InterviewSolution
Saved Bookmarks
InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
The graph, shown in the adjacent diagram, represents the variation of temperature (T) of two bodies, x and y having same surface area, with time (t) due to the emission of radiation. Find the correct relation between the emissivity and absorptivity power of the two bodies A. `e_(x)gtE_(y)` and `a_(x)lta_(y)`B. `e_(x)ltE_(y)` and `a_(x)gta_(y)`C. `e_(x)gtE_(y)` and `a_(x)gta_(y)`D. `e_(x)ltE_(y)` and `a_(x)lta_(y)` |
| Answer» Correct Answer - C | |
| 52. |
By which of the following methods could a cup of hot tea loss heat when placed on metallic table in a class room .A. a,bB. b,cC. a,b,cD. a,b,c,d |
| Answer» Correct Answer - D | |
| 53. |
In which of the following process, convection does not take place primarily |
| Answer» Correct Answer - C | |
| 54. |
In which of the following process, convection does not take place primarilyA. Sea and Land breezeB. Boiling of waterC. Warming of glass of bulb due to filamnetD. Heating of air around a furance |
| Answer» Correct Answer - C | |
| 55. |
A bucket full of hot water cools from `75^(@)C` to `70^(@)C` in time `T_(1)`, from `70^(@)C` to `65^(@)C` in time `T_(2)` and from `65^(@)C` to `60^(@)C` in time `T_(3)`, thenA. `T_(1) = T_(2) = T_(3)`B. `T_(1) gt T_(2) gt T_(3)`C. `T_(1) lt T_(2) lt T_(3)`D. `T_(1) gt T_(2) gt T_(3)` |
|
Answer» Correct Answer - C |
|
| 56. |
A vessel full of hot water is kept in a room and it cools from `80^(@)C` to `75^(@)C` in `T_(1)` minutes, from `75^(@)C` to `70^(@)C` in `T_(2)` minutes and from `70^(@)C` to `65^(@)C` in `T_(3)` minutes Then .A. `T_(1) =T_(2) =T_(3)`B. `T_(1) gt T_(2) gtT_(3)`C. `T_(1)ltT_(2)=T_(3)`D. `T_(1) lt T_(2) lt T_(3)` |
|
Answer» Correct Answer - D Rate cooling decreases with fall of temperature Hence, time increases . |
|
| 57. |
If the rate of emission of radiation by a body at temperature `TK` is `E` then graph between log `E` and log `T` will be .A. B. C. D. |
|
Answer» Correct Answer - A Use `E = eA sigma T^(4)` apply log on both sides . |
|
| 58. |
According to ‘Newton’s Law of cooling’, the rate of cooling of a body is proportional to theA. Temperature of the bodyB. Temperature of the surroundingC. Fourth power of the temperature of the bodyD. Difference of the temperature of the body and the surroundings |
|
Answer» Correct Answer - D |
|
| 59. |
It takes `10 minutes` to cool a liquid from `61^(@)C` to `59^(@)C`. If room temperature is `30^(@)C` then find the time taken in cooling from `51^(@)C` to `49^(@)C`.A. 10 minB. 11 minC. 13 minD. 15 min |
|
Answer» Correct Answer - D |
|
| 60. |
In a room where the temperature is `30^(@)C`, a body cools from `61^(@)C` to `59^(@)C` in 4 minutes. The time (in min.) taken by the body to cool from `51^(@)C` to `49^(@)C` will beA. 4 minB. 6 minC. 5 minD. 8 min |
|
Answer» Correct Answer - B |
|
| 61. |
A body cools in 7 minutes from `60^(@)C` to `40^(@)C` What time (in minutes) does it take to cool from `40^(@)C` to `28^(@)C` if the surrounding temperature is `10^(@)C` ? Assume Newton’s Law of cooling holdsA. 3.5B. 11C. 7D. 10 |
|
Answer» Correct Answer - C |
|
| 62. |
A body takes T minutes to cool from `62^@C` to `61^@C` when the surrounding temperature is `30^@C`. The time taken by the body to cool from `46^@C` to `45.5^@C` isA. Greater than T minutesB. Equal to T minutesC. Less than T minutesD. Equal to T/2 minutes |
