Does the filament of a bulb have constant resistance, constant voltage or constant current?
I would think it's constant current. But can someone logically explain why? I can't understand it much.
resistance changes with temperature, and temperature changes dramatically as the bulb heats up.
Current changes dramatically from turn on to heated condition.
Voltage remains constant from the supply, usually.
What about for an LED? Wouldn't that at least have constant current? I'm asking this because for an assignment where we had the previously stated question I put constant current which was marked correct. But with your help and research I've realized it should actually be constant voltage. So maybe I misinterpreted the question, if it was meant for LED filament then would it have constant current?
The filament of a bulb, commonly made of tungsten, has a property of having a constant resistance. This means that its resistance remains the same regardless of the voltage or current applied to it.
To understand why the filament has a constant resistance, we need to explore the relationship between voltage, current, and resistance. Ohm's law states that the current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance. Mathematically, Ohm's law can be written as:
V = I * R
where V is the voltage applied across the conductor, I is the current flowing through the conductor, and R is the resistance of the conductor.
In the case of a filament bulb, the voltage is typically constant (e.g., 120V for household bulbs), which means the current flowing through the filament depends on its resistance. Since the resistance of the filament remains the same, the current passing through it remains constant.
To ensure this constant resistance, the filament is designed and manufactured in a specific way. The filament is usually made of a long, thin wire with a high melting point, like tungsten. This wire is coiled to increase its total length, thereby increasing its resistance. By carefully choosing the material and dimensions of the filament, manufacturers can ensure that the resistance remains relatively constant over a range of operating conditions.
In summary, the filament of a bulb has constant resistance, and as a consequence, when a constant voltage is applied to it, it results in a relatively constant current flowing through the filament.