# Formula to get voltage on circuit

Discussion in 'Electronics Homework Help' started by olakease, May 12, 2014.

1. ### olakease

2
0
May 12, 2014
Maybe this is a Do my Homework question, but I'm learning Electronics and I'm confused on solve a simple Circuit.

The value in Voltimeter is 2.25 V, but, how can I get this value with Analysis? I mean, exists a formula for this?

2. ### KrisBlueNZSadly passed away in 2015

8,393
1,270
Nov 28, 2011
Yes, this does look like a homework question. I've moved it to the homework forum.

The first thing to do is to redraw that confusing diagram in a more familiar way.

Now you can see that the batteries are in series, and the resistors form a voltage divider across their combined voltage.

If you use the bottom line of the diagram as the 0V reference, you should be able to figure out the voltages on each side of the "V?" marking, and confirm that the difference between them is 2.25V. Then try to convert the formulas you used to calculate the voltages on each side, into a single formula that calculates the voltage difference.

I've identified the two voltage sources and the two resistors. Your formula should use those references, so that you can change the voltages and/or the resistances and the formula will still work.

olakease likes this.
3. ### nges

16
1
Feb 21, 2014
the value on the meter can be calculated using thevenin or norton or millman or .. theorems. but using the millmans method we have:

Vm= (6/5-1.5/5)/(1/5+1/5)=(6*5+5*1.5)/(5+5)=2.25V

olakease likes this.
4. ### olakease

2
0
May 12, 2014
Thank you for your replies, I will apply this.

5,165
1,087
Dec 18, 2013
Or what about (6V-1.5)/2 = 2.25V. Subtract the lower battery voltage from the top battery and replace the bottom battery with a short. Then you just have to work out the potential where the two resistors are joined in the middle with respect to 0V. This is just a simple potential divider and because the two resistors are the same value it is just the new battery voltage 4.5Volts divided buy 2.
Thanks

6. ### KrisBlueNZSadly passed away in 2015

8,393
1,270
Nov 28, 2011
As you can see, there are several ways of looking at this problem. My brain works best when I can identify a 0V rail, and it's the most negative part of the circuit (in most cases), so all other voltages are positive (or at least, non-negative) relative to it. Which approach is best depends on how you think, I guess.