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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.
| 101. |
Two sheres made of same material have their radii in the ratio `1:3` They are heated to the same temperature and kept in the same surroudings at a moderate temperature Show that the ratio of their initial rates of fall of temperature is `3:1` if the bodies are cooled by natural convection and radiation . |
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Answer» The rate of fall to temperature of a hot body is given by `(d theta)/(dt) = (eAsigma)/(ms) (T^(4) -T_(0)^(4))` `:.(d"theta)/(dt) = (e4 pi R^(2) sigma(T^(4)-T_(0)^(2)))/((4)/(3) pi R^(3) rhos)rArr(d theta)/(dt) prop(1)/(R )` `((d theta//dt)_1)/((d theta//dt)_(2)) = (R_(2))/(R_(1)) = (3)/(1) ( :.(R_(1))/(R_(2) )=1:3)` Their ratio of fall of temperature is `3:1` . |
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| 102. |
One end of a copper rod of uniform cross section and length 1.5 m is kept in contact with ice and the other end with water at `100^@C`. At what point along its length should a temperature of `200^@C` be maintained so that in the steady state, the mass of ice melting be equal to that of the steam produced in same interval of time. Assume that the whole system is insulated from surroundings: `[L_("ice")=80 cal//g,L_("steam")=540 cal//g]`A. `8.59cm` from ice endB. `10.34` cm from water endC. `10.34` cm from ice endD. `8.76` cm from water end |
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Answer» Correct Answer - B `m_(ice)=(KA(200-0)t)/(80(1.5-x)),` `m_(steam)=(KA(200-100)t)/(540xxx)` According to given problem `m_(ice)=m_(steam)` . |
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| 103. |
If we place our hand below a lighted electric bulb We feel warmer because of .A. convectionB. radiationC. conductionD. both 1 and 2 |
| Answer» Correct Answer - B | |
| 104. |
On heating one end of a rod the temperature of the whole rod will be uniform when .A. `k =1`B. `k =0`C. `k =100`D. `k =oo` |
| Answer» Correct Answer - D | |
| 105. |
For an ideal conductor thermal resistance is .A. unityB. infinityC. zeroD. 1000 |
| Answer» Correct Answer - C | |
| 106. |
The physical factor distinguishes thermal radiation from visible light is .A. wavelenghtB. pressureC. temperatureD. amplitude |
| Answer» Correct Answer - A | |
| 107. |
For a small temperature difference between the body and the surroundings the relation between the rate of loss heat R and the temperature of the body is depicted byA. B. C. D. |
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Answer» Correct Answer - C |
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| 108. |
According to the experiment of Ingen Hausz the relation between the thermal conductivity of a metal rod is K and the length of the rod whenever the wax melts isA. K/l = constantB. `K^(2)//l`= constantC. `K//l^(2)`= constantD. Kl = constant |
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Answer» Correct Answer - C |
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| 109. |
If the ratio of coefficient of thermal conductivity of silver and copper is `10 : 9`, then the ratio of the length upto which wax will melt in Ingen Hauze experiment will beA. `6 : 10`B. `sqrt(10) : 3`C. `100 : 81`D. `81 : 100` |
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Answer» Correct Answer - B |
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| 110. |
Two identical metal balls at temperature `200^(@)C` and `400^(@)C` kept in air at `27^(@)C`. The ratio of net heat loss by these bodies isA. `1//4`B. `1//2`C. `1//16`D. `(473^(4)-300^(4))/(673^(4)-300^(4))` |
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Answer» Correct Answer - D |
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| 111. |
Heat travels through vaccum byA. ConductionB. ConvectionC. RadiationD. Both (a) and (b) |
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Answer» Correct Answer - C |
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| 112. |
If at temperature `T_(1) = 1000 K` the wavelength is `1.4 xx 10^(-6)m` then at what temperature the wavelength will be m `2.8 xx 10^(-6)m`A. 2000 KB. 500 KC. 250 KD. None of these |
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Answer» Correct Answer - A |
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| 113. |
The spectra of radiation emitted by two distant stars are shown below The ratio of the surface temperature of star `A` to that of star `B, T_(A) :T_(B)` is approximately .A. `2 :1`B. `4 :1`C. `1 :2`D. `1 :1` |
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Answer» Correct Answer - A `lambda_(MA)T_(A)=lambda_(MB)T_(B)("Weins law"),(T_(A))/(T_(B))=(lambda_(MB))/(lambda_(MA))=(1000)/(500)=2:1` . |
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| 114. |
The wavelength of maximum intensity of radiation emitted by a star is 289.8 nm . The radiation intensity for the star is : (Stefan’s constant `5.67 xx 10^(-8)Wm^(-2)K^(-4)`, constant `b = 2898 mu m K`)-A. `5.67 xx 10^(8) W//m^(2)`B. `5.67 xx 10^(12) W//m^(2)`C. `10.67 xx 10^(7) W//m^(2)`D. `10.67xx 10^(14) W//m^(2)` |
