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.
| 1. |
Liquid is filled in a vessel which is kept in a room with temperature 20°C. When the temperature of the liquid is 80°C, then it loses heat at the rate of 60 cal/sec. What will be the rate of loss of heat when the temperature of the liquid is 40°C ?A. `180 cal//sec`B. `40 cal // sec`C. `30 cal // sec`D. `20 cal //sec` |
|
Answer» Correct Answer - D |
|
| 2. |
The temperature at which a black body of unit area loses its energy at the rate of 1 joule/second isA. `-65^(@)C`B. `65^(@)C`C. 65 KD. None of these |
|
Answer» Correct Answer - C |
|
| 3. |
Assertion : The equivalent thermal conductivity of two plates of same thickness in contact (series) is less than the smaller value of thermal conductivity. Reason : For two plates of equal thickness in contact (series) the equivalent thermal conductivity is given by `1/K = 1/K_(1) + 1/K_(2)`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 - D |
|
| 4. |
An incandesent light bulb has a tungsten filament that is heated to a temperature `3 xx 106(3)K` when an electric current passes through it If the surface area of the filament is approximately `10^(-4)m m^(2)` and it has an emissivity of `0.3` the power radiated by the bulb is nearly `(sigam = 5.67 xx 10^(-8) W m^(-2) K^(-4))` .A. `138 w`B. `175 w`C. `200 w`D. `225 w` |
|
Answer» Correct Answer - A `P=eAsigmaT^(4)` |
|
| 5. |
An incandesent bulb has a thin filament of tungsten that is heated to high temperature by passing an electric current The hot filament emits black-body radiation The filament is observed to break up at random locations after a sufficiently long time of operation due to non-uniform evapo ration of operation due to non-uniform evapo ration of ungsten from the filament If the buld is powered at constant voltage which of the following statement (s) is (are) ture ? .A. The temperature distribution over the filament is uniformB. The resistance over small sections of the filament decreases with timeC. The filament emits more light at higher band of frequencies before it breaks upD. The filament consumes less electrical power to words the end of the life of the bulb |
|
Answer» Correct Answer - C::D Towards the end of the life filament will become thinner. Resistance will increase and so consumed power will be less, so it will emit less light Temperature distribution will be non uniform At the position where temperature is maximum filament will break. Black body radiation curve will become flat so the filament consumes less electrical power towards the end of the life of the bulb . |
|
| 6. |
The temperature across two different slabs A and B are shown I the steady state (as shown Fig) The ratio of thermal conductivities of A and B isA. `2:3`B. `3:2`C. `1:1`D. `5:3` |
|
Answer» Correct Answer - B `((dQ)/(dt))xx(1)/(A)=K_(A)((50-30))/(3)=K_(B)((50-20))/(3)` `2KA = 3KB or KA//KB =3//2` . |
|
| 7. |
Three metal rods of same lenghs and same area of cross sections having conductivities `1,2,3,` units are connected in series Then their effective conductivity will be .A. 2 unitsB. `1.6` unitsC. `2.4` unitsD. `2.8` units |
|
Answer» Correct Answer - B `R_(eff) =R_(1) +R_(2) +R_(3)` `(l_(1)+l_(2)+l_(3))/(K_(eff))=(l_(1))/(K_(1))+(l_(2))/(K_(2))+(l_(3))/(K_(3))` . |
|
| 8. |
