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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.
| 151. |
A point source of heat of power P is placed at the centre of a spherical shell of mean radius R. The material of the shell has thermal conductivity K. If the temperature difference between the outer and inner surface of the shell in not to exceed T, the thickness of the shell should not be less than .......A. `(4piKR^(2)T)/(P)`B. `(4piKR^(2))/(TP)`C. `(4piR^(2)T)/(KP)`D. `(4piR^(2)T)/(KT)` |
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Answer» Correct Answer - A Rate of heat flow `(Q)/(t) = P =(K(4piR^(2))Deltatheta)/(d)` d=Thickness of shell . |
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| 152. |
The radiant energy from the Sun incident normally at the surface of earth is `20kcal//m^(2)` min What would have been the radiant energy incident normally on the earth if the sun had a temperature twice of the present one ? .A. `40kcal//(m^(2)-min)`B. `80kcal//(m^(2)-min)`C. `160kCal//(m^(2)-min)`D. `320Kcal(m^(2)-min)` |
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Answer» Correct Answer - D `E=sigmaT^(4)rArr(E_(1))/(E_(2))=((T_(1))/(T_(2)))^(4)` |
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| 153. |
Mud houses are cooler in summer and warmer in winter becauseA. Mud is superconductor of heatB. Mud is good conductor of heatC. Mud is bad conductor of heatD. None of these |
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Answer» Correct Answer - C |
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| 154. |
When a body has the same temperature as that of its surroundingsA. it does not radiate heatB. it radiates same quantity of heat as it receives from the surroundingsC. it radiates same quantity of heat as it receives from the surroundingsD. it radiates same quantity of heat as it receives from the surroundings |
| Answer» Correct Answer - B | |
| 155. |
A body takes 5 minutes to cool from `90^(@)C` to `60^(@)C` . If the temperature of the surroundings is `20^(@)C` , the time taken by it to cool from `60^(@)C` to `30^(@)C` will be.A. 5 minB. 8 minC. 11 minD. 12 min |
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Answer» Correct Answer - C |
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| 156. |
A body initially at `80^(@)C` cools to `64^(@)C` in 5 minutes and to `52^(@)C` in 10 minutes. What is the temperature of the surroundings?A. `26^(@)C`B. `49^(@)C`C. `35^(@)C`D. `42^(@)C` |
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Answer» Correct Answer - B |
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| 157. |
In the Ingen Hauz’s experiment the wax melts up to lengths 10 and 25 cm on two identical rods of different materials. The ratio of thermal conductivities of the two materials isA. `1 : 6.25`B. `6.25 : 1`C. `1 : sqrt(2.5)`D. `1 : 25` |
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Answer» Correct Answer - A |
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| 158. |
Temperature of water at the surface of lake is `- 20^(@)C`. Then temperature of water just below the lower surface of ice layer isA. `-4^(@)C`B. `0^(@)C`C. `4^(@)C`D. `-20^(@)C` |
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Answer» Correct Answer - B |
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| 159. |
Two identical rods of copper and iron are coated with wax uniformly. When one end of each is kept at temperature of boiling water, the length upto which wax melts are 8.4 cm and 4.2 cm respectively. If thermal conductivity of copper is 0.92, then thermal conductivity of iron isA. 0.23B. 0.46C. 0.115D. 0.69 |
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Answer» Correct Answer - A |
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| 160. |
The thickness of ice in a lake is `5cm` and the atmospheric temperature is `10^(@)C` Calculate the time rquired for the thickness of ice to grow to `7cm` Therml conductivity for ice `=4 xx 10^(-3) cal cm^(-1) s^(-1) c^(-10` density of ice `=0.92 g //cm^(3)` and latent heat of fusion of ice `=80 cal//g` . |
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Answer» `Delta t=(rhoL)/(2KT)(x_(2)^(2))` `= (92xx10^(-2))/(2xx4xx10^(-3))xx(80)/(10^(@))(7^(2)-5^(2))` `= 22080 s=6.13 Hr` |
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| 161. |
