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The correct choice is (b) False

The best explanation: THERMAL radiation from a body shows a CONTINUOUS spectrum of WAVELENGTHS. But at a given TEMPERATURE there is a particular short range of wavelengths which contributes the maximum to the total radiant energy. The graph given below shows the intensity of different wavelengths at different temperatures.

The correct answer is (b) False

The best explanation: Temperature is a relative MEASURE. When we touch a BODY we say it is hold or cold. We use devices like thermometers to indicate temperatures but we don’t have any FIXED ABSOLUTE value. When we say that temperature is 25°, it is relative to a reference we have DECIDED like steam point and ice point.

The correct option is (b) Time RATE of heat flow for a given temperature difference

For explanation I would say: Heat transfer by conduction occurs due to an INITIAL temperature difference. Heat flow per unit time for a given temperature difference can be a QUANTITATIVE description of heat flow by conduction. Note that temperature difference causes heat flow and not the other way AROUND.

The correct ANSWER is (b) Refreezing of ice on reduction in pressure

To EXPLAIN: When increase in pressure causes water to MELT. It may refreeze on removal of this extra pressure. This refreezing is CALLED RELEGATION.

The correct choice is (a) True

Easy explanation: Melting point is less for higher PRESSURE. For EG: we can keep a SMALL weight of 1kg on a block of ICE and we will SEE that the ice underneath the block starts melting at a lower temperature.

Correct answer is (b) -20°C

For EXPLANATION: LET the initial temperature of ice be T°C.HEAT lost by ice will be the same as the heat lost by water.

∴ 1*0.5*(0-T) + 1*80 = 9*1*10⇒ T = -20°C.

Right ANSWER is (a) B = 1.5A

To EXPLAIN: Let the coefficient of LINEAR EXPANSION be α.The coefficient of area expansion is 2α and the coefficient of volume expansion is 3α.∴ The coefficient of volume expansion is 1.5 times the coefficient of area expansion∴ B=1.5A.

Correct answer is (B) False

To EXPLAIN: To make steam, water has to be BOILED and then more heat energy has to be ADDED to convert it into steam. So, steam is more dangerous than boiling water.

Correct option is (a) True

Easy EXPLANATION: The temperature change with heat supplied is SHOWN below. During change of phase heat supplied is used to MAKE changes in intermolecular distances while the temperature remains CONSTANT.

Right option is (a) 2α

For explanation: The AREA(A) of a SPHERE is 4πr^2.When the temperature INCREASES by ΔT, let CHANGE in areabe dA.Let the radius INCREASE by dr.The coefficient of area expansion is (dA/A)/ΔT.

∴ dA = 4π(r – dr)^2– 4πr^2 ≅ 8πrdr.

Also, dr = rαΔT.

The coefficient of area expansion is (dA/A)/ΔT

= (8πr*rαΔT/4π) / ΔT

= 2α.

Right option is (b) False

The explanation is: Specific heat capacity is DEFINED as the heat capacity per unit MASS for a SUBSTANCE.s = ΔQ/mΔT.So, no matter what mass of a substance we take‘s’ will be equal to (ΔQ/ΔT) divided by that mass,which MEANS ‘s’ doesn’t depend on the mass.

Right choice is (d) It is the temperature at which an IDEAL gas will have zero pressure, assuming it stays a gas

Easiest EXPLANATION: Absolute zero has been defined as the temperature at which an ideal gas would have zero pressure, assuming it remains a gas TILL then. The temperature value is obtained by extrapolating the graph of Pressure vs Temperature till the straight line cuts the temperature axis. This gives US a value of -273.15°C. NOTE that this temperature hasn’t been achieved yet.

The CORRECT answer is (b) 25min

The explanation is: Average temperature of liquid in the first case = 60℃.

Rate of FALL of temperature =65-55 / 5 = 2°C /min.

Which is also equal to k(60 – 35) = 25k, where k is a constant.