|
Answer» Correct Answer - B |
|
| 63. |
Themperature of a body `theta` is slightly more than the temperature of the surrounding `theta_(0)` its rate of cooling `(R )` versus temperature of body `(theta)` is plotted its shape would be .A. B. C. D. |
| Answer» Correct Answer - B | |
| 64. |
Two identical rods are connected between two containers. One of them is at `100^(@)C` containing water and another is at `0^(@)C` containing ice. If rods are connected in parallel then the rate of melting of ice is `q_(1)g//s` . If they are connected in series then teh rate is `q_(2)g//s` . The ratio `q_(2)//q_(1)` is |
|
Answer» Correct Answer - 4 `("Temperature difference")/("Thermalresistance")=L((dm)/(dt))` `(dm)/(dt)prop(1)/("Thermalresistance"),qprop(1/(R))` The rods are in parallel in the first case and they are in series in the second case `(q_(1))/(q_(2))=(2R)/((R//2))=4` . |
|
| 65. |
A heated body emits radiation which has maximum intensity at frequency `v_m` If the temperature of the body is doubled:A. the maximum intensity radiation will be at frequency `2v_(m)`B. the maximum intensity radiation will be at frequency `(1//2)v_(m)`C. the total emitted energy will increase by a factor16D. the total emitted energy will increase by a factor 2 |
|
Answer» Correct Answer - `(A,C)` |
|
| 66. |
The intensity of radiation emitted by the sun has its maximum value at a wavelength of 510 nm and that emitted by the North star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperatures of the sun and the north star is |
|
Answer» Correct Answer - `0.69` |
|
| 67. |
A very small hole in an electric furnace is used for heating metals. The hole nearly acts as black body. The area of the hole is `200mm^(2)` To keep a metal at `727^(@)C` heat energy flowing throungh this hole per sec in joules is `(sigam =5.67 xx 10^(-8)Wm^(-2)K^(-4))` .A. `22.68`B. `2.268`C. `1.134`D. `11.34` |
|
Answer» Correct Answer - D `P =sigmaAT^(4)` |
|
| 68. |
Relation between emissivity e and absorptive power a is (for black body)A. `e = a`B. `e = (1)/(a)`C. `e = a^(2)`D. `a = e^(2)` |
|
Answer» Correct Answer - A |
|
| 69. |
The area of a hole of heat furnace is `10^(-4)m^(2)`. It radiates `1.58xx10^(5)` calories of heat per hour. If the emissivity of the furnace is 0.80, then its temperature isA. 1500 KB. 2000 KC. 2500 KD. 3000 K |
|
Answer» Correct Answer - C |
|
| 70. |
A metal ball of surface area `200 cm^(2)` and temperature `527^(@)C` is surrounded by a vessel at `27^(@)C` . If the emissivity of the metal is 0.4, then the rate of loss of heat from the ball is `(sigma = 5.67 xx10^(-8)J//m^(2)-s-k^(4))`A. 108 joules approx.B. 168 joules approx.C. 182 joules approx.D. 192 joules approx. |
|
Answer» Correct Answer - C |
|
| 71. |
Assertion : Animals curl into a ball, when they feel very cold. Reason : Animals by curling their body reduces the surface area.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertionC. If assertion is true reason is falseD. If the assertion and reason both are false. |
|
Answer» Correct Answer - A |
|
| 72. |
On a cold morning, a metal surface will feel colder to touch than a wooden surface becauseA. Metal has high specific heatB. Metal has high thermal conductivityC. Metal has low specific heatD. Metal has low thermal conductivity |
|
Answer» Correct Answer - B |
|
| 73. |