A slab of stone area `3600 cm^(2)` and thickness `10cm` is exposed on the lower surface to steam at `100^(@)C` A block of ice at `0^(@)C` rest on upper surface of the slab. In one hour `4.8kg` of ice is melted. The thermal conductivity of the stone in `Js^(-1)m^(-1)k^(-1)` is (latent heat of ice `=3.36 xx 10^(5) J//Kg` .A. `12.0`B. `10.5`C. `1.02`D. `1.24` |
|
Answer» Correct Answer - D `(mL)/(t)=(KADeltatheta)/(X)` |
|
| 9. |
Two walls of thickness d and d and thermal conductivities k and k are in contact. In the steady state, if the temperature at the outer `T_(1)` and `T_(2)` , the temperature at the common wall isA. `(k_(1)T_(1)d_(2)+k_(2)T_(2)d_(1))/(k_(1)d_(2)+k_(2)d_(1))`B. `(k_(1)T_(1)+k_(2)d_(2))/(d_(1)+d_(2))`C. `((k_(1)d_(1)+k_(2)d_(2))/(T_(1)+T_(2)))T_(1)T_(2)`D. `(k_(1)d_(1)T_(1)+k_(2)d_(2)T_(2))/(k_(1)d_(1)+k_(2)d_(2))` |
|
Answer» Correct Answer - A |
|
| 10. |
A hollow sphere of glass whose external and internal radii are `11cm` and `9cm` respec-tively is completely filled with ice at `0^(@)C` and placed in a both of boiling water How long will it take for the ice to melt completely ? Givne that density of ice `=0.9g//cm^(3)` latent heat of fusion of ice `=80 cal//g` and thermal conductivity of glass `=0.002 cal//cm-s^(@)C` . |
|
Answer» In steady state, rate of heat flow `H =(4piKr_(1)r_(2)Deltatheta)/(r_(2)-r_(1))` Substituting the values `H=((4)(pi)(0.002)(11)(9)(100-0))/((11-9))` or `(dQ)/(dt) =124.4cal//s,(dQ)/(dt) = L (dm)/(dt)` ltbr gt `:.((dm)/(dt)) =(dQ//dt)/(L) = (124.4)/(80) =1.555g//s` Total mass of ice `m =rho_(ice) (4pi r_(1)^(2)) = (0.9) (4) pi(9)^(2)` `:.` Time taken for the ice to melt completely `t = (m)/((dm//dt)) = (916)/(1.555) =589s` . |
|
| 11. |
A cube of side `10cm` is filled with ice of density `0.9//c.c` Thickness of the walls of the cube is `1mm` and thermal conductivity of the material of the cube is steam bath maintained at a placed in steam bath maintained at a temperature of `100^(@)C` the time in which ice completely melts is `(L_(ice)=80cal//gm)` .A. `6 sec`B. `12 sec`C. `24 sec`D. `48 sec` |
|
Answer» Correct Answer - B `mL_(ice)=(KA(Deltatheta)t)/(d)` `rho_(ice)(a)^(3)L_(ice)=(K(6a^(2))(Deltatheta)t)/(d)` here, a d are side and thickness of cube Heat conducts through six faces . |
|
| 12. |
Two hollow supheres of thickness are filled with ice The ratio of their diameter is `1:2` and the materials is `2 :3` The ratio of times in which the ice gets melted in the two spheres is .A. `3 :4`B. `4 :3`C. `3 :8`D. `8 :3` |
|
Answer» Correct Answer - A `mL_(ice)=(KA(Deltatheta)t)/(d)rArr(4)/(3)piR^(3)rhoccxxL_(ice)=(K4piR^(2)(Deltatheta)t)/(d)` `:.(t_(1))/(t_(2))=(R_(1))/(R_(2))xx(K_(2))/(K_(1))` |
|
| 13. |
Two hollow suphers of same material one with double the radius of the other and double the thickness of the other filled with ice, the ratio of time in which ice gets melted in the two spheres is .A. `2:1`B. `1:2`C. `4:1`D. `1:4` |
|
Answer» Correct Answer - C `mL_(ice)=(KA(Deltatheta)t)/(d)rArr(4)/(3)piR^(3)rhoxxL_(ice)=(K4piR^(2)(Deltatheta)t)/(d)` `:.(t_(1))/(t_(2))=((R_(1))/(R_(2)))+(d_(1)/(d_(2)))` . |
|
| 14. |
A wall has two layers A and B each made of different materials. Both the layers have the same thickness. The thermal conductivity of materials A is twice of B. Under thermal equilibrium temperature difference across the layer B is `36^@C`. The temperature difference across layer A isA. `6^(@)`CB. `12^(@)`CC. `18^(@)`CD. `24^(@)`C |
|
Answer» Correct Answer - B |
|
| 15. |
