A globe from a torch and a refrigerator bulb are connected in series across a power supply. Predict what would happen?
Let's start by calculating the operating resistance of the two bulbs.

Given V = IxR, the torch bulb will have a resistance of about 12 ohms.

Given P = V^2/R, the refrigerator will have a resistance of about 5760 ohms.

With me so far? Now let's look at the proposed circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

From this we can calculate the voltage across the torch bulb, and it is $$V=240\frac{12}{12+5760}=0.499 $$

So our 6 volt bulb will have about 1/2 volt across it, and will barely light up.

This is not the most accurate analysis, since (as you probably don't know) light bulbs do not have a constant resistance. Typically, when cold a bulb filament resistance will be on the order of 10 times less than when hot. In this case, that works to make the bulb even dimmer. A variation of 10:1 won't make much difference in the bulb current, since that is controlled by the 5760 ohms of the refrigerator bulb. But if the torch bulb filament resistance is 1.2 ohms rather than 12, the voltage across the bulb will only be about 0.05 volts, and the the bulb will be really, really dim. Note that this very dim condition is consistent with the low filament resistance derived by assuming the filament is cold, so it's an indication that the assumption was correct.