**Q211. Statement 1: The expanded length l of a rod of original length l_0 is not correctly given by (assuming Î± to be constant with T) l=l_0 (1+Î±∆T) if a ∆T is large**

Statement 2: It is given by l=l_0 e^{Î±∆T}, which cannot be treated as being approximately equal to l=l_0 (1+Î±∆T) for large value a ∆T

**Q212. Statement 1: Like light radiations, thermal radiation are also electromagnetic radiation**

Statement 2: The thermal radiations require no medium for propagation

212(b) Light radiations and thermal radiations both belong to electromagnetic spectrum. Light radiations belong to visible region while thermal radiation belong to infrared region to EM spectrum. Also EM radiations requires no medium for propagation

**Q213. Statement 1: Greater is the coefficient of thermal conductivity of a material, smaller is the thermal resistance of a that material**

Statement 2: Thermal resistance is the ratio of temperature difference between the ends of the conductor and rate of flow of heat

213(b) (b) R=((Î¸_1-Î¸_2))/(Ï‰/t)=l/KA⇒R∝1/K

**Q214. Statement 1: As the temperature of the black body increases, the wavelength at which the spectral intensity (E_Î» ) is maximum decreases**

Statement 2: The wavelength at which the spectral intensity will be maximum for a black body is proportional to the fourth power of its absolute temperature

214 (c) From Wein’s law Î»_m T= constant i.e., peak emission wavelength Î»_m∝1/T. Hence as T increases Î»_m decreases

**Q215. Statement 1: The bulb of one thermometer is spherical while that of the other is cylindrical. Both have equal amounts of mercury. The response of the cylindrical bulb thermometer will be quicker**

Statement 2: Heat conduction in a body is directly proportional to cross-sectional area

215 (a) Both are true and Statement II explains Statement I because for same volume, surface area of the cylindrical bulb will be more

**Q216. Statement 1: Two solid cylindrical rods of identical size and different thermal conductivity K_1and K_2 are connected in series. Then the equivalent thermal conductivity of two rods system is less than that value of thermal conductivity of either rod**

Statement 2: For two cylindrical rods of identical size and different thermal conductivity K_1 and K_2 connected in series, the equivalent thermal conductivity K is given by 2/K=1/K_1 +1/K_2

216 (d) Equivalent thermal conductively of two identical rods in series is given by 2/K=1/K_1 +1/K_2 If K_1

**Q217. Statement 1: A body that is a good radiator is also a good absorber of radiation at a given wavelength**

Statement 2: According to Kirchoff’s law the absorptivity of a body is equal to its emissivity at a given wavelength

217 (a) According to Kirchoff’s law e_Î»/a_Î» =E_Î» For a particular wavelength E_Î»=1⇒e_Î»=a_Î» ∴ Emissivity = Absorptivity

**Q218. Statement 1: Water kept in an open vessel will quickly evaporate on the surface of the moon**

Statement 2: The temperature at the surface of the moon is much higher than boiling point of the water

218(c) Water evaporates quickly because of lack of atmospheric pressure, also temperature of moon is much higher during day time but it is very low at night

**Q219. Statement 1: Specific heat of a body is always greater than its thermal capacity**

Statement 2: Thermal capacity is the required for raising temperature of unit mass of the body through unit degree

219 (d) Specific heat of a body is the amount of heat required to raise the temperature of unit mass of the body through unit degree. When mass of a body is less than unity, then its thermal capacity is less than its specific heat and vice-versa

**Q220. Statement 1: The coefficient of volume expansion has dimension K**

^{(-1)}Statement 2: The coefficient of volume expansion is defined as the change in volume per unit volume per unit change in temperature

220 (a) As r=∆V/V∆t, i.e., unit of coefficient of volume expansion is K

^{(-1)}