A wall has two layers A and B each made of different materials. Both the layers have the same thickness. The thermal conductivity of materials A is twice of B. Under thermal equilibrium temperature difference across the layer B is `36^@C`. The temperature difference across layer A isA. `6^(@)C`B. `12^(@)C`C. `18^(@)C`D. `24^(@)C` |
|
Answer» Correct Answer - B |
|
| 16. |
Three rods `A,B` and `C` have the same dimensions Their conductivities are `K_(A)` K and `K_(C)` respectively `A` and `B` are placed end to end with their free ends kept at certain temperature difference `C` is placed separately with its ends kept at same temperature difference The two arrangements conduct heat at the same rate `K_(c)` must be equal to .A. `K_(A)+K_(B)`B. `(K_(A)+K_(B))/(K_(A)K_(B))`C. `(1)/(2)(K_(A)+K_(B))`D. `(K_(A)+K_(B))/(K_(A)K_(B))` |
|
Answer» Correct Answer - D When `A` and `B` are in series `(l_(1)+l_(2))/(K_(eff))=(l_(1))/(K_(1))+(l_(2))/(K_(2))rArrK_(eff)=(2K_(A)K_(B))/(K_(A)+K_(B))` `(Q)/(t)=((2K_(A)K_(B))/(K_(A)+K_(B)))A(Deltatheta)....(i)` For rod `C (Q)/(t) = (K_(C)A(Deltatheta))/(t)...(ii)` From (i) and (ii) we get value of `K_(C)` . |
|
| 17. |
Three different arrangemnets of matrials `1` and `2,3` to from a wall Thremal conductivities are `k_(1) gt k_(2) gt k_(3)` The left side of the wall is `20^(@)C` higher than the right side Temperature difference `DeltaT` across the material 1 has following relation in three cases A. `DeltaT_(a) gt Deltab+_(b) gtdeltaT_(c)`B. `DeltaT_(c) = DeltaT_(b) =DeltaT_(c)`C. `DeltaT_(a) =DeltaT_(b) gt DeltaT_(c)`D. `DeltaT_(a) =DeltaT_(b) lt DeltaT_(c)` |
|
Answer» Correct Answer - B since the rate of heat flow will be same in all the three cases so the temperature diffrence will also be same across wall 1 because it has same parameteres in all the cases . |
|
| 18. |
A slab consists of two layers of different materials of the same thickness and having thermal conductivities `K_(1)` and `K_(2)`. The equivalent thermal conductivity of the slab isA. `K_(1)+K_(2)`B. `(K_(1)+K_(2))/(2)`C. `(2K_(1)K_(2))/(K_(1)+K_(2))`D. `(K_(1)+K_(2))/(2K_(1)K_(2))` |
|
Answer» Correct Answer - B |
|
| 19. |
Two rods of different materials having differnet lengths and same cross sectional areas are joined end to end in a straight line. The free ends of this compound rod are maintained at different temperatures The temperature gradient in each rod will be .A. sameB. zeroC. directly proportional to thermal conductivity of rodD. inversely proportional to thermal conductivity of the rod . |
| Answer» Correct Answer - D | |
| 20. |
Five rods of same dimensions are arranged as shown in the figure. They have thermal conductivities `K _(1) , K_(2) , K _(3) , K_( 4)` and `K_( 5)` . When points A and B are maintained at different temperatures, no heat flows through the central rod if A. `K_(1)=K_(4)` and `K_(2)=K_(3)`B. `K_(1)K_(4) = K_(2)K_(3)`C. `K_(1)K_(2) = K_(3)K_(4)`D. `(K_(1))/(K_(4))=(K_(2))/(K_(3))` |
|
Answer» Correct Answer - B |
|
| 21. |
Three rods `AB,BC`and `BD` having thremal conductivities in the ratio `1:2:3` and lengths in the ratio `2:1:1` are joined as shown in The ends `A,C` and `D` are at temperature `theta_(1),theta_(2)` and `theta_(3)` respectively Find the temperature of the junction `B` (Assume steady state and `theta_(1)gt theta gt theta_(2)gttheta_(3))` . |
|
