In thermal radiation for a black body (where, ε is emissivity and α is
absorptivity)
(A) α = 1; ε ≠ 1
(B) α ≠ 1, ε = 1
(C) α ≠ 1, ε ≠ 1
(D) α = 1; ε = 1
Description : What refers to the rate of thermal radiation emitter per unit area of a body? A. Thermal conductivity B. Absorptivity C. Emissivity D. Emissive power
Last Answer : Emissive power
Description : The absorptivity of a body is equal to its emissivity (A) At a particular temperature (B) For circular bodies (C) Under thermal equilibrium (D) None of these
Last Answer : (C) Under thermal equilibrium
Description : For an ideal black body (A) Absorptivity = 1 (B) Reflectivity = 1 (C) Emissivity = 0 (D) Transmissivity = 1
Last Answer : (A) Absorptivity = 1
Description : Define the following terms : (i) absorptivity (ii) reflectivity (iii) transmissivity (iv) emissivity
Last Answer : Absorptivity: It is the fraction of total incident radiation which is absorbed by a body. Reflectivity: It is the fraction of total incident radiation which is reflected by a body. Transmissivity: It ... total emissive power of a body to emissive power of a black body at the same temperature.
Description : reduction in thermal resistance during heat transfer does not occur in the (A) Convection heat transfer by stirring the fluid and cleaning the heating surface (B) Conduction heat transfer by ... Radiation heat transfer by increasing the temperature and reducing the emissivity (D) None of these
Last Answer : Option C
Description : Which of the following equations as suggested by Colebrook and White gives the increase in roughness of a new surface (ε0 ) with age/time (t) (where, ε = roughness of the surface after time't'. α = a co-efficient to be experimentally determined ... ε = ε0 + α.t 2 (C) ε = ε0 + α.t 3 (D) ε = ε0 + α.t
Last Answer : (A) ε = ε0 + α.t
Description : The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoff’s law. (A) Wavelength of radiation (B) Nature of the body (C) Temperature of the body (D) None of these
Last Answer : (C) Temperature of the body
Description : The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation. (A) Increases (B) Decreases (C) Remain constant (D) May increase or decrease; depends on the material
Last Answer : (D) May increase or decrease; depends on the material
Description : The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by (A) Painting the surface black (B) ... white (with aluminium paint) (C) Giving the surface a mirror finish (D) Roughening the surface
Last Answer : (B) Painting the surface white (with aluminium paint)
Description : A __________ surface has the maximum thermal emissivity out of the following. (A) Black & smooth (B) Black & rough (C) White & smooth (D) White & rough
Last Answer : (B) Black & rough
Description : For infinite parallel planes having emissivities ε1 & ε2, the interchange factor for radiation from surface 1 to surface 2 is given by (A) (ε1 + ε2)/ε1.ε2 (B) ε1.ε2/(ε1 + ε2 - ε1.ε2) (C) ε1.ε2 (D) ε1 + ε
Last Answer : Option B
Description : Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity? (A) Aluminium foil (B) Refractory bricks (C) Iron plate (D) Coke breeze
Last Answer : (D) Coke breeze
Description : What is the absorptivity of a black body? (A) 1 (B) 0 (C) 0.78 (D) 0.95
Last Answer : (A) 1
Description : Pick out the wrong statement: (A) With change in temperature, the radiant energy emitted by a black body remains unchanged (B) Absorptivity of a body approaches unity in case of diffuse reflection (C) Absorptivity of ... unity (D) Value of Stefan-Boltzmann constant is 4.876 10 -8 KCal/m2 .hr.°K4
Last Answer : (A) With change in temperature, the radiant energy emitted by a black body remains unchanged
Description : Absorptivity and reflectivity of a perfect black body are respectively (A) 1 and 0 (B) 0 and 1 (C) 1 and ∞ (D) 0 and 0.5
