Assigning Polarities and using them in KVL equation, circuits

In summary, when assigning polarities to voltage in a circuit, it is important to be consistent. There are no specific rules for assigning polarities to resistors, but it is important to ensure that the sum of the voltage rises equals the sum of the voltage drops when going around the loop. If you assign the polarities as you see fit, you may end up with a negative voltage when solving the system of equations. When putting quantities in the KVL equation, it is important to distinguish between the positive and negative polarities, which can be determined by the direction of the voltage drop or rise in the circuit. Overall, polarities play a crucial role in solving circuit problems, as they determine the direction and magnitude of voltage across components in
  • #1
wahaj
156
2
I am having trouble understanding how to assign polarities to voltage when it goes through components of a circuit and how those polarities determine the sign of the quantities I put in the KVL equation. Attached is a picture of a circuit. The points where polarity matters are labeled 1-14. I am trying to find the voltage of battery 1/2. I know how to assign polarities to batteries but are there any rules I should obey when assigning polarities to resistors? Also what happens to voltage when batteries are connected like battery 1/2 and battery 3/4 in the picture? Also when putting quantities in the kvl equation how can I determine which quantity is positive and which is negative? and lastly what role do polarities play when solving circuit problems?
 

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  • #2
It doesn't matter as long as you are consistent. If you guess wrong all that will happen is that when you solve the system of equations one of the voltages will be negative.
 
  • #3
if you assign all +/- pairs consistently going around the loop, the sum of the voltages must equal zero.

but if you assign the polarities as you see fit, then, going around the loop (either clockwise or counter-clockwise), then KVL says that the sum of the voltage rises equals the sum of the voltage drops.

both versions say the same thing.
 
  • #4
ok so when putting the voltages in the equation how do I distinguish between the two different polarities? another way to say this is how to I know when the voltage drops and when the voltage rises?
 
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  • #5


I understand your confusion about assigning polarities and using them in KVL equations for circuits. It can be a complex concept to grasp, but there are some general rules and guidelines that can help you understand and apply polarities in circuit analysis.

Firstly, when assigning polarities to voltage sources (such as batteries), the convention is to assign the positive terminal as the higher potential and the negative terminal as the lower potential. This is important because it helps us maintain consistency in the direction of current flow in the circuit. For example, in the circuit shown in the picture, the positive terminal of battery 1/2 should be assigned as the higher potential and the negative terminal as the lower potential.

When it comes to resistors, the polarity assignment is not as important as it is for voltage sources. This is because resistors do not have a specific direction of current flow, unlike voltage sources. However, a general rule is to assign the polarity of a resistor based on the direction of current flow in the circuit. For example, if the current is flowing from the positive terminal of a voltage source to the negative terminal, then the polarity of the resistor should be assigned in the same direction.

In the specific case of batteries connected in series (like battery 1/2 and battery 3/4 in the picture), the total voltage across the two batteries will be the sum of their individual voltages. This means that the negative terminal of battery 1/2 will be connected to the positive terminal of battery 3/4, and the remaining two terminals will be the positive and negative terminals of the combined battery. This concept is known as Kirchhoff's Voltage Law (KVL).

When solving circuit problems, the polarities of voltage sources and resistors play a crucial role in determining the direction and magnitude of current flow in the circuit. This information is then used to calculate the voltage drop across each component using Ohm's Law and to apply KVL to solve for unknown voltages.

In summary, the assignment of polarities in circuits helps us maintain consistency in the direction of current flow and is essential in applying laws such as Ohm's Law and KVL. I hope this explanation helps you better understand how to assign polarities and use them in KVL equations for circuit analysis.
 

What is the purpose of assigning polarities in circuit analysis?

The purpose of assigning polarities in circuit analysis is to establish a reference direction for the current flow. This reference direction is used to determine the signs (+ or -) of the voltage drops across circuit elements in the Kirchoff's Voltage Law (KVL) equation.

How do you assign polarities in a circuit?

Polarities are assigned by choosing a reference direction for the current flow in the circuit. This is typically done by selecting a starting point and following the current flow direction through the circuit. The chosen direction is then used to determine the signs of the voltage drops across circuit elements in the KVL equation.

What is Kirchoff's Voltage Law (KVL) equation?

Kirchoff's Voltage Law (KVL) is a fundamental law in circuit analysis that states that the sum of all voltage drops in a closed loop circuit is equal to the sum of all voltage sources in the same loop. This law is based on the principle of conservation of energy and is used to analyze circuits and solve for unknown voltages.

How do you use polarities in the KVL equation?

Polarities are used in the KVL equation by assigning a positive (+) sign to voltage drops in the direction of the current flow and a negative (-) sign to voltage drops in the opposite direction. This ensures that the sum of all voltage drops in a closed loop is equal to the sum of all voltage sources in the same loop, as stated by Kirchoff's Voltage Law.

What happens if you assign incorrect polarities in a circuit?

If incorrect polarities are assigned in a circuit, the resulting KVL equation will be incorrect and may lead to incorrect solutions. It is important to carefully assign polarities in the correct direction to ensure accurate circuit analysis and solution. Additionally, incorrect polarities may result in negative voltage values, which can be physically impossible in a circuit.

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