∴ 25k = 2 Or k = 2/25

Average temperature in the second case = 40°C

Rate of fall of temp = 45 – 35 / t = k(40-35)

∴ t = 25mins.

The correct OPTION is (b) False

The EXPLANATION is: The graph of temperature difference with time given below shows that as temperature decreases rate of cooling (or temperature difference per unit time) ALSO decreases. We can see that for the same time INTERVAL temperature difference BECOMES less at lower temperatures.

The correct CHOICE is (a) Radiation doesn’t require any medium

The explanation: Radiation doesn’t require any medium for TRANSFER of heat. When a cooking pan is heated over a GAS stove, conduction is the PROCESS responsible for transfer of heat from flame to pan. Radiation involves electromagnetic waves transferring energy called radiant energy.

Correct option is (b) We actually measure the pressure at constant VOLUME and the scale is calibrated to give the temperature reading

Easy explanation: A constant volume gas thermometer has a MERCURY manometer connected to a gas bulb. With increase in temperature of the bulb, its volume is kept constant by external METHODS and the pressure of gas increases.The temperature scale is DEFINED as a function of this pressure.(T = kP, where k is a constant).

The correct CHOICE is (a) Ice will melt faster on the ALUMINIUM block

Easy explanation: Ice will melt faster on the aluminium block because it has a higher thermal CONDUCTIVITY than PLASTIC and hence conducts HEAT more rapidly than plastic. Which is why ice melts faster on aluminium.

Correct option is (b) It SHOWS linear variation in volume with temperature

Explanation: For measuring temperature in a thermometer we need a substance whose physical PROPERTIES change with temperature and can be easily RELATED with temperature. Mercury’s volume increases linearly with INCREASE in temperature and hence we can create a SCALE on the thermometer accordingly.

Correct option is (a) 122.4W

To EXPLAIN I WOULD say: The BODY will RECEIVE some energy from the surrounding and also lose some to it.

The net energy RECEIVED will be

= AeσT^4 – AeσTS^4

= 2*0.4*5.67*10^-8(333^4 – 313^4)

= 122.4 W.

Right choice is (d) Stay nonuniform

For EXPLANATION I would SAY: When a rod is held with one end in fire. That end will have a temperature equal to that of fire. The temperature will gradually decrease towards the other end. At steady STATE the rate of heat flow will be constant and temperature at each point will be constant, but will be varying non-uniformly through the LENGTH of the rod.

Correct CHOICE is (a) 63°C

To ELABORATE: TEMPERATURE at the fixed ends of both RODS will be the same.

KS AS (T-0)/LS = KC AC (100-T)/ LC

∴ 50*1/2 LCT = 384* C (100-T)

⇒ 25T = 38400 – 384T

⇒ T = 63°C.

Right answer is (b) False

Best explanation: The coefficient of thermal expansion is constant over a range of TEMPERATURE, but is not always constant. It DEPENDS on temperature. For eg: the GRAPH of coefficient of volume expansion of copper with temperature is shown below.

Correct ANSWER is (a) All LOW density gases show the same expansion behaviour

Explanation: It has been experimentally shown that low density gases show similar expansion behaviour. If we keep the gas’s VOLUME constant pressure increases monotonically with increasing temperature. HENCE, we can use any low density gas for a constant volume gas thermometer.

Correct answer is (B) False

To EXPLAIN: NEWTON’s law of cooling can only be USED when the temperature difference is small which is not the case in the given scenario. So, the given STATEMENT is false.

Right CHOICE is (c) 0.0821 L ATM mol^-1K^-1

Explanation: The value of universal gas CONSTANT is 0.0821 L atm mol^-1K^-1.Or it is 8.314 J mol^-1K^-1.The constant in PV/T = constant depends on the number of moles taken.

Correct answer is (a) True

To explain I would say: Boyle’s and Charle’s law are used to ARRIVE at the ideal gas law. And the ideal gas law is based on the ASSUMPTIONS of kinetic THEORY of gases, which are only valid for LOW density gases. For eg: the assumption that molecules exert no forces on each other can only be considered for low density.