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Answer» Correct Answer - A |
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| 115. |
If a liquid is heated in weightlessness, the heat is transmitted throughA. ConductionB. ConvectionC. RadiationD. Neither, because the liquid cannot be heated in weightlessness |
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Answer» Correct Answer - A |
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| 116. |
Which of the following statements is wrong ?A. Rough surfaces are better radiators than smooth surfaceB. Highly polished mirror like surfaces are very good radiatorsC. Black surfaces are better absorbers than white onesD. Black surfaces are better radiators than white |
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Answer» Correct Answer - B |
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| 117. |
Two spheres made of same material have radii in the ratio 1: 2 Both are at same temperature. Ratio of heat radiation energy emitted per second by them isA. `1 : 2`B. `1 : 8`C. `1 : 4`D. `1 : 16` |
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Answer» Correct Answer - C |
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| 118. |
The original temperature of a black body is . `727^(@) C` . The temperature at which this black body must be raised so as to double the total radiant energy, isA. 971 KB. 1190 KC. 2001 KD. 1458 K |
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Answer» Correct Answer - B |
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| 119. |
Two identical rods of same metal are first waleded in series and then in parallel are maintained at same temperature difference then the ratio of heats conducted in same time is .A. `1 :1`B. `1:2`C. `1:4`D. `1:3` |
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Answer» Correct Answer - C `Q=(KA(Delta theta)t)/(l)` `(Q_(1))/(Q_(2))=(K_(s)A(Delta theta)t)/(2l)xx(l)/(K_(p)2A(DeltaA)t)("here "K_(s)=K_(p))` |
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| 120. |
Two rectangular blocks A and B of different metals have same length and same area of cross-section. They are kept in such a way that their cross-sectional area touch each other. The temperature at one end of A is `100^(@)C` and B at the other end is `0^(@)C`. If the ratio of their thermal conductivity is `1 : 3`, then under steady state, the temperature of the junction in contact will beA. `25^(@)C`B. `50^(@)C`C. `75^(@)C`D. `100^(@)C` |
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Answer» Correct Answer - A |
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| 121. |
The temperature drop through a two layer furnace wall is `900^@C`. Each layer is of equal area of cross section. Which of the following actions will result in lowering the temperature `theta` of the interface?A. By increasing the thermal conductivity of outer layer .B. By increasing the thermal conductivity of outer layer .C. By increasing the thermal conductivity of outer layer .D. By increasing the thermal conductivity of outer layer . |
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Answer» Correct Answer - A::B H =rate of heat flow `=(900)/((l_(1))/((K_(i)A))+(l_(0))/(K_(0A)))` Now, `1000 -theta = (Hl_(i))/(K_(i)A)or` `theta=1000-[(900)/((l_(i))/(K_(i0A))+(l_(0))/(K_(0)A))](l_(i))/(K_(i)A)=100-(900)/(1+(l_(0)K)/(K_(0))(K_(i))/(l_(i)))` Now we can see that `theta` can be decreased by increasing thermal conductivity of outer layer `(K_(0))` and thickness of inner layer `(I_(i))` . |
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| 122. |
On heating one end of a rod the temperature of the whole rod will be uniform when .A. K = 1B. K = 0C. K = 100D. ` K = oo` |
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Answer» Correct Answer - D |
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| 123. |
A calorimeter of mass `0.2 kg` and specific heat `900 J//kg-K`. Containing `0.5 kg` of a liquid of specific heat `2400 J//kg-K`. Its temperature falls from `60^(@)C` to `55^(@)C` in one minute. Find the rate of cooling.A. 5 J/sB. 15 J/sC. 100 J/sD. 115 J/s |
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Answer» Correct Answer - D |
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| 124. |
A body is kept inside a container the temperature of the body is `T_(1)` and the temperature of the container is `T_(2)` the rate at which body absorbs the energy is `alpha` The emissivity of the body is The radiation striking the body is either absorbed or reflected At what rate of body will basorb the radiant energy .A. `alpha`, but `alpha ne e`B. `(T_(1)-T_(2))//t` where is the timeC. e, but `e = alpha`D. None of these |
| Answer» Correct Answer - C | |
| 125. |
