# How can I determine whether my basic circuit will work? A battery and two light sources...

## Main Question or Discussion Point

Homework Statement:: How can I determine whether my basic circuit will work? A battery and two light sources.
Homework Equations:: conceptual question, use basic ohms law, current law, voltage law, etc.

This is not a homework question, i am just trying to understand electronics better. I am in my last year of electrical engineering undergraduate courses and I never understood some basic applications. Let me describe a scenario:

I have a 9V battery, two 9 volt bulbs. Can I connect these properly with both light sources connected correctly?

Firstly, is my instinct that I dont have enough information correct? This is how I want to approach this question. I want to know how much POWER i supply to the circuit, then I want to know how much maximum power is allowed to be dissipated by each bulb. Am I going in the right direction? If so then I would calculate the maximum power that my source can provide by multiplying its maximum voltage to its maximum current. I can keep going but I want to know your opinion about my current method. Thank you.

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berkeman
Mentor
You should be able to connect those two 9V bulbs in parallel, fed by the 9V battery. The other considerations are that the battery will discharge twice as fast as with one bulb, of course, and if the battery is near the end of its life, it may have too low of an output voltage and too high of a source resistance to light the bulbs well. Does that help, or am I missing the point of your question?

anorlunda
Mentor
then I want to know how much maximum power is allowed to be dissipated by each bulb.
That is a property of the bulb or LED or whatever. You need to get that data from the manufacturer. Old fashioned incandescent light bulbs had a label like 60W for 60 watts of power printed on the package.

Can I connect these properly with both light sources connected correctly?
I have no idea what this means. In communicating about circuits, a schematic of some sort is the best approach.

You should be able to connect those two 9V bulbs in parallel, fed by the 9V battery. The other considerations are that the battery will discharge twice as fast as with one bulb, of course, and if the battery is near the end of its life, it may have too low of an output voltage and too high of a source resistance to light the bulbs well. Does that help, or am I missing the point of your question?

Thank you. I can connect these two bulbs in parallel because the voltage will be 9 volts across both according to the Kirkoffs voltage law. Am I correct to think that I need to make sure the battery will supply enough current for both bulbs too?

davenn
Gold Member
2019 Award
Am I correct to think that I need to make sure the battery will supply enough current for both bulbs too?

Yes .... so you were asked earlier to tell us the wattage rating of the bulbs
did you find that out ? and what is your 9V battery ?
If it is the standard PP3 type like this .....

and the bulbs/globes are more than about 1/4 watt The battery wont last long
as those batteries can only supply around 300mA

Dave

Yes .... so you were asked earlier to tell us the wattage rating of the bulbs
did you find that out ? and what is your 9V battery ?
If it is the standard PP3 type like this .....

View attachment 255856
and the bulbs/globes are more than about 1/4 watt The battery wont last long
as those batteries can only supply around 300mA

Dave

Sorry Dave, this question was asked to gain a further understanding of the application itself; I had to intention to get an actual answer. Thank you for the insight, I am confident in my erudition on this application now.

davenn
Gold Member
2019 Award
Far out .... if you don't want answers, DONT ask questions !

Am I correct to think that I need to make sure the battery will supply enough current for both bulbs too?
Did you not expect someone to answer it ??

berkeman
Mentor
Sorry Dave, this question was asked to gain a further understanding of the application itself; I had to intention to get an actual answer. Thank you for the insight, I am confident in my erudition on this application now.
Far out .... if you don't want answers, DONT ask questions !
LOL Dave.

I'm just guessing and trying to read between the lines of what the OP posted, and I'm thinking he meant that he was trying to understand the overall concepts of light bulb ratings, etc., and not the details of battery life in an actual application. Of course, I could be wrong, but whatever.

LOL Dave.

I'm just guessing and trying to read between the lines of what the OP posted, and I'm thinking he meant that he was trying to understand the overall concepts of light bulb ratings, etc., and not the details of battery life in an actual application. Of course, I could be wrong, but whatever.
yes, i wanted to learn the concept and not the details. I learn from examples and scenarios. Thank you Dave

davenn
Gold Member
2019 Award
i wanted to learn the concept and not the details.
Well the "devil is in the details"

[Moderator: snark removed.]

Last edited by a moderator:
Well the "devil is in the details"

[Moderator: snark removed.]
Aye, ill keep that in mind.

"I am in my last year of electrical engineering undergraduate courses and I never understood some basic applications. "
I find this extremely difficult to believe. In addition, your other posts seem to have a ring of "troll" about them, rather like asking "which way up does a cat land if it has a piece of buttered-side-up toast strapped to its back?"

anorlunda
Mentor