Voltage in Series & Parallel Circuits Lab Guide

PhysicsBeginnerReading time: 3 min

Overview

Voltage is the electric potential difference between two points in a circuit. The relationship between individual voltages and the total voltage differs significantly depending on the connection method. This experiment uses real-time voltmeters to help you explore the voltage division effect in series circuits and the equal voltage characteristic of parallel circuits.

Background

In 1845, German physicist Gustav Kirchhoff, at the age of 21, formulated the famous Kirchhoff's Voltage Law (KVL): the algebraic sum of voltage rises and drops in any closed loop is zero. This law laid the theoretical foundation for voltage division in series circuits and voltage equality in parallel circuits. In the era of telegraphy, engineers used the series voltage divider principle for long-distance signal transmission and the parallel equal voltage property to ensure stable voltage for every node. Today, these laws remain the cornerstone of electronic circuit design.

Key Concepts

Terminal Voltage

U

The voltage across a power source or circuit component. In the simulation, the total voltage is directly controlled by the power supply voltage slider.

Voltage Division

U_n \propto R_n

In a series circuit, the total voltage is distributed among the resistors. The larger the resistance, the larger the share of voltage it receives.

Equal Voltage

U_1 = U_2 = U

In a parallel circuit, the voltage across each branch is equal and is also equal to the total voltage.

Formulas & Derivation

Series Voltage Law

U = U_1 + U_2

In a series circuit, the total voltage equals the sum of the individual voltages. Energy decreases step by step as it passes through each resistor.

Parallel Voltage Law

U = U_1 = U_2

In a parallel circuit, the voltage across each branch is equal and equals the power supply voltage.

Experiment Steps

1
Setup Series Circuit
Select 'Series Circuit' on the panel. Initially, both resistors are $10\Omega$ . You can adjust $R_2$ to $20\Omega$ or another value. Close the switch and observe the readings of the three voltmeters $U$ , $U_1$ , and $U_2$ . Do $U_1$ and $U_2$ add up to $U$ ?
2
Explore Resistance Effect
In series mode, try changing the resistance of $R_1$ or $R_2$ . You will find: the part with larger resistance has a ____ voltmeter reading? This shows that series circuits distribute voltage in proportion to resistance.
3
Switch to Parallel Circuit
Switch the circuit to 'Parallel Circuit'. Observe the voltmeter readings across $R_1$ and $R_2$ . Even if the resistance values of the two branches are set differently, do their voltages remain consistent?
4
Change Total Voltage
Adjust the power supply voltage slider. Observe how the voltage across each branch in the parallel circuit changes with the total voltage. Think: What is the relationship between the branch voltages and the power supply voltage?

Learning Outcomes

Understand the additive relationship of total voltage and component voltages in series circuits
Master the physical characteristic that voltage across parallel branches is equal
Be able to predict series voltage values based on resistance ratios
Learn to use virtual voltmeters to measure potential difference in circuits

Real-world Applications

Voltage Divider Circuits: Electronic devices often use two resistors in series to obtain a lower reference voltage
Home Outlets: All appliances are connected in parallel to a 220V (or 110V) power source to ensure each receives its rated voltage
Voltmeter Range Extension: A large resistor is connected in series with the meter head to enable it to measure higher voltages

Common Misconceptions

Misconception

In a series circuit, voltage across all resistors should be equal

Correct

Incorrect. Voltage is split equally only when series resistors are equal. Different resistances result in different voltage distributions.

Misconception

In a parallel circuit, the branch with larger resistance has larger voltage

Correct

Incorrect. Voltage across parallel branches is exactly equal, regardless of resistance. Resistance only affects the current in that branch.

Ready to start?

Now that you understand the basics, start the interactive experiment!

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