A body is kept inside a container the temperature of the body is `T_(1)` and the temperature of the container is `T_(2)` the rate at which body absorbs the energy is `alpha` The emissivity of the body is The radiation striking the body is either absorbed or reflected At what rate of body will absorb the radiant energy .A. If is the time,rate is `(T_(1)-T_(2))t`B. `e`C. both of the aboveD. None of these |
| Answer» Correct Answer - B | |
| 126. |
On increasing the temperature of a substance gradually, which of the following colours will be noticed by youA. WhiteB. YellowC. GreenD. Red |
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Answer» Correct Answer - A |
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| 127. |
A body takes 5 minutes for cooling from `50^(@)C ` to `40^(@)C` Its temperature comes down to `33.33^(@)C` in next 5 minutes. Temperature of surroundings isA. `15^(@)C`B. `20^(@)C`C. `25^(@)C`D. `10^(@)C` |
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Answer» Correct Answer - B |
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| 128. |
How is the temperature of stars determined byA. Stefan’s lawB. Wein’s displacement lawC. Kirchhoff’s lawD. Ohm’s law |
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Answer» Correct Answer - B |
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| 129. |
On investigation of light from three different stars A , B and C , it was found that in the spectrum of A the intensity of red colour is maximum, in B the intensity of blue colour is maximum and in C the intensity of yellow colour is maximum. From these observations it can be concluded thatA. The temperature of A is maximum, B is minimum and C is intermediateB. The temperature of A is maximum, C is minimum and B is intermediateC. The temperature of B is maximum, A is minimum and C is intermediateD. The temperature of C is maximum, B is minimum and A is intermediate |
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Answer» Correct Answer - C |
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| 130. |
Which of the prism is used to see infra-red spectrum of lightA. Rock-saltB. NicolC. FlintD. Crown |
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Answer» Correct Answer - A |
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| 131. |
A body is kept inside a container the temperature of the body is `T_(1)` and the temperature of the container is `T_(2)` the rate at which body absorbs the energy is `alpha` The emissivity of the body is The radiation striking the body is either absorbed or reflected Ater a long time the temperature of the body will be .A. `T_(1)`B. `T_(2)`C. `T_(1)+((T_(2)-T_(1)))/(2)`D. None the these |
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Answer» Correct Answer - (b) |
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| 132. |
A body is kept inside a container the temperature of the body is `T_(1)` and the temperature of the container is `T_(2)` the rate at which body absorbs the energy is `alpha` The emissivity of the body is The radiation striking the body is either absorbed or reflected At what rate of body will absorb the radiant energy .A. if t is the time , rate is `(T_(1)-T_(2))//t`B. eC. Both of the aboveD. None the above |
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Answer» Correct Answer - (b) |
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| 133. |
In an atomic bomb, the temperature of 10million degrees is developed at the moment of explosion In what region of the spectrum of explosion In what region of the spectrum do the wavelength corresponding to maximum energy density lie ? `( b =0.28 xx 10^(-2) S.I unit)` .A. Ultra-violetB. VisibleC. Infra-red raysD. x-rays |
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Answer» Correct Answer - D `lambda_(m)T=b` |
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| 134. |
Solar radiation emitted by sun resembles that emitted by a body at a temperature of `6000 K` Maximum intensity is emitted at a wavelength of about `4800A^(@)` If the sun was cooled down from `6000K` to `3000K` then the peak intensity would occure at a wavelenght of .A. `4800 Å`B. `9600Å`C. `7200Å`D. `6400Å` |
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Answer» Correct Answer - B |
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| 135. |
Solar radiation emitted by sun resembles that emitted by a body at a temperature of `6000 K` Maximum intensity is emitted at a wavelength of about `4800A^(@)` If the sun was cooled down from `6000K` to `3000K` then the peak intensity would occure at a wavelenght of .A. `4800 A^(@)`B. `9600 A^(@)`C. `2400 A^(@)`D. `19200 A^(@)` |
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Answer» Correct Answer - B `lambda_(m)xxT =` constant, `lambda_(1)T_(1)=lambda_(2)T_(2)` |
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| 136. |
Mode of transmission of heat, in which heat is carried by the moving particles, isA. RadiationB. ConductionC. ConvectionD. Wave motion |
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Answer» Correct Answer - C |
