Practice Test


1) The thermal resistance of two block connected in series, if their separate thermal resistances are 2 and 3, is


2) Woolen clothes are used in winter season because woolen clothes


3) Only a very small fraction of the energy supplied to a domestic light bulb is emitted as light. This is because


4) The thermal conductivity of copper decreases significantly as the temperature is increased. This is because, at higher temperatures,


5) The dimensional formula of thermal resistance is


6) An unlagged cubic tank containing hot water loses heat to its surroundings at a rate of 900 W. This loss is reduced at 60 W, if all the faces of tank are covered with a layer of lagging. What will be the rate of loss of heat if one face is left unlagged? (the temperatures of the water and surroundings are unaltered. You may assume that heat is lost only from faces and that the rate of loss of heat from a face is unaffected by whether it is vertical or horizontal, top or bottom).


7) 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 that


8) A partition wall has two layers A and B in contact, each made of a different material. They have the same thickness but the thermal conductivity of layer A is twice that of layer B. If the steady state temperature difference across the wall is 60 K, then the corresponding difference across the layer A is


9) Statement 1 : For steady state during heat conduction across a rod of uniform cross-section temperature gradient is small for all points.
Statement 2 : Thermal current decreases as we move across rod from higher temperature to lower temperature.


10) Statement 1 : Thermal current is same at all points in a conductor of uniform cross-section during steady state.
Statement 2 : Thermal current is proportional to cross sectional area of conductor for a given temperature difference across conductor.


11) Which of the following statements regarding thermal radiation is not correct?


12) On heating one end of a rod, the temperature of the whole rod will be uniform when


13) Heat travels through vacuum by


14) Two friends A and B are waiting for another friend for tea. A took the tea in a cup and mixed the cold milk and then waited. B took the tea in the cup and then mixed the cold milk when the friend comes. Then the tea will be hotter in the cup of


15) When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time, every point of the rod attains a constant temperature, then


16) When the filament of a light bulb is heated slowly, its colour changes from red to orange to yellow and eventually to white. It never appears green or blue. This is because


17) A certain bolometer detects thermal radiation by the change of resistance of a metal foil when exposed to the radiation. In order to have a bolometer of high sensitivity and rapid response, it is desirable that the foil should have


18) Two cylindrical rods of the same material have the same temperature difference between their ends. The ratio of the rates of flow of heat through them is 1 : 8. The radii of the rods are in the ratio 1 : 2. What is the ratio of their lengths?


19) 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


20) Two vessels of different material are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 30 minutes. The ratio of their thermal conductivities will be


21) The temperature of a liquid drops from 365 K to 36 K in 2 minutes. The time during which temperature of the liquid drops from 344 K to 342 K is (Temperature of room is 293 K)


22) If black wire of platinum is heated, then its colour first appears red, then yellow and finally white. It can be understood on the basis of


23) In cold countries, householders are being urged to reduced heat loss from roofs by laying a matting of fiber-glass, which consists of a very large number of intertwined fine glass fibers, on the roof space. The principal reason why fiber-glass is effective as a heat insulator is that


24) Statement 1 : In distribution of energy in spectrum of black body at given temperature, energy is not distributed uniformly among different wavelengths.
Statement 2 : For all wavelengths increase in temperature causes a decrease in intencity.


25) Statement 1 : According to Kirchoff's law, bad absorber is bad emitter.
Statement 2: Bad emitter is bad reflector.


26) Temperature of B junction is


27) Heat current in AB is


28) Ratio of thermal resistance of BC to AC


29) In which case the thermal conductivity increases from left to right


30) Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature


31) The heat is flowing through two cylindrical rods of same material. The diameters of the rods are in the ratio 1 : 2 and their lengths are in the ratio 2 : 1. If the temperature difference between their ends is the same, the ratio of rate of flow of heat through them will be


32) For cooking the food, which of the following type of utensil is most suitable


33) Under steady state, the temperature of a body


34) The coefficient of thermal conductivity depends upon


35) When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time every point of the rod attains a constant temperature, then


36) 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 ratio


37) Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 30 minutes. The ratio of their thermal conductivities will be


38) In variable state, the rate of flow of heat is controlled by


39) If the ratio of coefficient of thermal conductivity of silver and copper is 10 : 9, then the ratio of the lengths upto which wax will melt in Ingen Hausz experiment will be


