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# if frequency of electric is 50 Hz, how many time flash lamps

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#### ziyas

##### Member level 1
if frequency of electric is 50 Hz, how many time flash lamps? 50 or 100

Incandescent lamps don't flash or flicker significantly.

Flurescent lamps with an electromagnetic ballast flicker at 100Hz or 120Hz depending on the local mains frequency.

Flurescent lamps with electronic ballasts flicker at much higher frequencys.

100 times on 50mHz AC

hi
sin(2*pi*50*t)=0
2*pi*50*t=n*pi
t=n*pi/(2*pi*50)=n/100

Re: if frequency of electric is 50 Hz, how many time flash l

50 times cause .... if yr frequency is 1 hz.... then half time it will be on and half time it will be off... so two stages one on and one off .... so only on stage will count as a flashing... so basically u can see only one flash... but in 50 hz... 50 flashes in one sec and 100 time flickers in one sec. [ on1 off1 on2 off2 .... on50 off50]

Re: if frequency of electric is 50 Hz, how many time flash l

100 times on 50mHz AC

You mean "100 times per second at 50HZ AC"

sin(2*pi*50*t)=0

No, it varies with t. The average is zero.

if yr frequency is 1 hz.... then half time it will be on and half time it will be off.

Wrong.
The luminosity varys with applied voltage, it does not suddenly go from light to dark.
This is an incorrect conclusion, at 2Hz it will still be, to some aproximation,
light half the time and dark half the time. That depends on the duty cycle not the frequency.

so two stages one on and one off ... so basically u can see only one flash
Wrong. Look at this diagram.

Re: if frequency of electric is 50 Hz, how many time flash l

hi
i think 50 is the right answer

regards

Here's a story about tungsten lamp flicker causing grief during a film shoot. Mains was 60 Hz, so the flicker was 120 Hz:

When talking about flash we should define what is the flash ? Are we talking about light intensity cycle when it goes from ON to complete dark OFF (human perceived dark)? Or we about less than 100% AM modulation of light?
Usual lamps do not switch off light radiation for a time 1/50 sec, they are inertial. AC modulates the light - when experimenting with photodiode just direct AC lamp ligh and modulated photodetector output is on the scope display wiill show that well. That is why remote control signals are usually modulated with much higher than 50 Hz frequency .

For me - there is no flash at all ))

hi

it is equal to: (2*50)+1=101 times

regards

Thanks for that link echo47, Obviously small incandescent lamps can produce a stroboscope effect in some circumstances.

I vagly recall seeing effects from small torch bulbs run from low voltage AC.
it is equal to: (2*50)+1=101 times

You can choose a paticular 1 second interval during which you have 101 peaks of light intensity, you can also have a 1 second time window during which you have 100 peaks of light, it depnds on the phase of the AC relative to your sampling window.

The flash rate is still 100Hz.

Re: if frequency of electric is 50 Hz, how many time flash l

becouse of the percistance of the wire in the lamp there is no flashes per second

its all theory ....

Re: if frequency of electric is 50 Hz, how many time flash l

there are flashes, but your eye is not able to see it. It reacts to slowly to the flashes and you experience it as a constant source.

It is 100, because in each sine cycle there are two maximums which represent 2 flashes.

The answer of 101 really made me think! the only explanation I can have is that it is the number of "offs" instead of "ons"

See ya

Sal

hi again,

first we must define flash!

FLASH: crossing from OFF state to ON state.

therefore >> the answer is 101. (it is independent from the windowing)

regards.

For visiable artifacts a flash is the entire on state phase of a signal. In the case of an AC signal this is From 0 volts to positive peek, back down to 0 volts, and from 0 volts to negative peek and back up to 0 volts. So there are two 'flashes' per AC phase of an incadescent bulb. In the case of a 50hz lines this is 100hz and 60hz line it's 120hz.
I don't know about any of you but I can spot a car with LED brake/turn lamps from 50 feet away by noticing that they don't dim/brighten like normal incadescents do. Since mains AC is at least 50hz this dimming isn't noticeable to the human eye. Human eye can see flicker at 50-60hz easily when it's abrupt on/off but not when it's only the slight dimming effect of an AC bulb, so the human eye is never aware of any kind of flicker, it's just too small. It does however exist, as someone mentioned using a photo diode. You can also use a Cadmium sulfide cell as a resistor in a simple audio oscilator and amplify it a lot and you'll be able to hear the line hum from a light bulb.

Funny you mentioned LED brake lights. I'm seeing the same instant on/off effect in red/yellow/green roadway traffic signals. Our city maintenance crew is gradually replacing the old incadescent bulbs with LED clusters.

Re: if frequency of electric is 50 Hz, how many time flash l

No matter how many times they flash, if you blink your eyes quiclky enough and sync, you'll never see the flashing :-D

Re: if frequency of electric is 50 Hz, how many time flash l

In AC there are 2 peaks ,the +ve maximum and the -ve maximum , and the lamp will be off only in the region of 0 crossing where the voltage is not sufficient to glow the filament . for 1Hz there will be two on state and two off sate . so for 50Hz the flashing rate will be 100 . since the on time will be more than off period eye cannot see the flickering.

in a periode T the wave will cross the zero 2 times we have 50 periode per 1 second so it will flash 2x50 = 100 times per 1 second

regards

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