The correct OPTION is (a) AσT^4Δt, in UNIT time Δt

The EXPLANATION: The relation of ENERGY is given by Stefan-Boltzman law:Energy per unit time = AσT^4, where σ is called the Stefan-Boltzman constant.∴ Energy =AσT^4Δt, in unit time Δt.

The correct choice is (d) It requires heat to be supplied to the SUBSTANCE

Easy explanation: Melting is the CONVERSION of solid to liquid at constant temperature. It is endothermic and the melting temperature varies from substance to substance and also on atmospheric CONDITIONS like pressure.

The CORRECT option is (a) True

To explain I would say: Condensation is the CONVERSION of vapour to liquid, while evaporation is the conversion of liquid to vapour. Both occur at the same temperature, the only DIFFERENCE being that heat is removed in the former and added in the latter. The graph as shown below is a straight LINE at constant temperature.

Correct CHOICE is (a) 13.3K

For explanation I WOULD say: no. of MOLES of neon gas = pV/RT

= (1.3*10^5*0.6) / (8.31*200)

= 46.9 moles ≅ 47 moles

ΔQ = nCVΔTΔT = ΔQ/nCV

= (8360/4.18) / (47*3.2)

= 13.3K.

The correct ANSWER is (C) 1.25

To EXPLAIN: CP = CV + R = 8 + 2

= 10 calK^-1mol^-1.

CP/CV= 10 / 8 = 1.25.

Correct answer is (a) Increases

Best explanation: BOILING occurs when vapour pressure of liquid is the same as atmospheric pressure. The vapour pressure increases with increase in temperature. So when temperature has been INCREASED sufficiently boiling starts. But with increase in pressure at HIGHER vapour pressure has to be REACHED which is obtained by INCREASING temperature and therefore we say boiling point increases.

Right answer is (a) It is the HEAT required to RAISE the temperature of 1g of water from 14.5°C to 15.5°C at 760mm Hg

Easy explanation: A CALORIE is the unit of energy and is defined as the amount of heat required to raise the temperature of 1g of water from 14.5°C to 15.5°C at 760mm Hg.Its VALUE is 4.18 joules.Note that the calories we read behind food packets correspond to the amount of heat that quantity of food provides to our BODY which it uses for functioning.

Right choice is (b) The total heat lost by a HOT body is same as the total heat gained by the cold body provided no heat is lost to the surroundings

To elaborate: The principle of calorimeter STATES that heat lost by a hot body is the same as the heat gained by the cold body provided no heat is lost to the surroundings. The other statement that states that the AMOUNT of heat flow from a sample to TWO different samples of same mass is a product of their specific heats and temperature difference is true but it is not the principle of CALORIMETRY. It is just a mathematical way of understanding heat transfer.

Correct option is (a) PV/T = constant

For explanation: BOYLE’s law states that P ∝ 1/V.Charle’s law states that V ∝ T.

From this we can say thatV ∝ T/P OR PV/T = constant.Note that this is the ideal GAS law.

Right option is (a) Its SIZE increases

The explanation: The hole’s circumference is made of metal. When the sheet is heated this circular circumference will EXPAND and THEREFORE the size of hole will INCREASE. The hole will not get deformed as the sheet is uniform in all directions from the centre of hole and is also heated uniformly.

The correct OPTION is (b) 80.6°F

The explanation is: TEMPERATURE in K = 273 + temp in °C.

∴ Temp in °C = 300-273 = 27

°F = (9/5) °C + 32

= (9/5)*27 + 32

= 80.6°F.

The correct CHOICE is (C) 6

Easiest explanation: For changing a solid into liquid, HEAT has to be supplied and this change occurs at constant temperature.Q = mL

⇒ 30 = 5L

⇒ L = 6 cal/g,

Right answer is (a) 2.9*10^-3mK

The BEST explanation: Wein’s displacement law states that the PRODUCT of temperature and wavelength CONTRIBUTING the most to ENERGY is a constant equal to 2.9*10^-3mK.