Last Answer : (A) 1 and 0
Description : Tar is a better fuel than furnace oil, because of its (A) Higher calorific value (B) Lower sulphur content (C) Higher emissivity (0.8-0.9) resulting in higher radiation heat transfer rate (D) Both (A) and (B)
Last Answer : (D) Both (A) and (B)
Description : What states that for any two bodies in thermal equilibrium, the ratios of emissive power to the absorptivity are equal? A. Kirchhoff’s radiation law B. Newton’s law of cooling C. Stefan-Boltzmann law D. Hess’s law
Last Answer : Kirchhoff’s radiation law
Description : The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2 . The approximate surface temperature (K) is (Stefan-Boltzmann constant = 5.67 × 10 -8 W/m2 .K4 ) (A) 1000 (B) 727 (C) 800 (D) 1200
Last Answer : (A) 1000
Description : Thickness of stock does not affect the fuel economy of furnaces, if thematerial to be heated is of (A) Low emissivity (B) High thermal conductivity (C) Both (A) and (B) (D) Neither (A) nor (B)
Last Answer : (C) Both (A) and (B)
Description : In a furnace, the heat taken by the charge/stock and the heat lost to the furnace structure & flue gases depends on the (A) Rate of firing and emissivity of flame (B) Thermal conductivity of the charge & ... (C) Nature of process; whether batch, continuous or intermittent (D) All (A), (B) and (C)
Last Answer : (D) All (A), (B) and (C)
Description : What is the absorptivity of a black body? A. 0 B. 1 C. 0.5 D. 0.25
Last Answer : 1
Description : While the total emissivity of a perfect black body is unity, the same for a real body is (A) 0 (B) 1 (C) > 1 (D) Between 0 and 1
Last Answer : (D) Between 0 and 1
Description : What is the emissivity of a black body? (A) 0 (B) 1 (C) 0.5 (D) 0.90
Last Answer : (B) 1
Description : Calculate the rate of heat transfer by radiation from an unlagged steam pipe, 50 mm o.d. at 393K to air at 293K emissivity e = 0.9.
Last Answer : Rate of heat transfer by radiation Assume length of pipe = 1 m
Description : The thermal radiation emitted by a body is proportional to T n , where T is its absolute temperature. The value of 'n' is exactly 4 for (A) Black painted bodies only (B) All bodies (C) Polished bodies only (D) A black body
Last Answer : (B) All bodies
Description : What is the emissivity of a black body? A. 0 B. 1 C. 0.5 D. 0.25
Description : The sum of reflectivity and absorptivity for an opaque body is equal to (A) 0.5 (B) 1 (C) 0 (D) 2
Description : When the liquid over a plate is of uniform concentration, then (A) Murphree efficiency > point efficiency (B) Murphree efficiency < point efficiency (C) Murphree efficiency = point efficiency (D) Murphree efficiency ≠ point efficiency
Last Answer : (C) Murphree efficiency = point efficiency
Description : High pressure steam is expanded adiabatically and reversibly through a well insulated turbine, which produces some shaft work. If the enthalpy change and entropy change across the turbine are represented by ΔH and ΔS respectively for this process: ... (C) Δ H ≠ 0 and ΔS ≠ 0 (D) Δ H = 0 and ΔS ≠ 0
Last Answer : (B) Δ H ≠ 0 and ΔS = 0
Description : Maximum amount of thermal radiation is emitted at all wavelengths at any specified temperature by a/an __________ body. (A) Grey (B) Black (C) Opaque
Last Answer : (A) Grey
Description : The thermal radiation emitted by a blackbody heated to a given temperature. a. Gamma Radiation b. Black Body Radiation c. Electromagnetic Radiation d. Alpha Radiation
Last Answer : Black Body Radiation
Description : Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be (A) 0.35 (B) 0.45 (C) 0.55 (D) 0.85
Last Answer : (B) 0.45
Description : A body is called grey if the monochromatic emissivity of the body is (A) Zero (B) Unity (C) Same for all wavelengths (D) Different for all wavelengths