The heat is flowing through a rod of length 50 cm and area of cross-section `5cm^(2)` . Its ends are respectively at `25^(@)C` and `125^(@)C` . The coefficient of thermal conductivity of the material of the rod is `0.092 kcal // m × s ×.^(@) C` . The temperature gradient in the rod isA. `2^(@)C//cm`B. `2^(@)C//m`C. `20^(@)C//m`D. `20^(@)C//cm` |
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Answer» Correct Answer - A |
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| 162. |
Heat is flowing through a conductor of length l from x = 0 to x = l . If its thermal resistance per unit length is uniform, which of the following graphs is correctA. B. C. D. |
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Answer» Correct Answer - C |
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| 163. |
Radius of a conductor increases uniformly from left end to right end as shown in fig. Material of the conductor is isotropic and its curved surface is thermally isolated from surrounding. Its ends are maintained at temperatures `T_(1)` and `T_(2) ( T_(1) gt T_(2))`: If, in steady state, heat flow rate is equal to H , then which of the following graphs is correctA. B. C. D. |
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Answer» Correct Answer - B |
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| 164. |
Assertion : Radiation is the speediest mode of heat transfer. Reason : Radiation can be transmitted in zig-zag motion.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. |
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Answer» Correct Answer - C |
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| 165. |
A black body radiates energy at the rate of `E "watt"//m^(2)` at a high temperature `TK` when the temperature is reduced to `[(T)/(2)]K` Then radiant energy is . |
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Answer» Correct Answer - D `E=sigmaT^(4)rArr(E_(1))/(E_(2))=((T_(1))/(T_(2)))^(4)` |
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| 166. |
A black body radiates energy at the rate of E `W//m` at a high temperature TK . When the temperature is reduced to `(T)/(2)K` , the radiant energy will bA. `(E)/(16)`B. `(E)/(4)`C. 4ED. 16E |
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Answer» Correct Answer - A |
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| 167. |
The temperature at which a black body ceases to radiate energy is .A. `0 K`B. `273 K`C. `-273 k`D. at all temperatures |
| Answer» Correct Answer - A | |
| 168. |
A black body radiates at the of W watts at a temperture T. If the temperature of the body is reduced to `T//3`, it will radiate at the rate of (in Watts)A. `(W)/(81)`B. `(W)/(27)`C. `(W)/(9)`D. `(W)/(3)` |
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Answer» Correct Answer - A |
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| 169. |
Two spheres P and Q , of same colour having radii 8cm and 2cm are maintained at temperatures of `127^(@)C `. If temperature is increased to `927^(@)C`, then it radiates energy at the rate ofA. 0.054B. 0.0034C. 1D. 2 |
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Answer» Correct Answer - C |
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| 170. |
The ratio of energy of emitted radiation of a black body at `27^(@)C` and `927^(@)C` isA. `1 : 4`B. `1 : 16`C. `1 : 64`D. `1 : 256` |
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Answer» Correct Answer - D |
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| 171. |
Temperature of a black body increases from `327^(@)C` to `927^(@)C`, the initial energy possessed is 2KJ, what is its final energyA. 32 KJB. 320 KJC. 1200 JD. None of these |
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Answer» Correct Answer - A |
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| 172. |
A body radiates energy 5 W at a temperature of `127^(@)C` . If the temperature is increased to `927^(@)C`, then it radiates energy at the rate ofA. 410 WB. 81 WC. 405 WD. 200 W |
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Answer» Correct Answer - c |
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| 173. |
A black body radiates energy at the rate of `1 xx 10 J // s xx m` at temperature of `227 ^(@)C`, The temperature to which it must be heated so that it radiates energy at rate of `1 xx 10 J//sm`, isA. 5000 KB. 5000 CC. 500 KD. 500 C |
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Answer» Correct Answer - A |
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| 174. |
