Advertisements
Advertisements
Question
The heat current is written as `(ΔQ)/(Δt)`. Why don't we write `(dQ)/dt?`
Solution
The amount of heat crossing through any cross-section of a slab in time `Δt` is called heat current.
It is written as `(ΔQ)/(Δt)` and not `(ΔQ)/(Δt)` as complete derivative . This is because the amount of heat crossing through any cross section is a function of many variables like temperature difference, area of cross-section, etc. So, we cannot write it as a complete derivative with respect to time.
APPEARS IN
RELATED QUESTIONS
Draw a neat labelled diagram for Ferry's perfectly black body.
Let 'p' and 'E' denote the linear momentum and energy of emitted photon respectively. If the wavelength of incident radiation is increased ___ .
(a) both p and E increase
(b) p increases and E decreases
(c) p decreases and E increases
(d) both p and E decrease.
Show graphical representation of energy distribution spectrum of perfectly black body.
The wavelength range of thermal radiation is
(A) from 4000 Å to 7000 Å
(B) from 7700 Å to 4 x 106 Å
(C) from 106 Å to 108 Å
(D) from 4 x 10-12 Å to 4 x 108 Å
When electron in hydrogen atom jumps from second orbit to first orbit, the wavelength of radiation emitted is λ. When electron jumps from third orbit to first orbit, the wavelength of emitted radiation would be _______.
(A)`27/32lambda`
(B)`32/27lambda`
(C)`2/3lambda`
(D)`3/2lambda`
Find the wavelength at which a black body radiates maximum energy, if its temperature is 427°C.
(Wein’s constant b = 2.898 × 10-3 mK)
(A) 0.0414 × 10-6m
(B) 4.14 × 10-6m
(C) 41.4 × 10-6m
(D) 414 × 10-6m
Explain black body radiation spectrum in terms of wavelength
What is perfectly black body ? Explain Ferry’s black body.
Does a body at 20°C radiate in a room, where the room temperature is 30°C? If yes, why does its temperature not fall further?
A blackbody does not
(a) emit radiation
(b) absorb radiation
(c) reflect radiation
(d) refract radiation
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 = 0.04 J s−1 m−1°C−1, thickness of the cloth = 0.5 cm.
A copper sphere is suspended in an evacuated chamber maintained at 300 K. The sphere is maintained at a constant temperature of 500 K by heating it electrically. A total of 210 W of electric power is needed to do it. When the surface of the copper sphere is completely blackened, 700 W is needed to maintain the same temperature of the sphere. Calculate the emissivity of copper.
A body cools down from 50°C to 45°C in 5 mintues and to 40°C in another 8 minutes. Find the temperature of the surrounding.
A metal ball of mass 1 kg is heated by means of a 20 W heater in a room at 20°C. The temperature of the ball becomes steady at 50°C. (a) Find the rate of loss of heat to the surrounding when the ball is at 50°C. (b) Assuming Newton's law of cooling, calculate the rate of loss of heat to the surrounding when the ball rises 30°C. (c) Assume that the temperature of the ball rises uniformly from 20°C to 30°C in 5 minutes. Find the total loss of heat to the surrounding during this period. (d) Calculate the specific heat capacity of the metal.
A hot body placed in a surrounding of temperature θ0 obeys Newton's law of cooling `(d theta)/(dt) = -K(theta - theta_0)` . Its temperature at t = 0 is θ1. The specific heat capacity of the body is sand its mass is m. Find (a) the maximum heat that the body can lose and (b) the time starting from t = 0 in which it will lose 90% of this maximum heat.
Which of the following is an example of an ideal black body?
Which of the following series of transitions in the spectrum of hydrogen atom falls in visible region?