At a common temperature, a block of wood and a block of metal feel equally cold or hot. The temperatures of block of wood and block of metal areA. Equal to temperature of the bodyB. Less than the temperature of the bodyC. Greater than temperature of the bodyD. Either (b) or (c) |
|
Answer» Correct Answer - A |
|
| 74. |
The two ends of a metal rod are maintained at temperatures `100^(@)C` and `110^(@)C` . The rate of heat flow in the rod is found to be `4.0 j//s`. If the ends are maintaind at temperatures `200^(@)C` and `210^(@)C`, the rate of heat flow will be :A. `0.6W`B. `0.9W`C. `1.6 W`D. `1.8W` |
|
Answer» Correct Answer - C R =Total thermal resistance of the ring `DeltaT` = difference in temperature between `A` and `B` for `theta =180^(@)` equivalent resistance between `A` and `B` is `R//2 & R//2` in parallel Rate of flow of heat `I_(1) = 1.2 = (DeltaT)/(R//4) :. (DeltaT)/(R) =0.3` For `theta =90^(@)` equivalent resistance between `A` & `B` is `3R//16` (`R //4` and `3R//4` in parallel) Rate of flow of heat `I_(2) = (DeltaT)/(3R//16) = (16)/(3) xx 0.3 =1.6W` . |
|
| 75. |
Three metal rods of coefficient of thermal conductivities `K,2K,3K` conducts heats of `3Q, 2Q,Q` per seconds through unit area then the ratio of temperature gradients .A. `9:3:1`B. `9:1:1`C. `3:1:1`D. `1:1:1` |
|
Answer» Correct Answer - A `Q=(KA(Deltatheta)t)/(l)` `((Deltatheta)/(l))prop(Q)/(K)"let"(Deltatheta)/(l)=XrArrXprop(Q)/(K)` `X_(1) :X_(2):X_(3)=(Q_(1))/(K_(1)):(Q_(2))/(K_(2)):(Q_(3))/(K_(3))` . |
|
| 76. |
Two rods one is semi circular of thermal conductivity `K_(1)` and otheir is straight of thermal conductivity `K_(2)` and of same cross sectional area are joined as shown in the The points `A` and `B` are maintained at same temperature difference. If rate of flow of heat is same in two rods then `K_(1)//K_(2)` is .A. `2:pi`B. `1:2`C. `pi:2`D. `3:2` |
|
Answer» Correct Answer - C `((Q)/(t))_("semicircularrod")=((Q)/(t))_("straightrod")` `(K_(1)A(Deltatheta))/(pir)=(K_(2)A(Deltatheta))/(2r)` r =` radius of semi circle . |
|
| 77. |
At high temperature black body spectrum is .A. continuous absorptionB. line absorptionC. continuous emissionD. line emission |
| Answer» Correct Answer - C | |
| 78. |
Assertion : The radiation from the sun’s surface varies as the fourth power of its absolute temperature. Reason : The sun is not a black body.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertionC. If assertion is true reason is falseD. If the assertion and reason both are false. |
|
Answer» Correct Answer - C |
|
| 79. |
The spectrum from a black body radiation is aA. Line spectrumB. Band spectrumC. Continuous spectrumD. Line and band spectrum both |
|
Answer» Correct Answer - C |
|
| 80. |
The rate of radiation from a black body at `1^(@)C` is `E` The rate of radiation from this black body at `273^(@)C` is .A. `2E`B. `E//2`C. `16 E`D. `E//16` |
|
Answer» Correct Answer - C `P=sigmaAT^(4)rArr(P_(1))/(P_(2))=((T_(1))/(T_(2)))^(4)("giventhat" P_(1)=E)` |
|
| 81. |
Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are same. The two bodies emit total radiant power at the same rate. The wavelength `lambda_B` corresponding to maximum spectral radiancy from B is shifted from the wavelength corresponding to maximum spectral radiancy in the radiation from A by 1.0 `mum`. If the temperature of A is 5802 K, calculate (a) the temperature of B, (b) wavelength `lambda_B`.A. the temperature of `B` is `1934K`B. `lambda_(B) = 1.5 mum`C. the temperature of `B` is `11604K`D. the temperature of `B` is 2901 K |