Power radiated by a black body is `P_0` and the wavelength corresponding to maximum energy is around `lamda_0`, On changing the temperature of the black body, it was observed that the power radiated becames `(256)/(81)P_0`. The shift in wavelength corresponding to the maximum energy will beA. `(lambda_(0))/(4)`B. `(lambda_(0))/(2)`C. `(lambda_(0))/(4)`D. `(lambda_(0))/(2)` |
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Answer» Correct Answer - C `lambda_(m)T =` const and `P = sigmaAT^(4), Deltalambda = lambda - lambda_(0)` |
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| 175. |
At `127^(@)C` radiates energy is `2.7 xx 10 J//s`. At what temperature radiated energy is `4.32 xx 10 J//s`A. 400 KB. 4000 KC. 80000 KD. 40000 K |
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Answer» Correct Answer - C |
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| 176. |
The power radiated by a black is `P` and it radiates maximum energy around the wavelength `lambda_(0)` If the temperature of the black body is now changed so that it radiates maximum energy around a wavelength `3lambda_(0)//4` the power radiated by it will increase by a factor of .A. `4//3`B. `16//9`C. `64//27`D. `256//81` |
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Answer» Correct Answer - D `P=sigmaAT^(4)` and `lambda_(m)T=const(P_(2))/(P_(1))=((T_(2))/(T_(1)))^(4)` |
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| 177. |
A spherical black body with a radius of `12cm` radiates `450W `power at `500K`. If the radius were halved and the temperature doubled, the power radiated in watt would beA. `225`B. `450`C. `900`D. `1800` |
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Answer» Correct Answer - D `P = sigmaAT^(4) rArr P =sigma (4piR^(2))T^(4)` `(P_(1))/(P_(2))=((R_(1))/(R_(2)))^(2)xx((T_(1))/(T_(2)))^(4)` . |
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| 178. |
A spherical black body with a radius of `12cm` radiates `450W `power at `500K`. If the radius were halved and the temperature doubled, the power radiated in watt would beA. 225B. 450C. 900D. 1800 |
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Answer» Correct Answer - D |
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| 179. |
Three rods of same dimensions are arranged as shown in Fig. They have thermal conductivities `K_1`,`K_2` and `K_3`. The points P and Q are maintained at different temeperature for the heat to flow at the same rate along PRQ and PQ. Whi of the following options correct?A. `K_(3)=(1)/(2)(K_(1)+K_(2))`B. `K_(3)=K_(1)+K_(2)`C. `K_(3)=(K_(1)K_(2))/(K_(1)+K_(2))`D. `K_(3)=2(K_(1)+K_(2))` |
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Answer» Correct Answer - C |
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| 180. |
A body is cooled in 2 min n a room at temperature of `30^@C` from `75^@C` to `65^@C`. If the same body Is cooled from `55^@C` to `45^@C` in the same room, find the time taken (in minute).A. 4B. 5C. 6D. 7 |
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Answer» Correct Answer - A |
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| 181. |
A room at `20^@C` is heated by a heater of resistence 20 ohm connected to 200 VV mains. The temperature is uniform throughout the room and the heati s transmitted through a glass window of area `1m^2` and thickness 0.2 cm. Calculate the temperature outside. Thermal conductivity of glass is `0.2 cal//mC^@` s and mechanical equivalent of heat is `4.2 J//cal`.A. `15.24^(@)C`B. `15.00^(@)C`C. `24.15^(@)C`D. None of the above |
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Answer» Correct Answer - A |
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| 182. |
There is formation of layer of snow x cm thick on water, when the temperature of air is `-theta^(@)C` (less than freezing point). The thickness of layer increases from x to y in the time r, then the value of t is given byA. `((x+y)(x-y)rhoL)/(2ktheta)`B. `((x-y)rhoL)/(2ktheta)`C. `((x+y)(x-y)rhoL)/(ktheta)`D. `((x-y)rhoLk)/(2theta)` |
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Answer» Correct Answer - A |
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| 183. |
A black body is at a temperature `300 K`. It emits energy at a rate, which is proportional toA. 300B. `(300)^(2)`C. `(300)^(3)`D. `(300)^(4)` |
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Answer» Correct Answer - D |
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| 184. |
