Someone with knowledge of parallel circuits please help

[StrongBad42]

I have a project due in a couple days, and I'm just not good with circuits. I keep shorting the circuit, through one of the ammeters.

Here are the instructions:

Place two resistors, two ammeters and a battery onto the work space.
Set the battery voltage to 12 volts.
Set one resistor to a resistance of 3 Ohms and the other to a 30 Ohms
Connect the two resistors in parallel , include the one ammeter so that it measures the total current flow of the circuit.
Set the other ammeter so that it measures the current flow in the 30 Ohm branch of the circuit.
Connect the battery (electrons should now be flowing.)

And here is the website we are using to construct the circuits.
http://phet.colorado.edu/en/simulation/circuit-construction-kit-ac

If someone could post a screenshot of the completed circuit, i'd be extremely grateful.

 

[Rhumbline]

There are a couple ways to rig this. Here's one, sorry, no pic.

The positive lead from the battery should go to one lead on each of the resistors. The second lead on each of the resistors should go to one lead on an ammeter. The second lead on the ammeter should go to the negative lead on the battery.

So, circuit one = battery Positive to resistor1 to ammeter1 to battery negative.
Circuit two = battery Positive to resistor2 to ammeter2 to battery negative.

ETA: the current in the 3 ohm circuit will be 4 amps, in the 30 Ohm circuit .4 amps

 

[StrongBad42]

Thanks for the reply. I set it up the way you said, and it's working fine, except i'm not getting the numbers you gave. According to the instructions, one of the ammeters is supposed to measure the total current flow of the circuit. Is that possible on a parallel? Is the 4 amp ammeter doing that?

Edit: I got it working with the numbers you gave now.

 

[Rhumbline]

Thanks for the reply. I set it up the way you said, and it's working fine, except i'm not getting the numbers you gave. According to the instructions, one of the ammeters is supposed to measure the total current flow of the circuit. Is that possible on a parallel? Is the 4 amp ammeter doing that?

Edit: I got it working with the numbers you gave now.

I'm happy to hear that.

Now, tell the class what the overall power consumption of the circuit is.

 

[N7KMS]

I'm happy to hear that.

Now, tell the class what the overall power consumption of the circuit is.

Current is additive in parallel so over all current would be 4.4 amps. I guess saying it is additive may not be 100% accurate, but the current divides along each path in the circuit and more current will take the path of less resistance (as indicated by Ohms Law and Kirchoffs Second Law). To measure the total current of the circuit you would put a meter in series between the junction of the parallel resistors and the power source and it should read 4.4 amps. You can verify that mathematically by calculating your resistance (30x3)/(30+3) to be 2.72 ohms, 12 volts divided by 2.72 ohms = 4.4 amps.

 

[Rhumbline]

Correct, and since P=E*I, the circuit consumes 52.8 watts.

 

[Bobby_M]

Man, technology is awesome. I didn't have java circuit builders back in 95. We had to actually build it in components and let the smoke out if we got it wrong.

 

[N7KMS]

We had to actually build it in components and let the smoke out if we got it wrong.

Even to this day, I know exactly what it is when I catch a whiff of burned up ICs and resistors.

 

[Rhumbline]

Man, technology is awesome. I didn't have java circuit builders back in 95. We had to actually build it in components and let the smoke out if we got it wrong.

95? try '79! What the hell is a JavaScript? I = E/R

Would anyone really have had to build this to come up with the answer?

Now, when we get into LC circuits I'll need some scratch paper.

 

[N7KMS]

95? try '79! What the hell is a JavaScript? I = E/R

Would anyone really have had to build this to come up with the answer?

Now, when we get into LC circuits I'll need some scratch paper.

The voltage and resistances were given in the description, and you know its in parallel so you can calculate the total resistance. Even back in the early 2000s though when I was learning all this we did it all on breadboards and with variable power supplies and benchtop multimeters. One of my first programs I wrote in perl was an Ohms Law calculator.

I just recently passed my Extra Class ham license so the LC and RC and resonance and reactance and filters and junk is all still fresh in my head.

 

[Rhumbline]

...

I just recently passed my Extra Class ham license so the LC and RC and resonance and reactance and filters and junk is all still fresh in my head.

Congratulations, that's an accomplishment to be proud of. I thought you might be a ham with that forum name.

I never pursued the license, there was no way I was going to learn Morse code. I worked with enough of those guys in the service and I think it permanently rewired their brains.

I understand they've dropped the Morse requirement? Or did they come up with a new classification?

 

[IslandLizard]

There are a couple ways to rig this. Here's one, sorry, no pic.

The positive lead from the battery should go to one lead on each of the resistors. The second lead on each of the resistors should go to one lead on an ammeter. The second lead on the ammeter should go to the negative lead on the battery.

So, circuit one = battery Positive to resistor1 to ammeter1 to battery negative.
Circuit two = battery Positive to resistor2 to ammeter2 to battery negative.

ETA: the current in the 3 ohm circuit will be 4 amps, in the 30 Ohm circuit .4 amps

I hate to bring bad news, but this does not solve the problem as posed.
The 2nd ammeter should measure the total circuit current:

Circuit two = battery Positive to ammeter2 to both resistor1 (30 ohm) and resistor2 (3 ohm). Then resistor2 to battery negative.

This is after one cup of Java.

 

[N7KMS]

CI understand they've dropped the Morse requirement? Or did they come up with a new classification?

They did drop the morse code requirement a couple years ago and restructured the frequency privileges for the license classes. Nowadays the entry level Technician licenses get some voice and CW on the 10 meter band and CW only on a couple other HF bands so that opens up the possibilities of working DX to newcomers.

 

[Rhumbline]

I hate to bring bad news, but this does not solve the problem as posed.
The 2nd ammeter should measure the total circuit current:

Circuit two = battery Positive to ammeter2 to both resistor1 (30 ohm) and resistor2 (3 ohm). Then resistor2 to battery negative.

This is after one cup of Java.

You're right, I misread the original post.