# Series question. eh?

Discussion in 'General Electronics Chat' started by Lightfire, May 14, 2011.

1. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
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Hello,

I am watching a video about a series and parallel connection and the guy asked which bulb is the nearest to the negative terminal of the battery, as well as which bulb is the brightest. Eh, I see that the bulb which is nearest to negative terminal of the battery is the brightest one.

Eh?

What's the matter about the nearest bulb to negative terminal of the battery?

In series, all bulbs' brightness should be equally. Eh, isn't it?

Thanks...

Apr 5, 2008
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3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
If the bulbs are identical in voltage and power rating then they would notionally glow with the same brightness. What would happen if you placed a 12V 1W globe in series with a 12V 20W globe and connected them to a 12V source?

Oct 5, 2010
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5. ### Adjuster Late Member

Dec 26, 2010
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The bulbs in a series circuit should have similar brightness if of the same ratings. This video looks as if it has been retouched in some way: someone left this comment on the Youtube article, and I think that they got it about right - :

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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If the guy is saying that the globe nearest the negative terminal is always the brightest then its plainly rubbish - but was that what he was saying?

A conclusive test would have been to swap the globes rather than just take one out & put it back.

Because the globe resistances are highly non-linear, even "identical" globes may quite probably show different resistances at the same current - most likely due to variability in manufacturing tolerances. The one with the higher resistance will glow more brightly - the difference may or may not be observable to the naked eye.

7. ### GetDeviceInfo AAC Fanatic!

Jun 7, 2009
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the fact that you question this is good. Being able to weed out the trash is important to one's progress.

What's with the 'eh?

Dec 26, 2010
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9. ### Wendy Moderator

Mar 24, 2008
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I'm wondering if it is some sort of attempt to weed out the students who did the experiment themselves vs. the lazy goofs who just want to use the video?

10. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
21
Adjuster, eh?
Eh?

Um, I have tried that experiment long time ago (the parallel) when I was about 7 years old until now (because i want to see something on it that meets my standards )...

Um, the only difference is I used 2 AA batteries and 2 2.5V flashlight bulbs.

But the effect, just the same!!!... If I pull one bulb, the another is getting brigther. If I put one more, the other is getting dimmer... Eh? Since 7 years old until now can't make it stable even though I have mastered D) it.

11. ### Adjuster Late Member

Dec 26, 2010
2,147
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The change of brightness of the other bulbs in a parallel circuit when a bulb is connected or disconnected is an interesting effect.

It is due to parasitic resistance in the circuit. There may be a very small effect due to wiring resistance, but mostly it is due to internal resistance in the battery. This internal resistance results in the battery voltage reducing as more current is drawn from it, so when a bulb is connected to a battery its voltage gets less.

If another bulb is added in parallel with the first one, the battery voltage will fall lower and the first bulb will get dimmer. If a bulb is then disconnected the current will reduce and so the battery voltage will rise again, so the remaining bulb will get brighter. http://en.wikibooks.org/wiki/A-level_Physics_(Advancing_Physics)/Internal_Resistance

12. ### KJ6EAD Senior Member

Apr 30, 2011
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The guy in the video was speaking sooooooo slowly that I couldn't stand to watch.

13. ### SgtWookie Expert

Jul 17, 2007
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I suffered through some of the video. The two bulbs in series appearing a different brightness was kind of interesting; the bulb on the left had a brighter reflection from the table, but appeared more dim than the bulb on the right. I can only suggest that perhaps the video camera was saturated by the brightness of the left bulb.

There can be small variations of brightness in bulbs from lot to lot or manufacturers; even of the same rating.