# Potential Change in a Circuit Diagram

• daimoku
In summary, the problem involves finding the potential at point Q in a circuit diagram, given that the potential at point P is 400 V. Using Ohm's Law and the fact that the sum of potential changes in a circuit must be zero, the solution involves finding the current (20A) and using it to calculate the potential at point Q (290V).

#### daimoku

[SOLVED] Potential Change in a Circuit Diagram

## Homework Statement

http://personalpages.tds.net/~locowise/test/28_29.gif

If the potential at point P is 400 V, what is the potential at point Q?

## Homework Equations

Ohm's Law: deltaV=iR
Probably the fact that the sum of changes in potential in a loop of any circuit must be zero.

## The Attempt at a Solution

Not real sure on this problem. I tried this:
150V - 2.0i - 3.0i - 50V = 0V and found i to be 20A.

I'm kind of puzzled and can't seem to relate the material in the textbook to this problem. Where does the 400V potential come into play? Thanks for your help!

Last edited by a moderator:
I'm still not really sure this is the proper way to approach the problem but apparently the solution is correct. Here's what I did:

Used 20A from above.

400V - 50V - 3.0ohms * 20A = 290V

I understand your confusion with this problem. It appears that the potential at point P is not directly related to the potential at point Q. However, it is important to note that the potential difference between any two points in a circuit is determined by the sum of the changes in potential along the path connecting those two points. In this case, the potential difference between points P and Q is equal to the potential difference between points P and A, plus the potential difference between points A and B, plus the potential difference between points B and C, plus the potential difference between points C and Q.

Using Ohm's Law, we can calculate the potential difference between points P and A as 150 V, and the potential difference between points A and B as 2.0i, where i is the current flowing through the circuit. Similarly, the potential difference between points B and C can be calculated as 3.0i, and the potential difference between points C and Q can be calculated as 50 V.

Therefore, the potential difference between points P and Q can be written as:

deltaV(PQ) = 150 V + 2.0i + 3.0i + 50 V

Since we know that the potential at point P is 400 V, we can set this equal to the potential difference between points P and Q and solve for i:

400 V = 150 V + 2.0i + 3.0i + 50 V

Simplifying, we get:

400 V = 200 V + 5.0i

Solving for i, we get i = 40 A.

Therefore, the potential at point Q is equal to the potential at point C, which can be calculated as:

deltaV(PQ) = 50 V + 3.0(40 A) = 170 V

In conclusion, the potential at point Q is 170 V. I hope this helps clarify the problem for you.

## 1. What is a potential change in a circuit diagram?

A potential change in a circuit diagram refers to a difference in electrical potential between two points in a circuit. This difference in potential can be caused by various factors such as the presence of a battery, a change in resistance, or the connection of additional components.

## 2. How is a potential change represented in a circuit diagram?

A potential change is represented in a circuit diagram by the use of symbols and labels. The symbol for a battery or power source is typically a long line with a shorter line and a plus sign, while resistance is represented by a zigzag line. The labels on the diagram indicate the exact values of potential changes and other components in the circuit.

## 3. What are the units of measurement for potential change in a circuit diagram?

The units of measurement for potential change in a circuit diagram are volts (V) or millivolts (mV). Volts are the standard unit of measurement for electric potential, while millivolts are used for smaller changes in potential.

## 4. How does a potential change affect the flow of electricity in a circuit?

A potential change affects the flow of electricity in a circuit by creating a driving force for the electrons to move through the circuit. The greater the potential difference, the stronger the driving force and the faster the electrons will flow through the circuit.

## 5. Can potential changes be controlled in a circuit?

Yes, potential changes can be controlled in a circuit through the use of components such as resistors, capacitors, and diodes. These components can alter the flow of electricity and adjust the potential difference between different points in the circuit.