40) In Searle's method for finding conductivity of metals, the temperature gradient along the bar


41) The dimensions of thermal resistance are


42) A piece of glass is heated to a high temperature and then allowed to cool. If it cracks, a probable reason for this is the following property of glass


43) On heating one end of a rod, the temperature of whole rod will be uniform when


44) Snow is more heat insulating than ice, because


45) Two thin blankets keep more hotness than one blanket of thickness equal to these two. The reason is


46) Ice formed over lakes has


47) Two rods of same length and material transfer a given amount of heat in 12 seconds, when they are joined end to end. But when they are joined lengthwise, then they will transfer same heat in same conditions in


48) 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


49) If the radius and length of a copper rod are both doubled, the rate of flow of heat along the rod increases


50) The quantity of heat which crosses unit area of a metal plate during conduction depends upon


51) Two spheres of different materials one with double the radius and one-fourth wall thickness of the other, are filled with ice. If the time taken for complete melting ice in the large radius one is 25 minutes and that for smaller one is 16 minutes, the ratio of thermal conductivities of the materials of larger sphere to the smaller sphere is


52) 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


53) 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 and respectively. If thermal conductivity of copper is 0.92, then thermal conductivity of iron is


54) Mud houses are cooler in summer and warmer in winter because


55) On a cold morning, a metal surface will feel colder to touch than a wooden surface because


56) In order that the heat flows from one part of a solid to another part, what is required


57) 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 are


58) 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 is


59) 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 ratio


60) There are two identical vessels filled with equal amounts of ice. The vessels are of different metals., If the ice melts in the two vessels in 20 and 35 minutes respectively, the ratio of the coefficients of thermal conductivity of the two metals is


61) 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 is


62) Heat current is maximum in which of the following (rods are of identical dimension)


63) Consider a compound slab consisting of two different materials having equal thickness and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is


64) Woollen clothes are used in winter season because woolen clothes


65) The ratio of the coefficient of thermal conductivity of two different materials is 5 : 3. If the thermal resistance of the rod of same thickness resistance of the rods of same thickness of these materials is same, then the ratio of the length of these rods will be


66) It is hotter for the same distance over the top of a fire than it is in the side of it, mainly because


67) One likes to sit under sunshine in winter season, because


68) Air is bad conductor of heat or partly conducts heat, still vacuum is to be placed between the walls of the thermos flask because


69) While measuring the thermal conductivity of a liquid, we keep the upper part hot and lower part cool, so that


70) For proper ventilation of building, windows must be open near the bottom and top of the walls so as to let pass


71) The layers of atmosphere are heated through


72) Mode of transmission of heat, in which heat is carried by the moving particles, is


73) In a closed room, heat transfer takes place by


74) In heat transfer, which method is based on gravitation


75) When fluids are heated from the bottom, convection currents are produced because


76) If a liquid is heated in weightlessness, the heat is transmitted through


77) The rate of loss of heat from a body cooling under conditions of forced convection is proportional to its (A) heat capacity (B) surface area (C) absolute temperature (D) excess of temperature over that of surrounding : state if


78) In which of the following process, convection does not take place primarily


79) On a clear sunny day, an object at temperature T is placed on the top of a high mountain. An identical object at the same temperature is placed at the foot of mountain. If both the objects are exposed to sun-rays for two hours in an identical manner, the object at the top of the mountain will register a temperature


80) In which process, the rate of transfer of heat is maximum


81) Which of the following is the correct device for the detection of thermal radiation


82) A thermos flask is polished well


83) Heat travels through vacuum by


84) The energy supply being cut-off, an electric heater element cools down to the temperature of its surroundings, but it will not cool further because


85) We consider the radiation emitted by the human body. Which of the following statements is true


86) The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by


87) Infrared radiation is detected by


88) Pick out the statement which is not true


89) A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body


90) Good absorbers of heat are


91) For a perfectly black body, its absorptive power is


92) As compared to the person with white skin, the person with black skin will experience


93) Which of the following statements is wrong


94) Half part of ice block is covered with black cloth and rest half is covered with white cloth and then it is kept in sunlight. After some time clothes are removed to see the melted ice. Which of the following statements is correct


95) Distribution of energy in the spectrum of a black body can be correctly represented by


