Question

Why most sets of Christmas (holiday) lights say not to connect more than 3 strands together? Explain in terms of resistance, and resistivity.

Answer 1

Resistance is the physical property of a substance because of which it opposes the flow of current i.e. electrons.

whereas the resistivity of the material is the ratio of the product of the resistance and area to the length of the conductor.

The resistance is represented by the symbol R whereas the resistivity is represented by the symbol ρ.

In order to get the bulb to glow, you need a complete circuit. There has to be a path for the current to come out of one end of the battery, go through the filament in the bulb and then return to the battery.

When current passes through the filament, it makes the filament get super hot. Super hot things glow. That's all the bulb does.

But as we connect more than 3 strands together, it increases overall resistance of the circuit.which makes all bulb's light intensity low as well as in causes high load on the power supply and cables which can cause short circuit or burning of cable.

Resistance is the heating effect I²R of the bulbs’ filament resistance, that give visible radiation when the temperature reaches near 2700 K. For example a 60 W bulb takes a current of 40 mA at 240 V, implying a resistance of 6000 ohms.