(1) An electric iron is rated at 750W,230V.Calculate the electrical energy consumed by the iron in 16 hours.
(2) Two bulbs are rated 60W,220V and 60W,110V respectively. calaulate the ratio of their resistances.
(3) An electric bulb is rated 250 W,230V.Calculate -
(i) the energy consumed in one hour,
(ii) the time in which the bulb will consume 1.0kWh energy when connected to 230V mains .

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Answers

2015-10-11T21:48:23+05:30
1 power p= 750w
  time t=16 hrs
electrical energy E=  p* t
=750*16 watt-hr
=12000 watt-hr
=12kw-hr

2. p=v^2/r
for bulb 1 60=(220*220)/r
r= 806.667 ohm

for bulb 2 60=(110*110)/r
r=201.667 ohm

so bulb 1 to bulb 2 ratio is = 4:1

3.

E=p*t
=250 watt*1 hr
=250 watt-hr
t=E/p=1000watt-hr/250 watt= 4 hrs
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