MODULE 5 - Radiation
The heat is transferred by conduction, convection and radiation in (A) Melting of ice (C) Condensation of steam in condenser (B) Boiler furnaces (D) None of these
B
. The time constant of a thermocouple is (A) The time taken to attain the final temperature to be measured (B) The time taken to attain 50% of the value of initial temperature difference (C) The time taken to attain 63.2% of the value of initial temperature difference (D) Determined by the time taken to reach 100°C from 0°C
C
According to Prevost theory of heat exchange (A) It is impossible to transfer heat from low temperature source to t high temperature source (B) Heat transfer by radiation requires no medium (C) All bodies above absolute zero emit radiation (D) Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
C
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in (A) Electric heater (C) Boiler (B) Steam condenser (D) Refrigerator condenser coils
C
Temperature of steam at around 540°C can be measured by (A) Thermometer (C) Thermocouple (B) Thermistor (D) None of these
C
The value of the wave length for maximum emissive power is given by (A) Kirchhoff's law (C) Wine's law (B) Stefan's law (D) Planck's law
C
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by (A) Conduction (C) Radiation (B) Convection (D) Conduction and convection
C
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the (A) Absolute temperature (C) Cube of the absolute temperature (B) Square of the absolute temperature (D) Fourth power of the absolute temperature
D
Heat transfer by radiation mainly depends upon (A) Its temperature (C) Kind and extent of its surface (B) Nature of the body (D) All of these
D
The radiation emitted by a black body is known as (A) Black radiation (C) Total radiation (B) Full radiation (D) All of these
D
The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as (A) Emissivity (C) Reflectivity (B) Transmissivity (D) Intensity of radiation
D
Which of the following is the case of heat transfer by radiation? (A) Blast furnace (C) Cooling of parts in furnace (B) Heating of building (D) Heat received by a person from fireplace
D
40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is (A) 0.45 (C) 0.40 (B) 0.55 (D) 0.75
a
According to Wien's law, the wavelength corresponding to maximum energy is proportion to (A) Absolute temperature (T) (C) F (B) I² (D) T
a
Depending on the radiating properties, a body will be black when (Where a = absorptivity, p = reflectivity, X = transmissivity.) (A) P = 0, x = 0 and a = 1 (C) P = 0, x = 1 and a = 0 (B) P= 1, T = 0 and a = 0 (D) X = 0, a + p = 0
a
The energy distribution of an ideal reflector at higher temperatures is largely in the range of (A) Shorter wavelength (C) Remain same at all wavelengths (B) Longer wavelength (D) Wavelength has nothing to do with it
a
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as (A) Kirchoff's law (C) Wien' law (B) Stefan's law (D) Planck's law
a
The ratio of the energy absorbed by the body to total energy falling on it is called (A) Absorptive power (C) Absorptivity (B) Emissive power (D) Emissivity
a
The value of the wavelength for maximum emissive power is given by (A) Wien's law (C) Stefan's law (B) Planck's law (D) Fourier's law
a
When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a (A) Black body (C) Opaque body (B) Grey body (D) White body
a
Depending on the radiating properties, a body will be white when (Where a = absorptivity, p = reflectivity, x = transmissivity) (A) P = 0, x = 0 and a = 1 (C) P = 0, x = 1 and a = 0 (B) P=1, T = 0 and a = 0 (D) X = 0, a + p = 1
b
Emissivity of a white polished body in comparison to a black body is (A) Higher (C) Same (B) Lower (D) Depends upon the shape of body
b
If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called (A) Absorptive power (C) Emissivity (B) Emissive power (D) None of these
b
Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium. (A) Cold body to hot body (C) Smaller body to larger body (B) Hot body to cold body (D) Larger body to smaller body
b
The expression Q = σ AT4 is called (A) Fourier equation (C) Newton Reichmann equation (B) Stefan-Boltzmann equation (D) Joseph-Stefan equation
b
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law. (A) Equal to (C) Inversely proportional to (B) Directly proportional to (D) None of these
b
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by (A) Convection (C) Forced convection (B) Radiation (D) Free convection
b
Which of the following statement is correct? (A) A grey body is one which absorbs all radiations incident on it. (B) At thermal equilibrium, the emissivity and absorptivity are same. (C) The energy absorbed by a body to the total energy falling on it, is called emissivity. (D) A perfect body is one which is black in color.
