Really basic what happens when the switch closed question

[scilearner]

Hello guys,

 

I got a small question. It says circuit consists of three identical lamps connected to a battery with a switch as shown in the diagram. When the switch is closed what happens.

 

I did this really quick on paint.

 

 

It says that lamps C turns off because no current flows through it. But I don't get it. Shouldn't the current divide and each section get some current. Why is C getting no current when the switch is closed. Any help would be appreciated. Thanks

[ydoaPs]

What is the resistance of bulb C? What is the resistance of the wire with the switch in it?

[scilearner]

What is the resistance of bulb C? What is the resistance of the wire with the switch in it?

 

Thank you for replying. This question is not about numbers and I think the resistance should be same because they are identical lamps. Why is that when te switch is closed that current only flows through A and B. I thought current would divide.

[SH3RL0CK]

Look at it from the voltage standpoint. What is the voltage drop across the switch when it is closed? Will it be a large voltage or a small voltage? Take this voltage across the bulb C and determine the current which will flow through bulb C by Ohms law, I = V/R.

 

This should give you the answer you are looking for.

[Janus]

Thank you for replying. This question is not about numbers and I think the resistance should be same because they are identical lamps. Why is that when te switch is closed that current only flows through A and B. I thought current would divide.

 

Generally such drawings are of ideal circuits. IOW, the wires are considered as have zero resistance. The lamps are considered as loads with some finite resistance. when current divides between two branches, the amount of current that travels through each branch depends on the relative resistances of the branches.

 

If they are equal, equal current travels through each branch.. If the total current is 10A, 5 A travels through each branch. If the resistance in one branch is half that of the other, twice as much current travels though it.

 

When one branch has zero resistance and the other has any resistance, then all of the available current passes through this branch.

 

 

In real life the wire has some small resistance, but it will still be very small compared to the resistance of the lamp. Thus the vast majority of the current will pass through the branch on with the switch, leaving only a very small current to pass through the lamp. This current will be so small that it won't be enough to cause the light to glow.

[scilearner]

Thank you everyone who helped:-). Especially Janus. I think I get it now. The current took the path of least resistance in this circuit. Let's say there was a resistor in the wire with the switch then you would see more current flow to the globe. Am I right!!. Thanks a lot for the help guys. Really appreciate it.

[ydoaPs]

Thank you for replying. This question is not about numbers and I think the resistance should be same because they are identical lamps. Why is that when te switch is closed that current only flows through A and B. I thought current would divide.

 

Sorry. I like to use the Socratic Method to try to get YOU to come up with the answer. I asked you about the resistances because that would let you see that there is a really high resistance for the bulb, and a really low(typically assumed zero for these kinds of problems) resistance for the wire. Would current rather flow through a lot of resistance or none?

[thedarkshade]

What's with the picture?

[iNow]

What exactly about the picture is confusing you, thedarkshade?

[ydoaPs]

LOLLY ROFFLES

 

I guess the OP didn't like the diagram he had before.

[thedarkshade]

What exactly about the picture is confusing you, thedarkshade?

Umm... the point of it!

[iNow]

Umm... the point of it!

 

Gotcha.

 

Very weird. The previous picture was still be shown on my system when you posted that comment. Now, when I launch the thread this time, some strange new picture is there with a little cartoony man at the end of some game.

 

 

EDIT: Aha. He uploaded his image to some photo sharing site, and the filename on his image was "untitled.jpg." He has since uploaded a new image with that same filename (untitled.jpg) and overwritten the previous which had been showing in the OP.

[5614]

EDIT: Aha. He uploaded his image to some photo sharing site, and the filename on his image was "untitled.jpg." He has since uploaded a new image with that same filename (untitled.jpg) and overwritten the previous which had been showing in the OP.

Well that's not a very good image upload site then, is it!? Use Photobucket or Imageshack instead.