The discussion revolves around calculating the power consumption of a light bulb connected to a 120-V outlet that draws 0.5 A of current. The subject area includes electrical power calculations, particularly in the context of alternating current (AC) versus direct current (DC).
The discussion is active, with participants providing insights on the implications of using RMS values and the conditions under which the formula applies. There is acknowledgment of the assumptions regarding phase shifts in resistive loads like light bulbs.
Some participants note the lack of explicit mention of alternating current in the original question, while others highlight the common use of RMS values in household electrical systems.
Yes. I think you meant P = IVAprilshowers said:Question:
How much power does a light bulb connected to a 120-V outlet use if it draws .5A of current?
My answer is:
P=1.V
=.5 x 120
=60Watts
Does that look correct?
I can't say I know of many 120VDC outlets around...dextercioby said:It doesn't say about alternating current.
Daniel.
There is a 0 phase shift between voltage and the current passing through a light bulb, which is resistance with virtually 0 reactance.NewScientist said:If you are dealing with alternating currents the equation becomes:
P = I.V.cos(h)
Where h is the phase shift between the graph of voltage and of current.
-NewScientist
If the light bulb, which is a pure resistor, is drawing .5 amps (RMS) with 120 volts (RMS) across it, it is consuming 60 watts of power (RMS). There is always a 0 phase shift if the load, like a light bulb, is a pure resistor.NewScientist said:Exactly, but there is not always 0 phase shift, that is why in that case cos (h)=1 as h = 0. Therefore the result can be simplified to IV.
In some cases cos(h) is not 1 as the phase shift is not 0 and so this ter mis useful.
-NewScientist