|
Answer» Correct Answer - A::B `e_(A) sigma T_(A)^(4) = e_(B) sigma T_(B)^(4), (T_(A))/(T_(B)) = ((e_(B))/(e_(A)))^(1/(4))=3` `T_(B) = (T_(A))/(3) =1934k lambda_(A)T_(A)=lambda_(B)T_(B)` `lambda_(A)=(lambda_(B))/(3),lambda_(B)-lambda_(A)=1mum,lambda_(B)=1.5m` . |
|
| 82. |
Two spherical bodies have radii `R,2R` and emissivities e,2e If the temperature ratio is `2:1` then the powers will be in the ratio .A. `1 :1`B. `2:1`C. `3:1`D. `4:1` |
|
Answer» Correct Answer - B `P = e sigma AT^(4) rArr P = e sigma 4 pi R^(20 T^(4)` `:.(P_(1))/(P_(2))((T_(1))/(T_(2)))(e_(1))/(e_(2))xx(R_(1))/(R_(2))` . |
|
| 83. |
Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are same. The two bodies emit total radiant power at the same rate. The wavelength `lambda_B` corresponding to maximum spectral radiancy from B is shifted from the wavelength corresponding to maximum spectral radiancy in the radiation from A by 1.0 `mum`. If the temperature of A is 5802 K, calculate (a) the temperature of B, (b) wavelength `lambda_B`.A. The temperature of B is 1934 KB. `lambda_(B) = 1.5 mu m`C. The temperature of B is 11604 KD. The temperature of B is 2901 K |
|
Answer» Correct Answer - A::B |
|
| 84. |
Two electric bulbs have filaments of lengths `L` and `2L` diameters `2d` and d and emissivities `3e` and 4e If their temperatures are in the ratio 2:3 their powers will be in the ratio of .A. `8:27`B. `4:27`C. `8:3`D. `4:9` |
|
Answer» Correct Answer - B `P =e sigma(4piR^(2))T^(4)rArr` `(P_(1))/(P_(2))=(e_(1))/(e_(2))xx(r_(1))/(r_(2))xx(l_(1))/(l_(2))xx((T_(1))/(T_(2)))^(4)` . |
|
| 85. |
Suppose the sun expands so that its radius becomes `100` times its present radius and its surface temperature becomes half of its present value. The total energy emited by it then will increase by a factor of :A. 10B. 625C. 256D. 16 |
|
Answer» Correct Answer - B |
|
| 86. |
A particular star (assuming it as a black body) has a surface temperature of about `5 xx 10^(4)K` The wave length in nano-meters at which its radiation becomes maximum is `(b = 0.0029mk)` .A. 48B. 58C. 60D. 70 |
|
Answer» Correct Answer - B |
|
| 87. |
The maximum energy is the thermal radiation from a hot source occurs at a wavelength of `11 xx 10^(-5) cm`. According to Wien’s law, the temperature of this source (on Kelvin scale) will be `n` times the temperature of another source (on Kelvin scale) for which the wavelength at maximum energy is `5.5 xx 10^(-5) cm`. The value of `n` is:A. 2B. 4C. `(1)/(2)`D. 1 |
|
Answer» Correct Answer - C |
|
| 88. |
The maximum energy in thermal radiation from a source occurs at the wavelength 4000Å. The effective temperature of the source iA. 7000 KB. 80000 KC. `10^(4) K`D. `10^(6) K` |
|
Answer» Correct Answer - A |
|
| 89. |
Statement-1 : As temperature of a black body is raised, wavelenght corresponding to which energy emitted is maximum, reduces. Statement-2 : Higher temperature would mean higher energy and hence higher wavelength.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertionC. If assertion is true reason is falseD. If the assertion and reason both are false. |
|
Answer» Correct Answer - C |
|
| 90. |
