Practice Test

Q1) The thermal resistance of two block connected in series, if their separate thermal resistances are 2 and 3, is Show Answer

Q2) Woolen clothes are used in winter season because woolen clothes Show Answer

Q3) Only a very small fraction of the energy supplied to a domestic light bulb is emitted as light. This is because Show Answer

Q4) The thermal conductivity of copper decreases significantly as the temperature is increased. This is because, at higher temperatures, Show Answer

Q5) The dimensional formula of thermal resistance is Show Answer

Q6) 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). Show Answer

Q7) 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 Show Answer

Q8) 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 Show Answer

Q9) 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. Show Answer

Q10) 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. Show Answer

Q11) Which of the following statements regarding thermal radiation is not correct? Show Answer

Q12) On heating one end of a rod, the temperature of the whole rod will be uniform when Show Answer

Q13) 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 Show Answer

Q14) 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 Show Answer

Q15) 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 Show Answer

Q16) 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 Show Answer

Q17) 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? Show Answer

Q18) 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 Show Answer

Q19) 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 Show Answer

Q20) 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) Show Answer

Q21) 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 Show Answer

Q22) 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 Show Answer

Q23) 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. Show Answer

Q24) Statement 1 : According to Kirchoff's law, bad absorber is bad emitter.
Statement 2: Bad emitter is bad reflector. Show Answer

Q25) Temperature of B junction is Show Answer

Q26) Heat current in AB is Show Answer

Q27) Ratio of thermal resistance of BC to AC Show Answer

Q28) In which case the thermal conductivity increases from left to right Show Answer

Q29) Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature Show Answer

Q30) 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 Show Answer

Q31) For cooking the food, which of the following type of utensil is most suitable Show Answer

Q32) Under steady state, the temperature of a body Show Answer

Q33) The coefficient of thermal conductivity depends upon Show Answer

Q34) 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 Show Answer

Q35) 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 Show Answer

Q36) 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 Show Answer

Q37) In variable state, the rate of flow of heat is controlled by Show Answer

Q38) 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 Show Answer

Q39) In Searle's method for finding conductivity of metals, the temperature gradient along the bar Show Answer

Q40) The dimensions of thermal resistance are Show Answer

Q41) 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 Show Answer

Q42) On heating one end of a rod, the temperature of whole rod will be uniform when Show Answer

Q43) Snow is more heat insulating than ice, because Show Answer

Q44) Two thin blankets keep more hotness than one blanket of thickness equal to these two. The reason is Show Answer

Q45) Ice formed over lakes has Show Answer

Q46) 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 Show Answer

Q47) 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 Show Answer

Q48) If the radius and length of a copper rod are both doubled, the rate of flow of heat along the rod increases Show Answer

Q49) The quantity of heat which crosses unit area of a metal plate during conduction depends upon Show Answer

Q50) 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 Show Answer

Q51) 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 Show Answer

Q52) 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 Show Answer

Q53) Mud houses are cooler in summer and warmer in winter because Show Answer

Q54) On a cold morning, a metal surface will feel colder to touch than a wooden surface because Show Answer

Q55) In order that the heat flows from one part of a solid to another part, what is required Show Answer

Q56) 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 Show Answer

Q57) 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 Show Answer

Q58) 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 Show Answer

Q59) 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 Show Answer

Q60) 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 Show Answer

Q61) Heat current is maximum in which of the following (rods are of identical dimension) Show Answer

Q62) 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 Show Answer

Q63) Woollen clothes are used in winter season because woolen clothes Show Answer

Q64) 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 Show Answer

Q65) It is hotter for the same distance over the top of a fire than it is in the side of it, mainly because Show Answer

Q66) One likes to sit under sunshine in winter season, because Show Answer

Q67) Air is bad conductor of heat or partly conducts heat, still vacuum is to be placed between the walls of the thermos flask because Show Answer

Q68) While measuring the thermal conductivity of a liquid, we keep the upper part hot and lower part cool, so that Show Answer

Q69) For proper ventilation of building, windows must be open near the bottom and top of the walls so as to let pass Show Answer

Q70) The layers of atmosphere are heated through Show Answer

Q71) Mode of transmission of heat, in which heat is carried by the moving particles, is Show Answer

Q72) In a closed room, heat transfer takes place by Show Answer

Q73) In heat transfer, which method is based on gravitation Show Answer

Q74) When fluids are heated from the bottom, convection currents are produced because Show Answer

Q75) If a liquid is heated in weightlessness, the heat is transmitted through Show Answer

Q76) 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 Show Answer

Q77) In which of the following process, convection does not take place primarily Show Answer

Q78) 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 Show Answer

Q79) In which process, the rate of transfer of heat is maximum Show Answer

Q80) Which of the following is the correct device for the detection of thermal radiation Show Answer

Q81) A thermos flask is polished well Show Answer

Q82) Heat travels through vacuum by Show Answer

Q83) 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 Show Answer

Q84) We consider the radiation emitted by the human body. Which of the following statements is true Show Answer

Q85) The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by Show Answer

Q86) Infrared radiation is detected by Show Answer

Q87) Pick out the statement which is not true Show Answer

Q88) 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 Show Answer

Q89) Good absorbers of heat are Show Answer

Q90) For a perfectly black body, its absorptive power is Show Answer

Q91) As compared to the person with white skin, the person with black skin will experience Show Answer

Q92) Which of the following statements is wrong Show Answer

Q93) 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 Show Answer

Q94) Distribution of energy in the spectrum of a black body can be correctly represented by Show Answer