b
Wien's law states that the wave length corresponding to ________ is proportional to the absolute temperature. (A) Minimum energy (C) Both (A) and (B) (B) Maximum energy (D) None of these
b
19 Kirchhoff's law states that (A) The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature (B) The wave length corresponding to the maximum energy is proportional to the absolute temperature (C) The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body (D) None of the above
c
3. The automobile radiator is a heat exchanger of(A) Parallel flow type (C) Cross flow type (B) Counter flow type (D) Regenerator type
c
A grey body is one whose absorptivity (A) Varies with temperature (B) Varies with wavelength of the incident ray (C) Is equal to its emissivity (D) Does not vary with temperature and. wavelength of the incident ray
c
Absorptivity of a body will be equal to its emissivity (A) At all temperatures (C) When system is under thermal equilibrium (B) At one particular temperature (D) At critical temperature
c
According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to (A) Absolute temperature (C) Fourth power of absolute temperature (B) Square of temperature (D) Fourth power of temperature
c
Depending on the radiating properties, body will be transparent when (Where a = absorptivity, p = reflectivity, x = transmissivity) (A) P = 0, x = 0 and a = 1 (C) P = 0, T= 1, and a = 0 (B) P=1, x = 0, and a = 0 (D) X = 0, a + p = 1
c
Stefan Boltzmann law is applicable for heat transfer by (A) Conduction (C) Radiation (B) Convection (D) Conduction and radiation combined
c
The heat of sun reaches to us according to (A) Conduction (C) Radiation (B) Convection (D) None of these
c
The unit of Stefan-Boltzmann constant is (A) Watt/mK (C) Watt/m²K4 (B) Watt/m²K² (D) Watt/mK²
c
Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of (A) 1:1 (C) 1: 2 (B) 2: 1 (D) 4: 1
c
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be (A) One (C) Three (B) Two (D) Four
c
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as (A) Wien's law (C) Kirchhoff's law (B) Stefan's law (D) Planck's law
c
. The amount of radiation mainly depends upon the (A) Nature of the body (C) Type of surface of the body (B) Temperature of the body (D) All of these
d
56. A perfect black body is one which (A) Is black in color (B) Reflects all heat (C) Transmits all heat radiations (D) Absorbs heat radiations of all wave lengths falling on it
d
A grey body is one whose absorptivity (A) Varies with temperature (B) Varies with the wave length of incident ray (C) Varies with both (D) Does not vary with temperature and wave length of the incident ray
d
According of Kirchhoff's law (A) Radiant heat is proportional to fourth power of absolute temperature (B) Emissive power depends on temperature (C) Emissive power and absorptivity are constant for all bodies (D) Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body
d
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a (A) Grey body (C) Red hot body (B) Brilliant white polished body (D) Black body
d
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to (A) Absolute temperature (C) T⁵ (B) T² (D) T4
d
All radiations in a black body are (A) Reflected (C) Transmitted (B) Refracted (D) Absorbed
d
Depending on the radiating properties, a body will be opaque when (A) P = 0, x = 0 and a = 1 (C) P = 0, x = 1 and a = 0 (B) P=1, x = 0 and a = 0 (D) X = 0, a + p = 1
d
The amount of radiation mainly depends on (A) Nature of body (C) Type of surface of body (B) Temperature of body (D) All of the above
d
The emissive power of a body depends upon its (A) Temperature (C) Physical nature (B) Wave length (D) All of the above
d
The emissivity for a black body is (A) 0 (C) 0.75 (B) 0.5 (D) 1
d
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit (A) Temperature (C) Area (B) Thickness (D) Time
d
The unit of Stefan Boltzmann constant is (A) watt/cm² °K (C) watt²/cm °K⁴ (B) watt/cm⁴ °K (D) watt/cm² °K⁴
d
Total emissivity of polished silver compared to black body is (A) Same (C) More or less same (B) Higher (D) Very much lower
d
When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body, (A) α = 1, ρ = 0 and τ = 0 (C) α = 0, ρ = 0 and τ = 1 (B) α = 0, ρ = 1 and τ = 0 (D) α + ρ = 1 and τ = 0
d
