Advertisements
Advertisements
प्रश्न
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?
Advertisements
उत्तर
Given:
Surface area of the spherical ball, SA = 20 cm2 = 20 × 10 -4 m-2
Surface area of the spherical shell, SB = 80 cm2 = 80 × 10-4 m2
Temperature of the spherical ball, TA = 300 K
Temperature of the spherical shell, TB = 300 K
Radiation energy emitted per second by the spherical ball A is given by
EA = σSATA4
⇒EA 6.0 ×10-8× 20 × 10-4 × (300)4
⇒EA = 0.97 J
Radiation energy emitted per second by the inner surface of the spherical shell B is given by
EB = σ SBTB4
⇒ EB = 6.0 ×10 -8 × 80 × 10-4 × (300)4
⇒ EB = 3.76 J ≈ 3.8 J
Energy emitted by the inner surface of B that falls back on its surface is given by
E = EB - EA = 3.76 - 0.94
⇒ E = 2.82 J
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
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?
Why is a white dress more comfortable than a dark dress in summer?
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
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 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 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?
According to Stefan–Boltzmann Law, if the temperature of a body is doubled (in Kelvin), the heat emitted by it becomes ______.
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?
Which of the following properties is shared by both thermal radiation and visible light?
