Resistors in Parallel Questions

rdb1

Joined Feb 6, 2019
54
I have some questions that I am just going over. One of them is as follows:

Three resistors connected in parallel across a 2.4-volt d.c supply
• 0.012 ohms
• 0.015 ohms
• 0.008 ohms
Questions are:

1. Current flowing through each resistor.
2. Current in each section of the circuit
3. Total Current drawn from the supply
For question 1 I used OHMS Law I1 1A, I2 1/3A I3 2/3 A. I am not sure what it means by question two and for Question 3 is it the Supply Current minus the Total Current?

MOD NOTE: Removed second problem to avoid confusion.

Last edited by a moderator:

crutschow

Joined Mar 14, 2008
23,782
I used OHMS Law I1 1A, I2 1/3A I3 2/3 A.
Show us how you used Ohm's law to get those values, which are not correct.

WBahn

Joined Mar 31, 2012
24,974
It's generally not a good idea to discuss more than one problem in the same thread. Inevitably some people will respond about one problem right after someone else responded about the other and chaos and confusion quickly take over. So pick one. Discuss it in this thread. Then, once that one is resolved, if you still can't work the other, start a new thread about it.

WBahn

Joined Mar 31, 2012
24,974
I have some questions that I am just going over. One of them is as follows:

Three resistors connected in parallel across a 2.4-volt d.c supply
• 0.012 ohms
• 0.015 ohms
• 0.008 ohms
Questions are:

1. Current flowing through each resistor.
2. Current in each section of the circuit
3. Total Current drawn from the supply
For question 1 I used OHMS Law I1 1A, I2 1/3A I3 2/3 A. I am not sure what it means by question two and for Question 3 is it the Supply Current minus the Total Current?

MOD NOTE: Removed second problem to avoid confusion.
Show your work to get each of those currents.

One thing you want to get into the habit of doing ALL THE TIME is asking if your results make sense.

How much current would flow in a 1 Ω resistor connected to a 2.4 V DC supply?

So, does it make sense that if you decrease the resistance significantly that the current would go down?

Just looking at your answers, does it make sense that the current in the smallest resistor would be half of the current in the largest or that the current in the middle-valued resistor would have the highest current (i.e., there is a larger resistor and a smaller resistor and both of them have less current)?

Question #2 probably refers to the specific circuit layout given. Did you have a schematic that came with the problem?

rdb1

Joined Feb 6, 2019
54
Show us how you used Ohm's law to get those values, which are not correct.
How I got the current was doing divide Voltage in this case 2.4 by the resistance of each
• 0.012 ohms to get 1A.
Or do I need to convert 2.4 volts 2400?

rdb1

Joined Feb 6, 2019
54
Show your work to get each of those currents.

One thing you want to get into the habit of doing ALL THE TIME is asking if your results make sense.

How much current would flow in a 1 Ω resistor connected to a 2.4 V DC supply?

So, does it make sense that if you decrease the resistance significantly that the current would go down?

Just looking at your answers, does it make sense that the current in the smallest resistor would be half of the current in the largest or that the current in the middle-valued resistor would have the highest current (i.e., there is a larger resistor and a smaller resistor and both of them have less current)?

Question #2 probably refers to the specific circuit layout given. Did you have a schematic that came with the problem?
There is no schematic, its just a list of bullet points.

WBahn

Joined Mar 31, 2012
24,974
How I got the current was doing divide Voltage in this case 2.4 by the resistance of each
• 0.012 ohms to get 1A.
Or do I need to convert 2.4 volts 2400?
So you are saying that if you divide 2.4 by 0.012 you get 1?

Not on MY calculator!

WBahn

Joined Mar 31, 2012
24,974
There is no schematic, its just a list of bullet points.
Then the second question is extremely ambiguous.

The third question, though, is just fine. What is the total current drawn from the supply?

What do YOU mean by "total current" and why would you subtract it from the supply current when you are being asked FOR the supply current?

rdb1

Joined Feb 6, 2019
54
So you are saying that if you divide 2.4 by 0.012 you get 1?