Two metal plates of same area and thickness `l_(1)` and `l_(2)` are arranged in series If the thermal conductivities of the materials of the two plates are `K_(1)` and `K_(2)` The thermal conductivity of the combination is .A. `(2K_(1)K_(2))/(K_(1)+K_(2))`B. `(K_(1)+K_(2))/(2)`C. `(K_(1)K_(2)(l_(1)+l_(2)))/(K_(1)l_(2)+K_(2)l_(2))`D. `K_(1)+K_(2)` |
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Answer» Correct Answer - C `R_(eff)=R-(1)+R_(2)(R=(l)/(KA)),(l_(1)+l_(2))/(K_(eff))=(l_(1))/(k_(1))+(l_(2))/(k_(2))` |
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| 185. |
The ratio of the diameters of two metallic rods of the same material is `2 : 1` and their lengths are in the ratio `1 : 4`. If the temperature difference between their ends are equal, the rate of flow of heat in them will be in the ratio |
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Answer» Correct Answer - `16 : 1` |
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| 186. |
The lengths and radii of two rods made of same material are in the ratios 1 : 2 and 2 : 3 respectively. If the temperature difference between the ends for the two rods be the same, then in the steady state, the amount of heat flowing per second through them will be in the ratioA. `1 : 3`B. `4 : 3`C. `8 : 9`D. `3 : 2` |
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Answer» Correct Answer - C |
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| 187. |
Gulab jamuns (assumed to be spherical) are to be heated in on oven They are available in two sizes, one twice bigger (in radius) than the other Pizzas (assumed to discs) are also to be heated ibn oven They are also in two sizes, one twice bigger (in radius) than the other All four are put together to be heated option to oven temperature. Choose the correct option from the following .A. Both size gulab jamuns will get heated in the same timeB. Smaller gulab jamuns are heated before bigger onesC. Smaller pizzas are heated before bigger onesD. Bigger pizzas heated before bigger ones |
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Answer» Correct Answer - B::C The object having less surface area will be heated first because of less heat radiation . |
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| 188. |
A block of steel heated to `100^(@)C` is left in a room to cool Which of the curves shown in the represents the correct behaviour .A. `A`B. `B`C. `C`D. `A` and `C` |
| Answer» Correct Answer - A | |
| 189. |
For proper ventilation of building, windows must be open near the bottom and top of the walls so as to let passA. In more airB. In cool air near the bottom and hot air out near the roofC. In hot air near the roof and cool air out near the bottomD. Out hot air near the roof |
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Answer» Correct Answer - B |
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| 190. |
A heated object (at time `t=0` and temperature `T=T_(0))` is taken out of the oven to cool and placed on a table near an open window Write an expression for its temperature as function of time `T` where `T_(s)` is the surrounding temperature .A. `T=T_(s)-(T_(0)+T_(s))e^(-kt)`B. `T=T_(s)+(T_(0)+T_(s))e^(-kt)`C. `T=T_(s)+(T_(0)-T_(s))e^(-kt)`D. `T=T_(s)-(T_(0)-T_(s))e^(-kt)` |
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Answer» Correct Answer - C `(d theta)/(dt) =-K (T -T_(s))` `underset(T_(0))overset(T)int(d theta)/(T -T_(s)) = -K underset(0)overset(t)intdt log ((T-T_(s))/(T_(0)-T_(s)))=-Kt+C` . |
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| 191. |
Assertion : Woollen clothes keep the body warm in winter Reason : Air is a bad conductor of heat.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. |
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Answer» Correct Answer - A |
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| 192. |
A cylinder of radius `R` made of a material of thermal conductivity `K_(1)` is surrounded by cylindrical shell of inner radius `R` and outer radius `2R` made of a material of thermal con-ductivity `K_(2)` The two ends of the combined system are maintained at two differnet tem-peratures There is no loss of heat across the cylindrical surface and system is in steady state What is the effective thermal conductivity of the system .A. `K_(1)+K_(2)`B. `(K_(1)K_(2))/(K_(1)+K_(2))`C. `(K_(1)+3K_(2))/(4)`D. `(K_(1)+8K_(2))/(9)` |
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Answer» Correct Answer - D Two rods are in parallel `K_(eff) (A_(1)+A_(2))=K_(1)A_(1)+K_(2)A_(2)` `A_(1)=piR^(2)` and `A_(2)= pi (9R^(2)-R^(2))` . |
