Q10.19: NCERT Physics - Part 2 THERMAL PROPERTIES OF MATTER 10.19 Solution: Explain why: (a) a body with large reflectivity is a poor…

**Answer:** (a) Good reflectors are poor absorbers/emitters. (b) Brass has high thermal conductivity. (c) Furnace walls provide reflected radiation. (d) Atmosphere traps heat. (e) Steam has high latent heat. **Step-by-Step Explanation:** (a) By Kirchhoff's law, good absorbers are good emitters and good reflectors are poor absorbers. Hence, a body with large reflectivity is a poor emitter . (b) Brass has much higher thermal conductivity than wood. It conducts heat away from the hand rapidly, making it feel colder . (c) In the open, the red hot iron piece loses heat by radiation to the surroundings. An optical pyrometer calibrated for black body radiation measures only the emitted radiation, which is less than what a black body at the same temperature would emit. In a furnace, the walls reflect radiation back, so the pyrometer measures the correct temperature . (d) The atmosphere (greenhouse gases) traps outgoing infrared radiation from the Earth's surface. Without the atmosphere, this heat would escape to space, making the Earth inhospitably cold . (e) Steam has a large latent heat of vaporization. When steam condenses, it releases this latent heat, providing more heat per gram than hot water which only cools. Hence, steam-based heating is more efficient .