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[Phys-l] three-way bulb



I'm just finishing my unit on electricity, and have three semi-related
circuit questions dealing with everyday phenomena.

1. A three-way bulb has two filaments, often 50 W and 100 W, which can be
connected separately or together. How is the base of such a bulb made, and
how are the filaments wired in it?

2. I recently read that an electric blanket (with three heat settings)
works in a similar fashion, but that the two resistive elements are
identical. I am trying to visualize the circuit diagram. Are these
elements wired in parallel, with switches on each side of the branch, and
a separate wire connecting the resistors? This would allow each resistor
to operate independently (in parallel) or together (in series).

3. An auto rear window defroster operates on 12 V. I believe the elements
are connected in parallel, and run across much of the back window. Does
anyone know the resistance of a given element, so I can get the total
resistance, current, power, etc? Or is it different for each car?

Thanks in advance for your insights and answers!