Both will emit equal amount of radiation per unit time in the biginning
(b) Both will absorb equal amount of radiation from the surrounding in the biginning.
(c) The initial rate of cooling (dT/dt) will be the same for the two spheres
(d) The two spheres will have equal temperature at any instant
The left end of a copper rod (length = 20 cm, area of cross section = 0.20 cm2) is maintained at 20°C and the right end is maintained at 80°C. Neglecting any loss of heat through radiation, find (a) the temperature at a point 11 cm from the left end and (b) the heat current through the rod. Thermal conductivity of copper = 385 W m−1°C−1.
Assume that the total surface area of a human body is 1.6 m2 and that it radiates like an ideal radiator. Calculate the amount of energy radiated per second by the body if the body temperature is 37°C. Stefan constant σ is 6.0 × 10−8 W m−2 K−4.
A cylindrical rod of length 50 cm and cross sectional area 1 cm2 is fitted between a large ice chamber at 0°C and an evacuated chamber maintained at 27°C as shown in the figure. Only small portions of the rod are inside the chamber and the rest is thermally insulated from the surrounding. The cross section going into the evacuated chamber is blackened so that it completely absorbs any radiation falling on it. The temperature of the blackened end is 17°C when steady state is reached. Stefan constant σ = 6 × 10−8 W m−2 K−4. Find the thermal conductivity of the material of the rod.
You place your hands near a burning candle and feel warmth on both sides of the flame. What does this observation mainly show?
Which statement best describes thermal radiation from everyday objects like trees, roads, and buildings at night?
Two identical metal tins with water are kept in sunlight. One is black and the other shiny. Why does water in the black tin become hotter?
Why are cooking utensils like pans made of metal but fitted with plastic or wooden handles?
According to Stefan–Boltzmann Law, if the temperature of a body is doubled (in Kelvin), the heat emitted by it becomes ______.
A perfect black body has an emissivity value of ______.
In the experiment where a test tube of water is heated from the top with ice at the bottom, the ice does not melt. What is the primary reason for this?
