Two bulbs are marked 100 W, 220 V and 60 W, 110 V. Calculate the ratio of their resistances.

Explanation

Given :

We know, `P=V^(2)/R`
or `R=V^(2)/P`
`thereforeR_(1)/R_(2)=((V_(1)^(2))/P_(1))/((V_(2)^(2))/P_(2))`
= `(V_(1)^(2)xxP_(2))/(P_(1)xxV_(2)^(2))=((220)^(2)xx60)/(100xx(110)^(2))`
= `12/5`
`R_(1):R_(2)=12:5`