# Parallel and Series circuits and current

1. Apr 26, 2015

### motyapa

1. The problem statement, all variables and given/known data

2 different questions that I'm using to test my understanding of the physics concepts rather than the math:

1)
How does the brightness of bulb A compare to that of bulb C?

After D is added how does the brightness of bulb A change?
Does the brightness of B change?
Does the current through the battery change?

2)

What is the current through 1, 2, 3?
What is the current through C, D, E?

2. Relevant equations

Less math more conceptual, so no equations to use (plus we havent learned any equations for circuits yet)

3. The attempt at a solution

so for 1a I said that bulb A is brighter than bulb B/C because B & C are in parallel with each other, it increases the current through bulb A.

1b I said bulb A becomes brighter, because the addition of bulb D increases the current throughout the whole circuit. Bulb B does not change brightness because the current through its portion does not change, and the current through the battery increases since the overall current through the whole circuit increased.

For 2 I said the current through 1 is 60, equal to the bulb. For 2 I said it's 30, since 30 goes through B, which means 30 will go through C, so 30 reaches the battery equal to the bulb. For 3 I said it's 120, because D and E both have 60 mA since they're in parallel, so the total is 120.

Does my reasoning of these concepts seem good or am I off on something?

2. Apr 26, 2015

### haruspex

All good, except how the addition of D affects B in 1. Think about the voltage drop across A.

3. Apr 26, 2015

### motyapa

I used this website to try and help me to reach my answer: http://epb.apogee.net/foe/fcspp.asp [Broken]

it seems like adding more in parallel shouldnt change how bright the other parallel ones are? I'm confused why B should change.

Last edited by a moderator: May 7, 2017
4. Apr 26, 2015

### haruspex

You are assuming the voltage across B does not change.

Last edited by a moderator: May 7, 2017