# Simple Curcuit Question (Theory)

• skwz
In summary: The current through bulb B doesn't decrease because it now gets all the current that flows through the circuit.Ok gotcha. So the current through Bulb B increases since it now gets the current that flows through the circuit but this current is decreased for A and D as the equivalent resistance is now increased because all 3 bulbs are in series. So the total current in the circuit decreases, yet this is less than the current that bulb B had going through it before the switch was opened?
skwz

## Homework Statement

http://img153.imageshack.us/img153/8941/physicscircuits1ms3.th.png
a.) The circuit above shows four identical bulbs connected to an ideal battery. Rank the bulbs in order from brightest to dimmest

http://img509.imageshack.us/img509/4655/physics3ya0.th.png
b.) Suppose that switch has been added to the circuit as shown. The switch is initially closed. When the switch is opened, will the current through bulb A increase, decrease, or remain the same?

## Homework Equations

Inet = 0 @ a junction (Kirchhoff's Junction rule)

## The Attempt at a Solution

a.) A = D > B = C
For a, Bulbs A and D have the same current going through both of them since they are in series. Therefore they are equally bright. For the parallel network between bulbs A and D, the current going through the current equals that of the current going through bulbs A and D. The current is split between both bulbs B and C then (identical, so same resistance) and they are half as bright as bulbs A and D

b.) Here is where I'm having trouble. I'm confused about the placement of the switch and the fact does current flow through bulb C still? If the switch were placed before bulb C , then the resistance in the circuit would increase since there is one less bulb in parallel right, meaning less current and a decrease in current through bulb A. But with the placement of the switch after bulb C, I thought, by Kirchhoff's junction rule that the current entering a junction must equal the current leaving or flowing out. Wouldn't bulb B now have more current flowing through it while Bulb A remains unchanged? Any help is appreciated.

Last edited by a moderator:
a) is OK
b) do you mean it matters if the switch is above or below bulb C? In both cases, there can be no current going through bulb C if the switch is open.
Kirchhof's junction rule tells you that I_A_closed = I_B_closed + I_C_closed
and I_A_open = I_B_open
I don't think you can draw any conclusions from that.
(I_A_open is the current through lamp a if the switch is open)

If no current is going through bulb C then does that mean that overall resistance in the circuit is increased since their resistances now add (bulbs A,B, and D are in series now)?

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skwz said:
If no current is going through bulb C then does that mean that overall resistance in the circuit is decreased since their resistances now add (bulbs A,B, and D are in series now)?

I think you mean increased

Woops... yeah meant increased! So if the equivalent resistance increases, then the total current in the circuit decreases and thus current through each bulb decreases?

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skwz said:
Woops... yeah meant increased! So if the equivalent resistance increases, then the total current in the circuit decreases and thus current through each bulb decreases?

The current through B doesn't decrease because it now gets all the current that flows through the circuit.

Ok gotcha. So the current through Bulb B increases since it now gets the current that flows through the circuit but this current is decreased for A and D as the equivalent resistance is now increased because all 3 bulbs are in series. So the total current in the circuit decreases, yet this is more than the current that bulb B had going through it before the switch was opened?

## 1. What is a simple circuit?

A simple circuit is a basic electrical circuit that consists of a power source, a load, and conductors that connect them. The flow of electric current in a simple circuit follows a closed loop path.

## 2. What is the purpose of a simple circuit?

The purpose of a simple circuit is to provide a pathway for electricity to flow from a power source to a load, which is a device that uses electrical energy to perform a specific task. The circuit allows for the transfer of energy to power the load.

## 3. What are the components of a simple circuit?

The components of a simple circuit include a power source (such as a battery), conductors (such as wires), and a load (such as a light bulb or motor). Switches can also be added to control the flow of electricity in the circuit.

## 4. How does a simple circuit work?

A simple circuit works by using conductors to connect the positive and negative terminals of a power source, creating a closed loop for the flow of electricity. The electricity flows from the positive terminal, through the load, and back to the negative terminal of the power source.

## 5. What is the difference between a series and parallel simple circuit?

In a series circuit, the components are connected in a single path so that the current flows through each component in sequence. In a parallel circuit, the components are connected in separate branches so that the current can flow through each component independently. This results in different effects on the overall current and voltage in the circuit.

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