Question

2 bulbs of 500w and 200w are manufactured to operate on 220v line.What will be the ratio of heat produced in 500w and 200w bulb , when they are joined a)in parallel b)in series

Answer 1

the resistances are 96.8 ohm and 242 ohm
a) in parallel
potential difference is same
so the ratio is 242/96.2
b) in series
current is same
so it is 96.2/242

Answer 2

heat produced =$i^{2} rt$=$(v^{2} /r)t$
calculate resistances using power=v$v^{2}/r$
a)in parallel combination v is same
    heat ratio can be calculated as$h_{1} : h_{2}$=$r_{2} :r _{1}$

b)similarly in series current is same
$[tex] h_{1} : h_{2}$[/tex]=$v _{1} ^{2}* r_{2} :v _{2} ^{2}* r_{1}$