Answer» Let the thermal conductivities of the rods `AB,BC` and `BD` be `K,2K` and `3K` respectively and their lenths be `2L,L` and `L` we have `[(DeltaQ)/(Deltat)]_(AB)=[(DeltaQ)/(Deltat)]_(BC)+[(DeltaQ)/(Deltat)]_(BD)` `i.e(KA(theta_(1)-theta))/(2L) =(2KA(theta-theta_(2)))/(L)+(3KA(theta-theta_(3)))/(L)` `:.theta=(1)/(11) (theta_(1)+4theta_(2)+6theta_(3))` . |
|
| 22. |
Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Each rod is of the same length. The left and right ends are kept at `0^@C` and `90^@C`, respectively. The temperature of junction of the three rods will be (a) `45^@C` (b) `60^@C` (c) `30^@C` (d) ` 20^@C`. A. `45^(@)C`B. `60^(@)C`C. `30^(@)C`D. `20^(@)C` |
|
Answer» Correct Answer - B |
|
| 23. |
Two rods of same length and cross section are joined along the length. Thermal conductivities of first and second rod are `K_(1)` and `K_(2)`. The temperature of the free ends of the first and seconds rods are maintained at `theta_(1)` and `theta_(2)` respectively. The temperature of the common junction isA. `(theta_(1)+theta_(2))/(2)`B. `(K_(2)K_(2))/(K_(1)+K_(2))(theta_(1)+theta_(2))`C. `(K_(1)theta_(1)+K_(2)theta_(2))/(K_(1)+K_(2))`D. `(K_(2)theta_(1)+K_(1)theta_(2))/(K_(1)+K_(2))` |
|
Answer» Correct Answer - C |
|
| 24. |
The end of two rods of different materials with their thermal conductivities, area of cross-section and lengths all in the ratio 1:2 are maintained at the same temperature difference. If the rate of flow of heat in the first rod is `4 cal//s`. Then, in the second rod rate of heat flow in `cal//s ` will beA. 1B. 2C. 8D. 16 |
|
Answer» Correct Answer - A |
|
| 25. |
The coefficient of thermal conductivity of copper is nine times that of steel. In the composite cylindrical bar shown in Fig. what will be the temperature at the junction of copper and steel ?A. `75^(@)C`B. `67^(@)C`C. `33^(@)C`D. `25^(@)C` |
|
Answer» Correct Answer - A |
|
| 26. |
The templitude of radiations from a cylindrical heat source is related to the distance is .A. `A prop 1//d^(2)`B. `A prop(1)/sqrtd`C. `A prop d`D. `A prop d^(2)` |
| Answer» Correct Answer - B | |
| 27. |
Two rods `A` and `B` of same metal and of same cross-section have length in the ratio `1:2` One end of each rod is at `O^(@)C` and temperature of other ends are `30^(@)C` and `40^(@)C` respectively Which of the rod will have higher flow of heat ? .A. Rod AB. Rod BC. Both will have sameD. Depends upon the shape |
| Answer» Correct Answer - A | |
| 28. |
While measuring the thermal conductivity of liquids the upper part is kept hot and lower cooled so that .A. Convection may be stoppedB. Radiation may be stoppedC. Heat conduction is easier downwardsD. It is easier and more convenient to do so |
|
Answer» Correct Answer - A |
|
| 29. |
For a perfect insulator coefficient of thermal conductivity is .A. zeroB. infinireC. oneD. two |
| Answer» Correct Answer - A | |
| 30. |
While measuring the thermal conductivity of liquids the upper part is kept hot and lower cooled so that .A. convectional flow is stoppedB. radiation is stoppedC. conduction is easierD. it is easire to perform the experiment |
| Answer» Correct Answer - A | |
| 31. |
Two circular disc `A` and `B` with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do your draw from their cooling curves? A. `A` and `B` have same specific heatsB. Specific heat of `A` is lessC. Specific heat of `B` is lessD. Nothing can be said |
| Answer» Correct Answer - B | |
| 32. |
