Draw Circuit Diagram: 2 Dry Cells & 2 Light Bulbs in Parallel

[chemistrykid]

Q: Use symbols to draw a circuit diagram showing two dry cells connected in parallel with each other, and in parallel with two light bulbs. Show a voltmeter connected to measure the electrical potential of the two dry cells and an ammeter to measure electrical current through one of the bulbs.

A: The thing that trips me up about this question is the parallel with two light bulbs. I understand how to connect two dry cells in parallel but how do you add the light bulbs in?

 

[berkeman]

Connecting two batteries (or other voltage sources) in parallel is a bad idea. Good way to start a fire. Whatever.

Draw a horizontal line at the top of the page and one at the bottom of the page. These will be your V+ and Ground rails, respectively. For each battery, connect the + lead to the top line and the - lead to the bottom line. (Optional -- Add a note to the drawing that this is a bad way to connect batteries.) Then connect each light bulb between the two rails. Connect the voltmeter + lead to the top rail and the - lead to the bottom rail. To show the ammeter, erase part of the line between the left light bulb and the + rail, and draw a circle to represent the ammeter there. Connect the + lead of the ammeter to the top rail, and the - lead to the top lead of the light bulb.

Quiz Question -- Why is it a very bad idea to connect the two batteries in parallel?

 

[quicknote]

To connect two dry cells in parallel, we would simply connect the positive terminal of one cell to the positive terminal of the other cell, and the negative terminal of one cell to the negative terminal of the other cell. This creates a parallel circuit, where the current can flow through both cells at the same time.

To add the two light bulbs in parallel, we would connect the positive terminal of one bulb to the positive terminal of one of the dry cells, and the negative terminal of the other bulb to the negative terminal of the other dry cell. This creates a parallel branch in the circuit, where the current can flow through both bulbs at the same time.

The circuit diagram would look something like this:

[+] Dry Cell [-] --- [+] Dry Cell [-]
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[+] Bulb [-] [+] Bulb [-]

To measure the electrical potential of the two dry cells, we would connect a voltmeter in parallel with the cells. This means connecting the positive terminal of the voltmeter to the positive terminal of one cell, and the negative terminal of the voltmeter to the negative terminal of the other cell.

To measure the electrical current through one of the bulbs, we would connect an ammeter in series with the bulb. This means connecting the ammeter in between the positive terminal of the bulb and the positive terminal of the dry cell connected to it.

The circuit diagram with the voltmeter and ammeter would look like this:

[+] Dry Cell [-] --- [+] Dry Cell [-]
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[+] Bulb [-] [+] Bulb [-]
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[V] Voltmeter [A] Ammeter

Overall, this circuit diagram shows two dry cells connected in parallel with each other, and in parallel with two light bulbs. The voltmeter is connected to measure the electrical potential of the dry cells, while the ammeter is connected to measure the electrical current through one of the bulbs.