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| 137. |
In a closed room, heat transfer takes place byA. ConductionB. ConvectionC. RadiationD. All of these |
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Answer» Correct Answer - B |
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| 138. |
If the end of metal rod is heated then the rate of flow the heat does not depend onA. area of end of the rodB. mass of the rodC. timeD. temperature gradient |
| Answer» Correct Answer - B | |
| 139. |
Which of the following methods of flow of heat is (are) based on gravitational attraction ?.A. Natural convectionB. ConductionC. RadiationD. Stirring of liquids |
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Answer» Correct Answer - A |
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| 140. |
Energy is being emitted from the surface of a black body at `127^(@)C` temperature at the rate of `1.0xx10^(6)J//sec-m^(2)`. Temperature of the black at which the rate of energy emission is `16.0xx10^(6)J//sec-m^(2)` will be |
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Answer» Correct Answer - `527^(@)C` |
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| 141. |
Energy is being emitted from the surface of a black body at `127^(@)C` temperature at the rate of `1.0xx10^(6)J//sec-m^(2)`. Temperature of the black at which the rate of energy emission is `16.0xx10^(6)J//sec-m^(2)` will beA. `254^(@)C`B. `508^(@)C`C. `527^(@)C`D. `727^(@)C` |
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Answer» Correct Answer - C |
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| 142. |
A rod of unifrom cross section is heated at temperature `t_(0)` at a point which is at `n_(1)` times if its length `(n_(1) lt 1)` from its one end in stready state The temperature at this end is `t_(1)` and at other end is `t_(2)` Rate of vapourisation of water at either end of the rod is same. The end at which temperature is `t_(2)` is how much more far away that the other end from the point at which the rod is heated .A. `(n_(1)(t_(0)-t_(2)))/(t_(0)-t_(1))`B. `(n_(1)(t_(0)-t_(2)))/(t_(0)-t_(1))`C. `(2n_(1)t_(0))/(t_(0)-t_(2))`D. `(2n_(1)(t_(1)-t_(2)))/(t_(0)-t_(1))` |
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Answer» Correct Answer - D `(dQ)/(dt)=L(dm)/(dt),(dm)/(dt)=(KA)/(l).(DeltaT)/(L),((dm)/(dt))_(1)=((dm)/(dt))_(2)` `(t_(0)-t_(1))/(n_(1)lL)=(t_(0)-t_(2))/(n_(2)lL),(n_(2))/(n_(1))= (t_(0)-t_(2))/(t_(0)-t_(1))` `(n_(2)-t_(1))/(n_(1))=(Deltan)/(n_(1))=(t_(1)-t_(2))/(t_(0)-t_(1))` `(n_(2)-n_(1))/(n_(1))=(Deltan)/(n_(1))=(t_(1)-t_(2))/(t_(0)-t_(1))` . |
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| 143. |
A black body does not .A. emit radiationB. reflect radiationC. absorb radiationD. emit and absorb radiation |
| Answer» Correct Answer - B | |
| 144. |
The best laboratory approximation to an ideal black body is .A. lump of charocoal heated to high temperatureB. a glass surface coated with coal tarC. a metal coated with black dyeD. a hollow enclosure blackened inside with lamp black and have a small hole |
| Answer» Correct Answer - D | |
| 145. |
Relation between the colour and the temperature of a star is given byA. Wein’s displacement lawB. Planck’s lawC. Hubble’s lawD. Fraunhofer diffraction law |
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Answer» Correct Answer - A |
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| 146. |
The colour of a star is a measure of its .A. ageB. temperatureC. sizeD. distance from the earth |
| Answer» Correct Answer - B | |
| 147. |
The wavelength of radiation emitted by a body depends uponA. The nature of its surfaceB. The area of its surfaceC. The temperature of its surfaceD. All the above factors |
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Answer» Correct Answer - C |
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| 148. |
Which of the following law states that "good absorbers of heat are good emitters"A. Stefan’s lawB. Kirchoff’s lawC. Planck’s lawD. Wein’s law |
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Answer» Correct Answer - B |
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| 149. |
Air is bad conductor of heat or partly conducts heat, still vacuum is to be placed between the walls of the thermos flask becauseA. It is difficult to fill the air between the walls of thermos flaskB. Due to more pressure of air, the thermos can get crackC. By convection, heat can flow through airD. On filling the air, there is no advantage |
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Answer» Correct Answer - C |
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| 150. |
For cooking the food, which of the following type of utensil is most suitableA. High specific heat and low conductivityB. High specific heat and high conductivityC. Low specific heat and low conductivityD. Low specific heat and high conductivity |
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Answer» Correct Answer - D |
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