When the temperature of a black body increases, it is observed that the wavelength corresponding to maximum energy changes from `0.26mum` to `0.13mum`. The ratio of the emissive powers of the body at the respective temperatures isA. `(16)/(1)`B. `(4)/(1)`C. `(1)/(4)`D. `(1)/(16)` |
|
Answer» Correct Answer - D `P=sigmaAT^(4)`and`lambda_(m)xxT=const` `(P_(1))/(P_(2))=((T_(1))/(T_(2)))^(4)=((lambda_(2))/(lambda_(1)))^(4)` . |
|
| 91. |
The layers of atmosphere are heated throughA. ConvectionB. ConductionC. RadiationD. (b) and (c) both |
|
Answer» Correct Answer - A |
|
| 92. |
The length of the two rods made up of the same metal and having the same area of cross-section are 0.6 m and 0.8 m respectively. The temperature between the ends of first rod is `90^(@)` C and `60^(@)` C and that for the other rod is 150 and `110^(@)` C. For which rod the rate of conduction will be greaterA. FirstB. SecondC. Same for bothD. None of the above |
|
Answer» Correct Answer - C |
|
| 93. |
The ratio of thermal conductivity of two rods of different material is `5 : 4`. The two rods of same area of cross-section and same thermal resistance will have the lengths in the ratioA. `4 : 5`B. `9 : 1`C. `1 : 9`D. `5 : 4` |
|
Answer» Correct Answer - D |
|
| 94. |
Two identical plates of different metals are joined to form a single plate whose thickness is double the thickness of each plate. If the coefficients of conductivity of each plate are 2 and 3 respectively, Then the conductivity of composite plate will be |
|
Answer» Correct Answer - 2.4 |
|
| 95. |
Two identical plates of different metals are joined to form a single plate whose thickness is double the thickness of each plate. If the coefficients of conductivity of each plate are 2 and 3 respectively, Then the conductivity of composite plate will beA. 5B. 2.4C. 1.5D. 1.2 |
|
Answer» Correct Answer - B |
|
| 96. |
Assertion : A hollow metallic closed container maintained at a uniform temperature cab act as a source of black body radiation. Reason : All metals act as a black body.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertionC. If assertion is true reason is falseD. If the assertion and reason both are false. |
|
Answer» Correct Answer - C |
|
| 97. |
Which of the following statement is correctA. A good absorber is a bad emitterB. Every body absorbs and emits radiations at every temperatureC. The energy of radiations emitted from a black body is same for all wavelengthsD. The law showing the relation of temperatures with the wavelength of maximum emission from an ideal black body is Plank’s law |
|
Answer» Correct Answer - D |
|
| 98. |
A square is made of four rods of same material one of the diagonal of a square is at temperature difference `100^@C`, then the temperature difference of second diagonal:A. `0^(@)C`B. `(100)/(1).^(@)C`, where / is the length of each rodC. `(100)/(2l).^(@)C`D. `100^(@)C` |
|
Answer» Correct Answer - a |
|
| 99. |
One end of a copper rod of length 1.0 m and area of cross-section `10^(-3)` is immersed in boiling water and the other end in ice. If the coefficient of thermal conductivity of copper is `92 cal//m-s-.^(@)C` and the latent heat of ice is `8xx 10^(4) cal//kg`, then the amount of ice which will melt in one minute isA. `9.2 xx 10^(-3)kg`B. `8 xx 10^(-3) kg`C. `6.9 xx 10^(-3) kg`D. `5.4 xx 10^(-3) kg` |
|
Answer» Correct Answer - C |
|
| 100. |
The absorptivity of Lamp black and platinum black is .A. `0.91`B. `0.98`C. `1.00`D. `0.99` |
| Answer» Correct Answer - B | |