96) In rainy season, on a clear night the black seat of a bicycle becomes wet because


97) There is a rough black spot on a polished metallic plate. It is heated upto 1400 K approximately and then at once taken in a dark room. Which of the following statements is true


98) At a certain temperature for given wave length, the ratio of emissive power of a body to emissive power of black body in same circumstances is known as


99) The cause of Fraunhoffer lines is


100) Two thermometers A and B are exposed in sun light. The valve of A is painted black, But that of B is not painted. The correct statement regarding this case is


101) There is a black spot on a body. If the body is heated and carried in dark room then it glows more. This can be explained on the basis of


102) When red glass is heated in dark room it will seem


103) A hot body will radiate heat most rapidly if its surface is


104) A body, which emits radiations of all possible wavelengths, is known as


105) Which of the following is the example of ideal black body


106) An ideal black body at room temperature is thrown into a furnace. It is observed that


107) Absorption co-efficient of an open window is


108) Which of the prism is used to see infra-red spectrum of light


109) Which of the following statement is correct


110) A piece of blue glass heated to a high temperature and a piece of red glass at room temperature, are taken inside a dimly lit room then


111) Which of the following law states that “good absorbers of heat are good emitters”


112) According to Wein's law


113) 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 that


114) The wavelength of radiation emitted by a body depends upon


115) If black wire of platinum is heated, then its colour first appear red, then yellow and finally white. It can be understood on the basis of


116) Colour of shining bright star is an indication of its


117) Two stars emit maximum radiation at wavelength 3600 and 4800 respectively. The ratio of their temperatures is


118) Four pieces of iron heated in a furnace to different temperatures show different colours listed below. Which one has the highest temperature


119) If a black body is heated at a high temperature, it seems to be


120) If the temperature of the sun becomes twice its present temperature, then


121) How is the temperature of stars determined by


122) On increasing the temperature of a substance gradually, which of the following colours will be noticed by you


123) Relation between the colour and the temperature of a star is given by


124) The absolute temperatures of two black bodies are 2000 K and 3000 K respectively. The ratio of wavelengths corresponding to maximum emission of radiation by them will be


125) The amount of radiation emitted by a perfectly black body is proportional to


126) If the temperature of the sun (black body) is doubled, the rate of energy received on earth will be increased by a factor of


127) Two black metallic spheres of radius 4m, at 2000 K and 1m at 4000 K will have ratio of energy radiation as


128) A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to


129) If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be


130) 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 is


131) Two spheres of same material have radius 1m and 4 m and temperature 4000K and 2000K respectively. The energy radiated per second by the first sphere is


132) The radiation emitted by a star A is 10,000 times that of the sun. If the surface temperatures of the sun and the star A are 6000 K and 2000 K respectively, the ratio of the radii of the star A and the sun is


133) A black body radiates at the rate of W watts at a temperature T. If the temperature of the body is reduced to T/3, it will radiate at the rate of (in Watts)


134) 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 emitted by it then will increase by a factor of


135) If the temperature of the sun were to be increased from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on the earth to what it was previously will be


136) If the initial temperatures of metallic sphere and disc, of the same mass, radius and nature are equal, then the ratio of their rate of cooling in same environment will be


137) If the temperature of the body is increased by 10%, the percentage increase in the emitted radiation will be


138) A sphere at temperature 600K is placed in an environment of temperature is 200K. Its cooling rate is H. If its temperature reduced to 400K then cooling rate in same environment will become


139) The value of Stefan’s constant is


140) Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is


141) When the body has the same temperature as that of surroundings


142) The ratio of radiant energies radiated per unit surface area by two bodies is 16 : 1, the temperature of hotter body is 1000K, then the temperature of colder body will be


143) The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is


144) Newton's law of cooling is a special case of


145) Equal masses of two liquids are filled in two similar calorimeters. The rate of cooling will


146) Which of the following statements is true/correct


147) The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if


148) The temperature of a liquid drops from 365 to 361 K in 2 minutes. Find the time during which temperature of the liquid drops from 344 K to 342 K . Temperature of room is 293 K


149) Newton’s law of cooling, holds good only if the temperature difference between the body and the surroundings is


150) According to ‘Newton’s Law of cooling’, the rate of cooling of a body is proportional to the


