An Intimidating Experience

[Nowhere-Man]

Suggest that you read about and understand Ohm's lawa and Kirchoff's laws.

http://www.bbc.co.uk/schools/gcsebitesiz...rev3.shtml
http://www.electronics-tutorials.ws/dcci...dcp_4.html

Kirchoff's most widely known theory is the junction current, whereby current coming into a circuit or crossroads has to part the circuit at equal value.

Sorry, your explanation doesn't quite make sense, even as English**, let alone engineering. I thnk you're trying to explain KCL, which simply states that the sum of currents flowing into a junction is always zero. It can also be stated as the sum of currents entering a junction must be equal to the sum of currents leaving that junction.

If you apply KCL, KVL and ohm's law to any linear circuit (and many non-linear ones) your should understand what's happening. A certain caution is needed if non-linear devices are included as ohm's law can only be applied at the particular voltage across the non-linear device and current though it. A filament lamp is not linear (its resistance rises with temperature) but ohms law can still be usefully applied. That same non linearity also makes it useful in a lamp limiter. At low currents the resistance is low, so the radio etc will operate more or less normally. If the radio is faulty and tries to take a high current the resistance of the lamp will rise and thus protect the radio.

Once you've really understood KCL, KVL and ohms law you tend to use them instinctively, without even reailising you're using them. That comes with experience.

**With apologies if English isn't your first language.

I think I was trying to say where you have a milliamp value which enters a circuit junction, say, 0.2 Amp plus 0.5 Amp coming into the junction, the rule is you can't have a higher value leaving the same junction on the way out. It's ages ago since I needed to use it, but put simply I'm aware current doesn't change in series resistances which is why the current stays the same in a series heater circuit but voltage can drop along a chain. For example, in an ACDC set a large resistor is used to drop voltage for HT and also for the heater chain voltage. This needs to be worked out in case where a line dropper is broken and the resistances may need to be worked out but, again, it was ages ago since I needed to do this.

It got more complex when capacitors were used but I totally forgot the maths to that.

I just simplify it and think of voltage dividers.

In this specific case, if a 100 watt resistor was fixed value and not a lamp, I'd look at the first resistance as being a bit above 500 Ohm and then the set itself is going to have a resistance too. Not quite sure what that is by memory although I think typical current is usually 170 milliamps So, the voltage is going to be divided between 2 resistances.

Anyway if it's a 100 watt lamp and the lamp burns bright then current must be rising in the set while voltage drops. Presumably if the lamp is dull then there ought not to be excessive current draw in the set.

I have heard of lamps being used as resistors but mainly in cases to drop voltage in a line chord. Or the term "barreter" rings a vague bell.