Not on MY calculator!
Sorry, my mistake I have got the correct values:

I1 is 200A
I2 160A
I3 is 300A

rdb1

Joined Feb 6, 2019
54
Then the second question is extremely ambiguous.

The third question, though, is just fine. What is the total current drawn from the supply?

What do YOU mean by "total current" and why would you subtract it from the supply current when you are being asked FOR the supply current?
The total current is what I1+I2+I3 but its asking for the total current drawn from the supply.

WBahn

Joined Mar 31, 2012
24,974
Sorry, my mistake I have got the correct values:

I1 is 200A
I2 160A
I3 is 300A
Much better.

Hopefully you are recognizing that you have a serious "number sense" deficiency.

Anytime you get an answer of 1 when dividing one number by another, a HUGE red flag and LOUD warning bells should go off if the two numbers aren't the same. If you continue to just blindly write down the answer and push on, you are highly unlikely to ever successfully solve any problem of any complexity.

I once convinced a 16 year old girl that she was only 14 because she believed whatever a calculator told her -- and I have witnesses.

WBahn

Joined Mar 31, 2012
24,974
The total current is what I1+I2+I3 but its asking for the total current drawn from the supply.
Where do you think that I1 + I2 + I3 comes from?

rdb1

Joined Feb 6, 2019
54
Much better.

Hopefully you are recognizing that you have a serious "number sense" deficiency.

Anytime you get an answer of 1 when dividing one number by another, a HUGE red flag and LOUD warning bells should go off if the two numbers aren't the same. If you continue to just blindly write down the answer and push on, you are highly unlikely to ever successfully solve any problem of any complexity.

I once convinced a 16 year old girl that she was only 14 because she believed whatever a calculator told her -- and I have witnesses.
I realised that they were the wrong numbers. But its always good to double check.

rdb1

Joined Feb 6, 2019
54
Where do you think that I1 + I2 + I3 comes from?
I guess I am referring to this:
The sum of the currents through each path is equal to the total current that flows from the source

WBahn

Joined Mar 31, 2012
24,974
I guess I am referring to this:
The sum of the currents through each path is equal to the total current that flows from the source

WBahn

Joined Mar 31, 2012
24,974
How do you mean?

How do you mean confusing? Its from this: https://www.swtc.edu/Ag_Power/electrical/lecture/parallel_circuits.htm

You have the total current used by the resistors, namely I1 + I2 + I3, but don't seem to see that this total current has to be coming from the supply and such that the current drawn from the supply is also I1 + I2 + I3.

Try drawing and labeling a schematic. It will probably help quite a bit.

rdb1

Joined Feb 6, 2019
54

You have the total current used by the resistors, namely I1 + I2 + I3, but don't seem to see that this total current has to be coming from the supply and such that the current drawn from the supply is also I1 + I2 + I3.

Try drawing and labelling a schematic. It will probably help quite a bit.
It may just be the way it has been worded and it has thrown me ofI'veIve just known that I need to find the total current. But the way you have phrased it makes sense. I may do that. I think I will leave the second question as I am not sure about that at all. As you say its a bit ambiguous without a schematic.

So the answer to Question 3 would be 660A

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WBahn

Joined Mar 31, 2012
24,974
It may just be the way it has been worded and it has thrown me ofI'veIve just known that I need to find the total current. But the way you have phrased it makes sense. I may do that. I think I will leave the second question as I am not sure about that at all. As you say its a bit ambiguous without a schematic.

So the answer to Question 3 would be 660A
Most likely. But now confirm it be finding the equivalent resistance and using that to find the total current.

rdb1

Joined Feb 6, 2019
54
Most likely. But now confirm it be finding the equivalent resistance and using that to find the total current.
Ive done that by using I X R

I1 200A X 0.012 Ohms I get 2.4
I2 160A X 0.015 Ohms I get 2.4
I3 300A X 0.008 Ohms I get 2.4

I have tried drawing a schematic, but its not helped with the second question, so I will leave that for now, and ask the tutor for advice.