total power dissipation

[filbo]

Hello and all is well mvs sarma
I stated that sallman92 is the examiner metaphorically, only in that he posed the query to the forum.
regards Phil

 

[RCinFLA]

As soon as you make assumptions outside the stated info the problem becomes unsolvable.

There is no fixed profile of wattage vs. voltage reduction for incandescent bulbs (I am reading the schematic symbol as meaning 'incandescent'). Different wattage rating bulbs have different profiles of net watts consumed versus voltage reduction applied. It is related to how hot the filament is run at rated voltage. Long life incandescents run a cooler filament temp at rated voltage to make them last longer (at lower lumens per watt penalty). Quartz halogen bulbs run very hot filament at rated voltage to achieve higher lumens per watts.

Somewhat irrelavant, but suspeciously coincidential, is the bottom two parallel bulbs wattage summation equals the wattage of the top bulb in series. It makes the circuit do-able with standard off-the-shelf bulbs. (well, maybe not off the shelf in Europe). It is not a good way to actually run bulbs as the lower wattage bulbs will likely get a startup, momentary, overvoltage surge that will reduce their lifespan because the top higher wattage bulb will take longer for its filament to come to operating temp where its effective resistance increases.

 

[RCinFLA]

NO one, ever, connects 240V loads in series.

Bah, Humbug,

Obviously never installs Christmas tree lights.

 

[KeepItSimpleStupid]

What they may be trying to do is to make you think. Having two parameters such as P and I, you can find V. Set up the equations and everything.
However, why bother. They asked for total P and that you can do by inspection.

 

[mvs sarma]

Bah, Humbug,

Obviously never installs Christmas tree lights.

when any one installs series lights for decoration, they use number of low voltage lamps, to make up to the line voltage, there after some such chains can of course be paralleled. Yes. we don't use 230V bulbs in series to make chain of lamps to be powered by 230V.

@K I S S ,
we all think but perhaps not the O P

 

[Mr RB]

What they may be trying to do is to make you think. Having two parameters such as P and I, you can find V.
...

Well that's the problem. You don't have P, you have 3 component values.

The examiner needs to be sent home with a score; "4/10, please try harder".

 

[JMW]

Total power is as stated, 120 Watts. Makes no difference whether in series, parallel, any combination or the voltage. What is interesting is the current flow arrows in an AC circuit.