Question

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

Answer 1

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.