Ravi asked in Science & MathematicsPhysics · 6 years ago

why my light bulb is not quickly turn on and off because of a.c line to my house?

i know its stupid question but.. you know what i mean..:)

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  • 6 years ago
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    Although oldprof and morningstar make good points about oscullation, neither is the case for lightbulbs. The key is heat, as morningstar points out in his second paragraph.

    You need to ask yourself why light bulbs turn on in the first place. The current going through them causes heat to generate in the wire. This heat causes the filament to glow. It is a heat glow.

    When the current changes direction, the current still passes through the wire and the friction still exists... the bulb continues to glow hot, despite the change in direction of the current passing through it.

    The bulb does not have a chance at 50-60 Hz to ever cool down and turn off in the first place, not even for a quick blink.

    If you have ever noticed that slight glow for moments after turning the switch off you understand my point.

  • 6 years ago

    I do I do.

    You have alternating current (AC) into the house. If it's alternating and feeds your lights, why don't the lights blink on when the current is ON and blink off when the current alternative to off.

    The reason is two fold. First the alternating, the oscillation, is not between on and off; it's between one direction and the opposite direction. That is, the current is always there but it moves back and forth within the wires.

    Second, at 50 or 60 cps (typical cycle rates for residences), our eyes are unable to see that oscillation in current direction. In fact must people are unable to discern oscillations above 12 to 15 cps (some will see flicker...thus the term "flicks" for old time movies).

    And there you are. Your light bulb does not flicker because there is always current going one way or the other, and because whatever oscillations there might be are too fast to actually see them.

  • 6 years ago

    If it did, you would not be able to detect it, because it happens 60 times a second. Our eyes have a property called persistence of vision; any image we see lasts a fraction of a second even if the light we see ceases. Note that movies flash still images at rates such as 24 times per second, but we don't notice a difference from real motion.

    In old-style incandescent lights, the current heats a filament which then glows white-hot. The heat does not dissipate as fast as the current. It continues to glow even during the two times per cycle when the current drops to zero.

    I'm not sure about fluorescent lights. They employ a lot of circuitry that alters the flow of current from the original source.

  • 3 years ago

    good question. People have already explained about the human eye and filament bulbs, but they have not said that fluorescent bulbs DO flicker at the mains frequency. in the past, this has cause accidents in engineering workshops, where a machine was rotating at mains frequency, so every time the light came on, a moving part was in the same place, so it looked like the machine was not turning. People would try to adjust the machine and suffer an injury. How they corrected this was to install a filament lamp right over each machine to give constant light.

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