Last Answer : (C) Same for all wavelengths
Description : When ≠ , the absorber is known as A. Untuned vibration absorber B. Tuned vibration absorber C. Both of above D. None of these
Last Answer : A. Untuned vibration absorber
Description : The value(s) of 'k' for which the following pair of linear equations will represent a pair of intersecting lines graphically is/are: 3x - 4y + 7 = 0 kx - 8y = 5 (a) k = 6 (b) k ≠ 6(c) any real number (d) any real number except 6
Last Answer : (d) any real number except 6
Description : The grammar with production rules S → aSb |SS|λ generates language L given by: (A) L = {w∈{a, b}* | na(w) = nb(w) and na(v) ≥ nb(v) where v is any prefix of w} (B) L = {w∈{a, b}* | na(w) = nb(w) and na(v ... (D) L = {w∈{a, b}* | na(w) ≠ nb(w) and na(v) ≤ nb(v) where v is any prefix of w}
Last Answer : (A) L = {w∈{a, b}* | na(w) = nb(w) and na(v) ≥ nb(v) where v is any prefix of w}
Description : A set of processors P1, P2, ......, Pk can execute in parallel if Bernstein's conditions are satisfied on a pair wise basis; that is P1 || P2 || P3 || ..... || Pk if and only if: (A) Pi || Pj for all i ≠ j (B) Pi || Pj for all i = j+1 (C) Pi || Pj for all i ≤ j (D) Pi || Pj for all i ≥ j
Last Answer : (A) Pi || Pj for all i ≠ j Explanation: Bernstein's Condition: 1. If process Pi writes to a memory cell Mi, then no process Pj can read the cell Mi. 2. If process Pi read from a memory ... Mi. 3. If process Pi writes to a memory cell Mi, then no process Pj can write to the cell Mi.
Description : Colebrook equation for friction factor in turbulent flow is given by, f -0.5 = -4 loge [(ε/D) + (1.26/NRe √F). It reduces to Nikuradse equation for a value of (ϵ/D) equal to (A) 0 (B) 1 (C) ∞ (D) 0.5
Description : For a perfectly transparent surface (like gases), the (A) Absorptivity = 0 (B) Transmissivity = 1 (C) Reflectivity = 0
Last Answer : (B) Transmissivity = 1
Description : Which of the following has the minimum absorptivity? (A) Aluminium foil (B) Coal dust (C) Refractory bricks (D) Iron plates
Last Answer : (A) Aluminium foil
Description : The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium". This is __________ law. (A) Kirchoff’s (B) Planck's (C) Wien's displacement (D) Stefan-Boltzmann
Last Answer : (A) Kirchoff’s
Description : In fluid flow, and heat and mass transfer, one encounters (i) kinematic velocity (μ), (ii) molecular diffusivity (θ) and thermal diffusivity (α). The units of these quantities are. (A) μ , α and θ all have units of m/ ... μ has unit of m/s (D) α and θ have units of m/s, while μ has unit of m2/s
Description : What is a body that emits a constant emissivity regardless of the wavelength? A. Gray body B. Black body C. Real body D. White body
Last Answer : Gray body
Description : Termination of the synthesis of the RNA molecule is signaled by a sequence in the template strand of the DNA molecule, a signal that is recognized by a termination protein, the (A) Rho (ρ) factor (B) σ factor (C) δ factor (D) ε factor
Last Answer : Answer : A
Description : Type ε H chain is present in (A) Ig A (B) Ig M (C) Ig D (D) Ig E
Last Answer : Answer : D
Description : Damping factor, ε = A. C/Cc B. C.Cc C. K/m D. K.m
Last Answer : A. C/Cc
Description : The expression for intrinsic impedance is given by a) √(με) b) (με) c) √(μ/ε) d) (μ/ε)
Last Answer : c) √(μ/ε)
Description : The relation between the speed of light, permeability and permittivity is a) C = 1/√(με) b) C = με c) C = μ/ε d) C = 1/με
Last Answer : a) C = 1/√(με)
Description : The expression for the loss tangent is given by a) σ/ωε b) ωε/σ c) σ/ω d) ω/ε
Last Answer : a) σ/ωε
Description : Which of the following relation will hold good? a) D = μ H b) B = ε E c) E = ε D d) B = μ H
Last Answer : d) B = μ H