Copper ions-releasing IUDs are more efficient than non-medicated methods. Why?

Explain why, heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water.

Explain why : (a) a body with large reflectivity is a poor emitter (b) a brass tumbler feels much colder than a wooden tray on a chilly day (c) an optical pyrometer (for measuring high temperatures calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot Iron plece in the open, but gives a correct value for the temperature when the same plece is in the fumace (d) the earth without its atmosphere would be inhospitably cold (e) heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

Why water is more elastic than air ?