A fan with copper winding in its motor consumes less power as compared to an otherwise similar fan having aluminium winding.Explain.

(i) A poor emitter has a large reflectivity . Explain why. (ii) A copper tumbler feels much colder than a wooden block on a cold day. Explain why. (iii) The earth would become so cold that life is not possible on it in the absence of the atmosphere. Explain why? (iv) Why clear nights are cooler than cloudy nights? Why does a piece of red glass when heated and taken out glow with green light? (vi) Why does the earth not become as hot as the sun although it has been receiving heat from the sun for ages? (vii) Animals curl into a ball when they are very cool. Why? (viii) Heat is generated continuously in an electric heater but its temperature becomes constant after some time. Explain why? (ix) A piece of paper wrapped tightly on a wooden rod is observed to get charred quickly when held over a flame as compared to a similar piece of paper when wrapped on a brass rod. Explain why? (x) Liquid in a metallic pot boils quickly whose base is made black and rough than in a pot whose base is highly polished . Why?

A wet porous subtance in the open air loses its moisture at a rate proportional to the moisture content. If a sheet hung in the wind loses half its moisture during the first hour, then the time when it would have lost 99.9% of its moisture is (wether conditions remaining same)

A power transmission line feeds input power at 2300 V to a stepdown transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230 V?

A power transmission line feeds input power at 3300V to a step down transformer with its primary windings having 2000 turns. What should be the number of turns in the secondary in order to get output power at 330V.

Two wires of equal length, one of aluminium and the other of copper have the same resistance. Which of the two wires is lighter ? Hence explain why aluminium wires are preferred for overhead power cables. (rho_(Al) = 2.63 xx 10^(-8) Omega m , rho_(Cu) = 1.72 xx 10^(-8) Omega m, Relative density of Al = 2.7 , of Cu = 8.9 )

Two wires of equal length, one of aluminium an the other of copper have the same resistance. Which of the two wires is lighter ? Hence explain why aluminium wires are preferred for overhead power cables. (rho _(AI) =2.63 xx 10 ^(-8) Omega m, rho _(Cu) =1. 72 xx 10 ^(-8) Omega m. Relative density of Al =2. 7 of Cu =8.9. )

A power transmission line feeds input power a 3300 V to a step down transformer with it primary windings having 2000 turns. Wha should be the number of turns in th secondary in order to get output power a 330 V ?