Figure P27.3 shows the interior of a three-way incandescent lightbulb, which provides three levels of light intensity. The socket of the lamp is equipped with a four-position switch for selecting different light intensities, with the positions described as follows: (1) off (switches S1 and S2 both open), (2) switch S1 closed, (3) switch S2 closed, and (4) switches S1 and S2 both closed.
The lightbulb contains two filaments. When the lamp is connected to a 120-V source, one filament receives 100 W of power and the other receives 75 W. What is the total power input of the light bulb when
(a) only switch S1 is closed
(b) only switch S2 is closed
(c) both switches are closed
(d) What if? Suppose the 75-W filament breaks and no longer is able to carry a current. How many switch positions will result in the light leaving the bulb and what will be the power input to the bulb in those positions?
