(a) List the factors onwhich the resistanceof a conductorin the shape of the wire depend. (b) Why aremetals good conductors of electricity whereasglass is a bad conductorof electricity ? Give reason . (c ) Why are alloys commonly used in eletricalheating devices ? Give reason.

(a) List the factors onwhich the resistanceof a conductorin the shape

1.	(a) List the factors onwhich the resistanceof a conductorin the shape of the wire depend. (b) Why aremetals good conductors of electricity whereasglass is a bad conductorof electricity ? Give reason . (c ) Why are alloys commonly used in eletricalheating devices ? Give reason.
Answer» Solution :(a) Factorsonwhich theresistance of a conductor in the SHAPEOF a wire depends. (i) Theresistanceof a straightconductoris directlyproportionalto its length. `R prop l` (ii) The resistanceof a straightconductoris inversely proportionalto its area ofcross-section . `R prop l/A` From (i) and (ii) `R prop l/A` `:. R = rho'l/A`, ...[`rho` = constantcalledresistivity] (iii) the resistanceof a conductor also dependsuponthe temperature of the conductorand nature of materialused. (b)Metalshave free electronswhich helpsthem in the conductionof electricitywhereasglass hasno free electronsthereforeit is aninsulator. The resistivityof GLASSIS very HIGH `(=10^(10 ) "to" 10^(14) Omega m)` thereforeit is a poorconductorof electricitywhearesthe resistivity of metalsis lower,thereforemetalsare food conductors of electricity. (c ) Alloys arecommonly used in elctricalheatingdevices because - the resistivitiesof alloys are muchhigherthan those of the puremetals(fromwhich theyare made), an alloy does notundergo oxidation(or burn) easilyeven athigh temperature . Thusheatingelementsof electricalheatingappliances such aselectric iron,toaster, etc.are madeof an alloyrather thana pure metal .