When a tungsten filament is giivng off light, does its resistance vary
significantly over a voltage range from 100V to 130V?
On our pro video list we've been having a discussion concerning current
flow through a simple circuit containing a large wattage incandescent
light and different cable lengths.
This is an example of the circuit:
One 1200 Watt tungsten filament (a light bulb) is plugged into a 120
Volt outlet. The cable used is 12/3 copper. If the cable length
increases between the filament and the outlet from 2 feet to 502 feet,
does the current in the circuit increase or decrease?
Others are maintaining that the 1200 Watt bulb remains 1200 Watts no
matter how much resistance is added in series with it to the circuit.
I maintain that the added resistance of the long cable increases the
overall resistance in the circuit lowering the current and the power.
They are saying that the lightbulb's filament lowers its resistance to
compensate for the added resistance in the cable thereby maintaining
the lightbulb at 1200 Watts and the added resistance in the cable adds
additional power draw on the circuit.
Obviously, the longer cable run adds resistance to the circuit, which
along with the filament acts as a voltage divider. The filament is
getting less voltage when in series with the long cable. We're back to
my original question.
But which circuit draws more power, the one with the short cable or the
one with the long cable.
Then there's a related question about resistance dimmers: Do they use
the same amount of power when the lightbulb is dimmed out as when the
lightbulb is at full brightness? I maintain that the bright bulb uses
more power. I think I remember reading tat it takes something ike 5 to
6 times the resistance of the incandescing bulb in series with it to
effectively quinch its glow.
Thanks for your input
16 years ago