151) Two rods (one semi-circular and other straight) of same material and of same cross-sectional area are joined as shown in the figure. The points A and B are maintained at different temperature. The ratio of the heat transferred through a cross-section of a semi-circular rod to the heat transferred through a cross section of the straight rod in a given time is


152) A solid sphere and a hollow sphere of the same material and size are heated to the same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is T , then


153) llowing graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature


154) A block of metal is heated to a temperature much higher than the room temperature and allowed to cool in a room free from air currents. Which of the following curves correctly represents the rate of cooling


155) 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 by


156) Assertion :A body that is a good radiator is also a good absorber of radiation at a given wavelength.
Reason : According to Kirchoff’s law the absorptivity of a boy is equal to its emissivity at a given wavelength.


157) Assertion :For higher temperature, the peak emission wavelength of a black body shifts to lower wavelengths.
Reason : Peak emission wavelength of a blackbody is proportional to the fourth power of temperature.


158) Assertion:Temperatures near the sea coast are moderate.
Reason : Water has a high thermal conductivity.


159) Assertion:It is hotter over the top of a fire than at the same distance on the sides.
Reason : Air surrounding the fire conducts more heat upwards.


160) Assertion:Bodies radiate heat at all temperatures.
Reason : Rate of radiation of heat is proportional to the fourth power of absolute temperature.


161) Assertion:Woolen clothes keep the body warm in winter.
Reason : Air is a bad conductor of heat.


162) Assertion:A hollow metallic closed container maintained at a uniform temperature can act as a source of black body radiation.
Reason : All metals acts as a black body


163) Assertion:If the temperature of a star is doubled then the rate of loss of heat from it becomes 16 times.
Reason : Specific heat varies with temperature.


164) 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.


165) Assertion:A brass tumbler feels much colder than a wooden tray on a chilly day.
Reason : The thermal conductivity of brass is less than that of wood.


166) Assertion:Like light radiations, thermal radiations are also electromagnetic radiation.
Reason : The thermal radiations require no medium for propagation.


167) Assertion:Snow is better insulator than ice.
Reason : Snow contain air packet and air is good insulator of heat.


168) Assertion:Water can be boiled inside satellite by convection.
Reason : Convection is the process in which heat is transmitted from a place of higher temperature to a place of lower temperature by means of particles with their migrations from one place to another.


169) Assertion:The absorbance of a perfect black body is unity.
Reason : A perfect black body when heated emits radiations of all possible wavelengths at that temperature.


170) Assertion:As temperature of a black body is raised, wavelength corresponding to maximum energy reduces.
Reason : Higher temperature would mean higher energy and hence higher wavelength.


171) Assertion:All black coloured objects are considered black bodies.
Reason : Black colour is a good absorber of heat.


172) Assertion:Greater is the coefficient of thermal conductivity of a material, smaller is the thermal resistance of a rod of that material.
Reason : Thermal resistance is the ratio of temperature difference between the ends of the conductor and rate of flow of heat.


173) Assertion:Radiation is the speediest mode of heat transfer.
Reason : Radiation can be transmitted in zig-zag motion.


174) Assertion:Two thin blankets put together are warmer than a single blanket of double the thickness.
Reason : Thickness increases because of air layer enclosed between the two blankets.


175) Assertion:Animals curl into a ball, when they feel very cold.
Reason : Animals by curling their body reduces the surface area.


176) Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 40 minutes respectively. The ratio of thermal conductivities of the materials is


177) Four rods of silver, copper, brass and wood are of same shape. They are heated together after wrapping a paper on it, the paper will burn first on


178) Two friends A and B are waiting for another friend for tea. A took the tea in a cup and mixed the cold milk and then waits. B took the tea in the cup and then mixed the cold milk when the friend comes. Then the tea will be hotter in the cup of


179) There are two spherical balls A and B of the same material with same surface, but the diameter of A is half that of B. If A and B are heated to the same temperature and then allowed to cool, then


180) Can we boil water inside the earth satellite by convection


181) The spectrum from a black body radiation is a


182) The Wien’s displacement law express relation between


183) A partition wall has two layers A and B in contact, each made of a different material. They have the same thickness but the thermal conductivity of layer A is twice that of layer B . If the steady state temperature difference across the wall is 60 K , then the corresponding difference across the layer A is