Q95) In rainy season, on a clear night the black seat of a bicycle becomes wet because Show Answer

Q96) 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 Show Answer

Q97) 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 Show Answer

Q98) The cause of Fraunhoffer lines is Show Answer

Q99) 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 Show Answer

Q100) 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 Show Answer

Q101) When red glass is heated in dark room it will seem Show Answer

Q102) A hot body will radiate heat most rapidly if its surface is Show Answer

Q103) A body, which emits radiations of all possible wavelengths, is known as Show Answer

Q104) Which of the following is the example of ideal black body Show Answer

Q105) An ideal black body at room temperature is thrown into a furnace. It is observed that Show Answer

Q106) Absorption co-efficient of an open window is Show Answer

Q107) Which of the prism is used to see infra-red spectrum of light Show Answer

Q108) Which of the following statement is correct Show Answer

Q109) 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 Show Answer

Q110) Which of the following law states that “good absorbers of heat are good emitters” Show Answer

Q111) According to Wein's law Show Answer

Q112) 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 Show Answer

Q113) The wavelength of radiation emitted by a body depends upon Show Answer

Q114) 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 Show Answer

Q115) Colour of shining bright star is an indication of its Show Answer

Q116) Two stars emit maximum radiation at wavelength 3600 and 4800 respectively. The ratio of their temperatures is Show Answer

Q117) Four pieces of iron heated in a furnace to different temperatures show different colours listed below. Which one has the highest temperature Show Answer

Q118) If a black body is heated at a high temperature, it seems to be Show Answer

Q119) If the temperature of the sun becomes twice its present temperature, then Show Answer

Q120) How is the temperature of stars determined by Show Answer

Q121) On increasing the temperature of a substance gradually, which of the following colours will be noticed by you Show Answer

Q122) Relation between the colour and the temperature of a star is given by Show Answer

Q123) 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 Show Answer

Q124) The amount of radiation emitted by a perfectly black body is proportional to Show Answer

Q125) If the temperature of the sun (black body) is doubled, the rate of energy received on earth will be increased by a factor of Show Answer

Q126) Two black metallic spheres of radius 4m, at 2000 K and 1m at 4000 K will have ratio of energy radiation as Show Answer

Q127) A black body is at a temperature 300 K. It emits energy at a rate, which is proportional to Show Answer

Q128) If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be Show Answer

Q129) 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 Show Answer

Q130) 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 Show Answer

Q131) 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 Show Answer

Q132) 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) Show Answer

Q133) 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 Show Answer

Q134) 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 Show Answer

Q135) 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 Show Answer

Q136) If the temperature of the body is increased by 10%, the percentage increase in the emitted radiation will be Show Answer

Q137) 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 Show Answer

Q138) The value of Stefan’s constant is Show Answer

Q139) Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is Show Answer

Q140) When the body has the same temperature as that of surroundings Show Answer

Q141) 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 Show Answer

Q142) The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is Show Answer

Q143) Newton's law of cooling is a special case of Show Answer

Q144) Equal masses of two liquids are filled in two similar calorimeters. The rate of cooling will Show Answer

Q145) Which of the following statements is true/correct Show Answer

Q146) The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if Show Answer

Q147) 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 Show Answer

Q148) Newton’s law of cooling, holds good only if the temperature difference between the body and the surroundings is Show Answer

Q149) According to ‘Newton’s Law of cooling’, the rate of cooling of a body is proportional to the Show Answer

Q150) 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 Show Answer

Q151) 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 Show Answer

Q152) llowing graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature Show Answer

Q153) 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 Show Answer

Q154) 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 Show Answer

Q155) 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.
Show Answer

Q156) 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.
Show Answer

Q157) Assertion:Temperatures near the sea coast are moderate.
Reason : Water has a high thermal conductivity.
Show Answer

Q158) 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.
Show Answer

Q159) Assertion:Bodies radiate heat at all temperatures.
Reason : Rate of radiation of heat is proportional to the fourth power of absolute temperature.
Show Answer

Q160) Assertion:Woolen clothes keep the body warm in winter.
Reason : Air is a bad conductor of heat.
Show Answer

Q161) 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
Show Answer

Q162) 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.
Show Answer

Q163) 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.
Show Answer

Q164) 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.
Show Answer

Q165) Assertion:Like light radiations, thermal radiations are also electromagnetic radiation.
Reason : The thermal radiations require no medium for propagation.
Show Answer

Q166) Assertion:Snow is better insulator than ice.
Reason : Snow contain air packet and air is good insulator of heat.
Show Answer

Q167) 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. Show Answer

Q168) 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.
Show Answer

Q169) 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.
Show Answer

Q170) Assertion:All black coloured objects are considered black bodies.
Reason : Black colour is a good absorber of heat.
Show Answer

Q171) 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.
Show Answer

Q172) Assertion:Radiation is the speediest mode of heat transfer.
Reason : Radiation can be transmitted in zig-zag motion.
Show Answer

Q173) 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.
Show Answer

Q174) Assertion:Animals curl into a ball, when they feel very cold.
Reason : Animals by curling their body reduces the surface area.
Show Answer

Q175) 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 Show Answer

Q176) 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 Show Answer

Q177) 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 Show Answer

Q178) 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 Show Answer

Q179) Can we boil water inside the earth satellite by convection Show Answer

Q180) The spectrum from a black body radiation is a Show Answer

Q181) The Wien’s displacement law express relation between Show Answer

Q182) 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 Show Answer