Advertisements
Advertisements
प्रश्न
Cloudy nights are warmer than the nights with clean sky. Explain
Advertisements
उत्तर
During night, the earth's surface radiates infrared radiation of larger wavelength. Gas molecules in the air absorb some of this energy and radiate energy of their own in all directions. Also, water molecules, like the vapour that makes the clouds, absorb more frequencies of infrared energy than clear air does.
Both these factors contribute to the fact that clouds radiate more heat in all directions (including the earth) than clear air does. In turn, this makes the overall temperature on the earth warmer when there is a cloud cover. The heat energy radiated by the earth is reflected back to earth. Due to this, cloudy nights are warmer than the nights with clean sky.
APPEARS IN
संबंधित प्रश्न
Explain why an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open but gives a correct value for the temperature when the same piece is in the furnace
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
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 solid aluminium sphere and a solid copper sphere of twice the radius are heated to the same temperature and are allowed to cool under identically surrounding temperatures. Assume that the emissivity of both the spheres in the same. Find the ratio of (a) the rate of heat loss from the aluminium sphere to the rate of heat loss from the copper sphere and (b) the rate of fall of temperature of the aluminium sphere to the rate of fall of temperature of the copper sphere. The specific heat capacity of aluminium = 900 J kg−1°C−1 and that of copper = 390 J kg−1°C−1. The density of copper = 3.4 times the density of aluminium.
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. Both A and B are at 300 K. (a) How much is the radiation energy emitted per second by the ball A? (b) How much is the radiation energy emitted per second by the inner surface of B? (c) How much of the energy emitted by the inner surface of B falls back on this surface itself?
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.
A student says, "Heat from the Sun reaches Earth because air carries it across space." Which statement best explains why this is incorrect?
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?
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 ______.
Thermal radiation is described as a two-step process. Which of the following correctly identifies both steps in the correct order?
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?
