# Switch lamp problem [closed]

I have the answer to the following problem, but I am not sure how they got it. Please explain:

Four identical incandescent light bulbs L1, L2, L3, L4, and a battery are connected as shown on the diagram on the right. The three switches S1, S2, S3 are open. How will the brightness of the four lamps change compared to the original state if the specified switches are closed (all other switches are open)?

Example: S1 closed.
Expected Answer: L1 - off, L2 - same, L3 - brighter, L4 - brighter.

(A) S2 closed;
(B) S3 closed;
(C) S1 and S2 closed;
(D) S2 and S3 closed.

A) Answer: L1 - brighter, L2 - same, L3 - off, L4 - off
B) Answer: L1 - off, L2 - same, L3 - off, L4 - brighter
C) Answer: all lamps off (short circuit)
D) Answer: L1 - brighter, L2 - same, L3 - brighter

Thank you so much!

• I recommend grounding the lower-left corner wire and then redrawing the schematic so that it is not so confusing. As you work to unwind it, I believel things will become much much clearer to you and you won't even need us to help out. (In fact, it's what I'd have to do myself before bothering to consider an answer.) – jonk Apr 4 at 21:44
• We don't hand out answers to homework here without seeing the OP demonstrate that they have done a substantial amount of work. Show us all of your work and then ask a specific question. I know you think you have "the answer" but in many cases the "how" is the real answer you are expected to provide. – Elliot Alderson Apr 4 at 21:45
• GoldenRetriever - Hi, I see that you removed the "homework" tag that I added. I have reinstated that. This is a homework-type question, and it will be treated that way here. In other words, please edit the question and add your own attempt at explaining the behaviours for scenarios (A) - (D). Show where you get stuck in your analysis. Then readers can explain more. Failure to add your own solution attempt is likely to cause the question to be closed (actually, put on-hold) quickly. Thank you. – SamGibson Apr 4 at 23:11
• I have the answer to the following problem ... there are four solutions, not one ... which one do you not understand – jsotola Apr 5 at 2:07

Here's how I'd redraw your schematic:

simulate this circuit – Schematic created using CircuitLab

I think you should be quite able to work out the details for yourself from the above. It's now "easy to read." You really should exercise your skills in redrawing schematics. It will take you very, very far in situations like this one.

For example, it is now very easy to see that closing both $$\SW_1\$$ and $$\SW_2\$$ will short out the power supply. You can also easily see that no switches affect $$\LAMP_2\$$ unless they short out the power supply.

See below: