Advertisements
Advertisements
Question
An electric lamp A of 40 W and another electric lamp B of 100 W are connected to 220 V supply. Calculate the ratio of their filament resistances?
Advertisements
Solution
P = `"V.I" = "V.V"/"R"`
`40 = (220)^2/"R"_"A"`
RA = `(220 xx 220)/40`
RA = 110 × 11
P = `"V"^2/"R"`
`100 = (220)^2/"R"_"B"`
`"R"_"B" = (220 xx 220)/100`
RB= 22 × 22
`"R"_"A"/"R"_"B" = (110 xx 11)/(22 xx 22) = 5/2 = 5 : 2`
`"R"_"A"/"R"_"B" = 5: 2`
RELATED QUESTIONS
Name the S.I. unit of electrical energy. How is it related to Wh?
Two resistors A and B of resistance 4 Ω and 6 Ω respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate: (i) the power supplied by the battery, (ii) the power dissipated in each resistor.
Define electric power. An electrical device of resistance R is connected across a source of voltage V and draws a current I. Derive an expression for power in terms of current and resistance.
Point out two main disadvantages of ‘Tree System’.
Two lamps are rated 220V, 50W and the other rated 220V, 100W are connected in series with the mains of 220 V. Explain, why the 50W lamp glows more?
What is ‘Rating’ of an electric appliance?
Three 250 W heaters are connected in parallel to a 100 V supply, Calculate total current taken from the supply.
An electric bulb is rated 240V-60W and is working at 100% efficiency.
(i) Calculate the resistance of bulb.
(ii) (a) Draw the circuit diagram.
(b) What is the rate of conversion of energy in each bulb?
(c) Total power used by the bulbs.
State (i) the S. I. unit, (ii) the household unit, of electrical energy. How are these units related?