One end of a cylindrical rod is kept in steam chamber and the other end in melting Ice. Now `0.5gm` of ice melts in `1sec` if the rod is replaced by another rod of same length half the diameter then rate of melting of ice will be (in gm/sec) .A. `0.25`B. `0.5`C. `1`D. `2` |
|
Answer» Correct Answer - A `mL_(f)=(KA(Deltatheta)t)/(l)` `rArr((m)/(t))_(2)/((m)/(t))_(1)=(K_(2))/(K_(1))((d_(2))/(d_(1)))^(2)=d=` dia meter |
|
| 33. |
Certain substance emits only the wavelengths `lamda_1,lamda_2,lamda_3` and `lamda_4` when it is at a high temperature, it will absorb only the following wavelengthsA. `lambda_(1)`B. `lambda_(2)`C. `lambda_(1)` and `lambda_(2)`D. `lambda_(1),lambda_(2),lambda_(3)` and `lambda_(4)` |
|
Answer» Correct Answer - D |
|
| 34. |
Compared to a person with white skin another person with dark skin will experience .A. Less heat and more coldB. More heat and more coldC. More heat and less coldD. Less heat and less cold |
|
Answer» Correct Answer - B |
|
| 35. |
A solid copper shere of density `rho` specific heat c and radius r is at temperature `T_(1)` It is suspended inside a chamber whose walls are at temperature 0 `K` The time required for the temperature of sphere to drop to `T_(2)` is `(rrhoc)/(xesigma)((1)/(T_(2)^(3))-(1)/(T_(1)^(3)))` Find the value of x? Take the emmissivity of teh sphere to be equal to e . |
|
Answer» Correct Answer - 9 The rate of loss of energy due to radiation `P = eA sigmaT^(4) …T` is rate must be equal to mc `(dT)/(dt)` Hence `-mc (dT)/(dt) eAsigmaT^(4)` Negative sign is used at temperature decreases with time In this equation `((4)/(3) pir^(3)) rho` and `A =4pir^(2)` `:. (dT)/(dt)=(3esigma)/(rhocr)T^(4)or,-underset(0)overset(t)intdt=(rrhoc)/(3esigma)underset(T_(1))overset(T_(2))int(dT)/(T^(4))` Solving this, we get `t=(rrhoc)/(9esigma)((1)/(T_(2)^(3))-(1)/(T_(1)^(3)))` . |
|
| 36. |
A black body of temperature `T` is inside a chamber of temperature `T_(0)` Now the closed chamber is slightly opened to Sun that temeperature of black body `(T)` and chamber `(T_(0))` remain constant .A. Black body will absorb more radiation from the Sun .B. Black body will absorb less radiation from the Sun .C. Black body emits more thermal energyD. Black body emits thermal energy equal to the thermal energy absorbed by it . |
| Answer» Correct Answer - D | |
| 37. |
The bodies have thermal capacities in the ratio `3:4` and the rates of loss of heat in the ratio `3:5` Their rates of cooling will be in the ratio of .A. `9 :20`B. `4:5`C. `5:4`D. `1:1` |
|
Answer» Correct Answer - B `(dQ)/(dt) =ms((d theta)/(dt))` |
|
| 38. |
Cooling graphs are drawn for three liquids a,b and c The specific heat is maximum for liquid .A. `a`B. `b`C. `c`D. for all the three a,b and c |
| Answer» Correct Answer - A | |
| 39. |
Three identical shperes of different meterials iron gold and silver are at the same temperature The one that radiates more energy is .A. GoldB. SilverC. IronD. All radiate equally |
| Answer» Correct Answer - D | |
| 40. |
When heat flows through a wire of uniform cross section under steady state, thenA. temperature gradient is same every whereB. temperature at a particular point remains sameC. rate of heat flow is same at all cross sectionsD. all the above |
| Answer» Correct Answer - D | |
| 41. |
The temperature of hot and cold end of a 20 cm long rod in thermal steady state are at `100^(@)C` and `20^(@)C` respectively. Temperature at the centre of the rod isA. `50^(@)C`B. `60^(@)C`C. `40^(@)C`D. `30^(@)C` |
