# Physics 2 exam tomorrow. Need help with a couple more problems and im good

• LakeMountD
In summary, Daniel is trying to figure out a circuit and explain how it works. He is having trouble with two problems and is asking for help. The first problem is that he cannot solve for the current using relevant formulae. The second problem is that two resistors are connected in series and the current does not stay the same. He needs to find the circuit's impedance and the current and then find the tensions across each side of the square.
LakeMountD
Physics 2 exam tomorrow. Need help with a couple more problems and I am good! :)

1. a circuit has a 137 mH inductor across AB (the whole curcuit is a square with corners ABCD), a 50 ohm resistor across BC, and a 25 uF capacitor across CD with a 115V @ 60 hz power source between DA. What is the rms voltage across points AB, BC, CD, AC, and BD . I CANT FIGURE ANY OF THESE ONES OUT! They are driving me and like 4 other people crazy.

2. Two resistors are connected in series across a potential differencfe. Resistor A has twice teh resistance of resistor B. If the current carried by resistor A is I, then what is the current carried by resistor B? The answer is Just a) I but I can't seem to solve for it mathematically using relevant formulae.

For the second problem,how is a series connection of resistors defined and what consequences does it have...?

For the first,what does "rms voltage" mean??

Daniel.

dextercioby said:
For the second problem,how is a series connection of resistors defined and what consequences does it have...?

For the first,what does "rms voltage" mean??

Daniel.

rms voltage is root-mean square voltage.. I know in series the voltage changes but the current stays the same throughout the curcuit. I just do the proofs with the formulas to show it.

Conservation of electric charge insures the current stays the same in a series connection.

For the first problem,compute the circuit's impedance.Then the current (the amplitude) and then the tensions across each side of the square.

Daniel.

LakeMountD said:
1. a circuit has a 137 mH inductor across AB (the whole curcuit is a square with corners ABCD), a 50 ohm resistor across BC, and a 25 uF capacitor across CD with a 115V @ 60 hz power source between DA. What is the rms voltage across points AB, BC, CD, AC, and BD . I CANT FIGURE ANY OF THESE ONES OUT! They are driving me and like 4 other people crazy.

2. Two resistors are connected in series across a potential differencfe. Resistor A has twice teh resistance of resistor B. If the current carried by resistor A is I, then what is the current carried by resistor B? The answer is Just a) I but I can't seem to solve for it mathematically using relevant formulae.

1) You have a series RLC circuit. You should have learned how to calculate the impedence of any single one of those three devices, and the impedence of the three of them in combination. The combination will allow you to determine the current being delivered by the power source, and the individual impedences will can then be used to find the voltages.

2) Charge is not created or destroyed, and ideal resistors cannot store charge. Where can the current flowing through RA go?

OOPs collision in cyberspace

We are both saying the same thing. Take your pick

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OlderDan said:
1) You have a series RLC circuit. You should have learned how to calculate the impedence of any single one of those three devices, and the impedence of the three of them in combination. The combination will allow you to determine the current being delivered by the power source, and the individual impedences will can then be used to find the voltages.

2) Charge is not created or destroyed, and ideal resistors cannot store charge. Where can the current flowing through RA go?

OOPs collision in cyberspace

We are both saying the same thing. Take your pick

on number 1- z=74 ohms
XL= 51.6 ohms

I= Vapp,peak/Z= 1.49 amps

Vrms,L = XL * I = 77 volts

and i did same thing for the resistor and capacitor and get right answer
HOWEVER- what do i have to do when going from AC or BD ? i tried combining the voltagse and then tried calculating a new voltage after first one and applying it to the second and both yielded wrong answers.

well on number 2 i understand why the answer is what it is. but proving it mathematically is another story. he wants it to come down to everything cancelling out in the end and the equations reduct to I1=I2 and we just can't seem to do the proof.

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I only have time for a quick comment here. What you must keep in mind is that the voltages across the three devices in the circuit are not in phase. While at any point in time the true voltages in the loop must add up to zero, the rms voltages need not add up to zero. The current is the common thing to all elements in the circuit. That is why you must find the total current from the total impedence first, and then go back and figure out the individual voltages using that current.

## 1. How can I prepare for my Physics 2 exam tomorrow?

To prepare for your exam, it is important to review all of the material that will be covered. This includes going over your notes, textbook readings, and any practice problems or quizzes. It may also be helpful to study with a group or seek help from a tutor if you are struggling with certain concepts.

## 2. What are some common topics that are covered on a Physics 2 exam?

Some common topics that may be covered on a Physics 2 exam include electromagnetism, thermodynamics, optics, and atomic and nuclear physics. It is important to review all of these topics thoroughly to ensure you are prepared for the exam.

## 3. How can I improve my problem-solving skills for my Physics 2 exam?

One way to improve your problem-solving skills is to practice solving different types of problems. You can also try breaking down complex problems into smaller, more manageable parts. Additionally, make sure you understand the concepts behind the problems rather than just memorizing formulas.

## 4. What resources are available to help me with my Physics 2 exam preparation?

There are many resources available to help you prepare for your exam. Your textbook, class notes, and online resources can all be helpful tools. You can also seek help from your professor, teaching assistant, or a tutor for additional assistance.

## 5. I am struggling with a few specific problems, where can I find help?

If you are struggling with specific problems, consider seeking help from your professor, teaching assistant, or a tutor. You can also try reaching out to classmates or forming a study group to work through the problems together. Additionally, there are many online resources and practice problems available for extra help.

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