Question

Two electric bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to electric mains of 220 V. Find the current drawn by the bulbs from the mains.

Answer 1

Firstly calculating the resistance of the electric bulbs,

P=`"V"^2/"R"`

⇒ `"R"="V"^2/"P"`

⇒ `"R"_1 =220^2/100 =484 Ω`

⇒ `"R"_2=220^2/60=2420/3 Ω`

`"R"_"eq" = ("R"_1"R"_2)/("R"_1+"R"_2)=(484xx(2420//3))/(484+(2420//3))=302.5Ω`

Total current drawn by the bulbs from the mains supply,
`"I"=220/302.5=0.73 "A"`