|
Answer» Correct Answer - B |
|
| 42. |
meter rod of area of cross section `4mc^(2)` with `K =0.5 cal g^(-1) C^(-1)` is observed that at steady state `360` cal of heat flows per minute The temperature gradient along the rod is .A. `3^(@)C//cm`B. `6^(@)C//an`C. `12^(@)C//m`D. `20^(@)C//cm` |
|
Answer» Correct Answer - A `Q=(KA(theta_(1)-theta_(2))t)/(l)` |
|
| 43. |
In a steady state of thermal conduction, temperature of the ends A and B of a 20 cm long rod are `100^(@)C` and `0^(@)C` respectively. What will be the temperature of the rod at a point at a distance of 6 cm from the end A of the rodA. `-30^(@)C`B. `70^(@)C`C. `5^(@)C`D. None of the above |
|
Answer» Correct Answer - B |
|
| 44. |
In a steady state of heat conduction the temperature of the ends `A` and `B` of a rod `100cm` long per `0^(@)C` and `100^(@)C` The temperature of the rod at a point `60cm` distant from the end `A` is .A. `0^(@)C`B. `40^(@)C`C. `60^(@)C`D. `100^(@)C` |
|
Answer» Correct Answer - C `Q=(KA(Deltatheta)t)/(l)rArr(theta_(1)-theta_(2))/(L)=(theta-theta_(2))/(l)` |
|
| 45. |
The distance of the Earth from the Sun is 4 times that of the planet Mercury from the Sun The temperature of the Earth in radiative equilibrium with the Sun is `290K` The radiative euilibrium temperature of the Mercury is `5.80 xx 10^(n)` Find the value of n Assume all three bodies to be black body . |
|
Answer» Correct Answer - 2 `P_("recieved")=(piR_(p)^(2))((P_(sun))/(4pir_(s)^(2)))` `P_("emitted")=sigma(e)4piR_(p)^(2)T_(p)^(4)` In equilibrium `P_(r) = P_(e)` `rArr (T_(p))^(2) alpha (1)/(r_(s))` `T_(earth)/(T_(mercury))=sqrt(r_(mercury)/(r_(earth)))` . |
|
| 46. |
In the steady state the two ends of a meter rod are at `30^(@)C` and `20^(@)C` the temperature at the `40^(th) cm` from the end at higher temperature is .A. `22^(@)C`B. `26^(@)C`C. `25^(@)C`D. `24^(@)C` |
|
Answer» Correct Answer - B `Q=(KA(Deltathetat))/(l)rArr(theta_(1)-theta_(2))/(L)=(theta-theta_(1))/(t)` |
|
| 47. |
A system `S` receives heat continuously from an electric heater of power `10 W`. The temperature of `S` becomes constant at `50^(@)C` when the surrounding temperature is `20^(@)C`. After the heater is switched off, `S` cools from `35.1^(@)C` to `34.9^(@)C` in `1 minute`. the heat capacity of `S` isA. `750J(.^(@)C)^(-1)`B. `1500J(.^(@)C)^(-1)`C. `3000J(.^(@)C)^(-1)`D. `6000J(.^(@)C)^(-1)` |
|
Answer» Correct Answer - B `(dQ)/(dt) prop T -T_(0) , 10 = beta (50 -20), beta = (1)/(3)` `(ms)((theta_(1)-theta_(2)))/(t) =beta((theta_(1)+theta_(2))/(2)-theta_(s))` here `theta_(1) = 35. 1^(@) C, theta_(2) = 34.9^(@)C` . |
|
| 48. |
Following graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperatureA. B. C. D. |
|
Answer» Correct Answer - C |
|
| 49. |
Two thermometers A and B are exposed in sunlight. The bulb of A is painted black, But that of B is not painted. The correct statement regarding this case isA. Temperature of A will rise faster than B but the final temperature will be the same in bothB. Both A and B show equal rise in beginningC. Temperature of A will remain more than BD. Temperature of B will rise faster |
|
Answer» Correct Answer - A |
|
| 50. |
A cup of tea cools from `80^(@)C` to `60^(@)C` in one minute. The ambient temperature is `30^(@)C` . In cooling from `60^(@)C` to `50^(@)C` it will takeA. 30 secondsB. 60 secondsC. 90 secondsD. 50 seconds |
|
Answer» Correct Answer - D |
|