CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@selvaece2004 • 30 Oct, 2009
1) Two lamps of 200W,200V and 100W,220V are connected in series across 220V supply.The ratio of current through theem will be
i) 1:2 ii)1:1 iii)2:1 iv)1:4

2)Two heaters,rated at 1000W,250V each are connected in series across a 250V,50Hz ac mains.Total power drawn from the supply would be
i) 1000W ii)500W iii)250W iv)2000W

3)A 200W,230V lamp is connected across 115V supply.The lamp will draw power
i)slightly more than 50w ii) less than 50W iii)50W iv)none of these

4)In two parallel conducting plates,each of area a and having charge density p,the force of attraction between them will be
i) (p^2*A^3)/(2*effsalan) ii)(e^2*A)/(2*effsalan) iii)p^2/(2*effsalan)
@reachrkata • 31 Oct, 2009 1) 1:1
2) 2000W
3) 50W
4) (1/4*Pi*Epsilon)(p^2*a^2/d^2) - None of the choices.

- Karthik
@selvaece2004 • 01 Nov, 2009 But they gave answer for
1) 1:2
2) 500W
3) slightly more 50W
4) i
@reachrkata • 01 Nov, 2009
1) I totally disagree with them. When you connect two loads in series, the current through them is always the same. WHATEVER YOU DO !!!😒

2) Correct. I stand corrected, it is 500W. Thats because, the both are rated 250V,1000W. So when you apply 250V to both, they get half the voltage, which means they give only 1/4 the power. In total it is 500W.

3) Same logic as above. If you give half the voltage, you will get 1/4 the power.

4) Dont know how? Can you get the explanation too.

- Karthik

@BigOhm • 02 Nov, 2009 (1) is 1:1 as reachrkata clearly stated.
(2) has no correct answer. Heaters are non-Ohmic.
(3)has no correct answer. Lamps are also non-Ohmic
(4) has no correct answer listed. The question is very poorly stated.
@reachrkata • 06 Nov, 2009 Hey Big Ohm,

All electrical devices are Ohmic in a way. The heating element in the heater is Ohmic and so is a lamp.

@BigOhm • 06 Nov, 2009
Hey Big Ohm,

All electrical devices are Ohmic in a way. The heating element in the heater is Ohmic and so is a lamp.

Only if you can figure out how to run them at constant temperature (kinda defeats the purpose of a space heater, though 😔).
@reachrkata • 11 Nov, 2009 Of course, based on the temperature the Ohmic value would vary.
But the device remains Ohmic nevertheless !😉

@BigOhm • 11 Nov, 2009 The game is not worth the candle. You may indeed call such an effect Ohmic when corrected for temperature. I may equally well call it non-Ohmic. There is no bright line separating the cases. Nonetheless, whatever we call the effect, the resistance of a hot lamp cannot be measured cold.
@risahe • 30 Nov, 2009 I think this is not a very diffcult problem, you should think is by yourself.
@omm87 • 27 Oct, 2015 there is a simple formulation given by power to calculate the consumption....
and solve your requirement

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