How do light bulbs go out?
In: Chemistry
If you mean how does a light bulb blow, it’s when the brightly glowing wire (or ‘filament) inside them breaks.
When you first switch on, the most stress is on the filament, and then as the filament heats up, the stress on it becomes less.
Think of it like a tug o war, at first there’s a huge amount of stress on the rope, but before long, the people participating get tired, and the strain on the rope gets less.
As long as the rope can put up with that initial real hard tug, it’s probably not going to break. The light bulb filament is the same.
As long as it can cope with that initial switch on stress, it’ll likely be fine. This is why when light bulbs blow, they tend to when you first turn them on.
If you want the more advanced reasoning behind it, it’s this:
Light bulb filaments are what’s called a resistive load, so as they warm up, their resistance increases.
If you know about Ohm’s Law, that means for a given voltage, and resistance, a certain amount of current can flow. If you reduce that resistance, more current can flow.
As mentioned above, the filament resistance is lowest when it’s cold (perhaps even as little as 1/10 the resistance of when it’s hot) so at that point it can pass the largest amount of current (10x as much as normal operating conditions). That means there’s more energy going through the filament in those first fractions of a second than when it’s warmed up, and therefore, if it’s going to fail it’s most likely to immediately when turned on and when it does, it’ll be with a -very- bright flash, because there’s an awful lot more energy involved than when the bulb is operating normally.
Assuming it survives that, as it heats up it’s resistance increases and that lets everything settle down to normal operating power (which might be, say, 60 watts).
For a light bulb to go go out it first has to go in. And after it has gone in then it can go out. But before it can come out it should burn out so that you aren’t wasting as much energy. You wont use as much energy because the bulb has in fact burned out by then. So then you can basically can take it out so that it can come out. I hope this response helps.
If you mean “burn out”: the tungsten filament inside a bulb is relatively fragile. When you turn the bulb on and off the filament heats up then cools down. Each heat/cooling cycle will put stresses on the material and over time it will develop weak spots until the material just “breaks” in a spot. Bulbs that turn on/off frequently (like in your entrance hallway, or a bedside reading lamp) will (in general) burn out quicker than ones that are infrequently turned on or are left on for long periods. Of course the bulbs for special purposes like your car headlights or the bulb in your fridge are designed to different robustness standards.
Either by turning it off at a light switch, or by destroying itself by it’s own inductance and breaking the circuit at its own broken element. (the part that glows is a thin metal spring usually tungsten, that glows when current goes across it)
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