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| 193. |
A cylinder of radius `R` made of a material of thermal conductivity `K_(1)` is surrounded by cylindrical shell of inner radius `R` and outer radius `2R` made of a material of thermal con-ductivity `K_(2)` The two ends of the combined system are maintained at two differnet tem-peratures There is no loss of heat across the cylindrical surface and system is in steady state What is the effective thermal conductivity of the system . |
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Answer» `A_(1) = pi R^(2) ,A_(2) = pi (4R^(2) -R^(2))` Two cylinders are in parallel `:. K_(eff) (A_(1)+A_(2)) =K_(1) A_(1) +K_(2) A_(2)` `K_(eff) =(K_(1)piR^(2)+K_(2)3piR^(2))/(piR^(2)+3piR^(2)),i.eK_(eff) = ((K_(1)+3K_(2)))/(4)` . |
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| 194. |
The thermal conductivity of a material in CGS system is 0.4. In steady state, the rate of flow of heat 10 cal/sec-cm, then the thermal gradient will beA. `10^(@)C//cm`B. `12^(@)C//cm`C. `25^(@)C//cm`D. `20^(@)C//cm` |
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Answer» Correct Answer - C |
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| 195. |
A cylinder of radius `R` made of a material of thermal conductivity `K_(1)` is surrounded by cylindrical shell of inner radius `R` and outer radius `2R` made of a material of thermal con-ductivity `K_(2)` The two ends of the combined system are maintained at two differnet tem-peratures There is no loss of heat across the cylindrical surface and system is in steady state What is the effective thermal conductivity of the system .A. `K_(1)+K_(2)`B. `(K_(1)K_(2))/(K_(1)+K_(2))`C. `(K_(1)+3K_(2))/(4)`D. `(3K_(1)+K_(2))/(4)` |
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Answer» Correct Answer - c |
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| 196. |
Assertion : The S.I. unit of thermal conductivity is watt `m ^(1)1 K^(1)`. Reason : Thermal conductivity is a measure of ability of the material to allow the passage of heat through it.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. |
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Answer» Correct Answer - B |
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| 197. |
If the temperature of the sun becomes twice its present temperature, thenA. Radiated energy would be predominantly in infraredB. Radiated energy would be predominantly in ultravioletC. Radiated energy would be predominantly in X-ray regionD. Radiated energy would become twice the present radiated energy |
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Answer» Correct Answer - B |
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| 198. |
A sphare II A cube III A thin circular plate All made of the same material having the same mass are initially heated to `200^(@)C` Identify the order in which the objects cool faster when left in air room temperature ? .A. III,II and IB. II,I and IIIC. I, II and IIID. II,III and I |
| Answer» Correct Answer - A | |
| 199. |
A sphere and a cube of same material and same volume are heated up to same temperature and allowed to cool in the same sorroundings. The radio of the amounts of radiations emitted in equal time intervals will beA. `1:1`B. `(4pi)/(3):1`C. `((pi)/(6))^(1//3):1`D. `(1)/(2)((4pi)/(3))^(2//3):1` |
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Answer» Correct Answer - C Given, `("Volume")_("sphere")=("Volume")_("cube")` `(4)/(30 pi R^(30 =a^(3) rArr (R )/(a) =((3)/(4pi))^(⅓)` Here, `R` a are radius of this sphere and side of the cube `P=esigmaA(T^(4)-T_(S)^(4))rArr(P_(1))/(P_(2))=(A_(1))/(A_(2))=(4piR^(2))/(6a^(2))` . |
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| 200. |
A sphere a cube and thin circular plate, all made of the same material and having the same mass are initially heated to a temperature of `1000^(@)C`. Which one of these will cool first?A. Plate will cool fastest and cube the slowestB. Sphere will cool fastest and cube the slowestC. Plate will cool fastest and sphere the slowestD. Cube will cool fastest and plate the slowest . |
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Answer» Correct Answer - C As three objectes have same volume as per given case, the object having more surface area will radiate nore heat . |
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