If all you have is a 120-V line, would it be possible to light several 6-V lamps without burning them out? How?

1 Answer
Dwight
Feb 18, 2017

This question is about series and parallel connections. Here, you must connect 20 of the bulbs in series to make it work.

Explanation:

When we connect a number of devices in series across a voltage source, the voltage is divided among those devices, in a proportion that is based on the resistance of each device.

As an example, suppose we have two resistances, #1Omega# and #2Omega# that we connect in series across a 12 volt power supply. Since the total resistance of the two in series is #3Omega#, the current that will run is

#I=V/R=12/3 = 4 A#

When a #4 A# current passes through a #1Omega# resistor, the voltage drop is

#V=I*R=(4 A)*(1 Omega) = 4 V#

The same current then passes through the #2Omega# resistor, and the voltage drop is #8 V#.

In this way, the two series resistors have divided the source voltage, with the larger resistance causing the greatest voltage drop.

Now, if you must use a #120 V# source, but have only #6 V# across each bulb, it will be necessary to divide the 120 volts into twenty #6V# drops, which is exactly what happens if you connect twenty identical resistors (the bulbs) in series.

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