Current in Series & Parallel Circuits Lab Guide

PhysicsBeginnerReading time: 3 min

Overview

The flow of electric charge follows strict conservation laws. In a series circuit, there is only one path for the current; in a parallel circuit, the current divides into multiple paths. This experiment will help you discover the current rules in series and parallel circuits through real-time simulation and data comparison.

Background

Voltaic Pile: In 1800, Volta invented the battery, making the study of steady electric currents possible.
Kirchhoff's Laws: In 1845, Gustav Kirchhoff proposed circuit laws that rigorously described the conservation relationships of node currents and loop voltages.
Electrification Era: Edison initially promoted direct current (DC) networks (focusing on parallel loads), while Tesla promoted alternating current (AC), eventually laying the foundation for modern power systems.

Key Concepts

Series Circuit

\text{Single Path}

A circuit where components are connected one after another. Current flows from the positive terminal, through all components, and back to the negative terminal.

Parallel Circuit

\text{Multiple Paths}

A circuit where components are connected side by side between two points. Current divides into multiple paths at a junction (node).

Main Current

I_{\text{total}}

In a parallel circuit, the total current before splitting or after recombining. It is like the main channel of a river.

Branch Current

I_1, I_2

In a parallel circuit, the current flowing through each individual branch. The sum of branch currents equals the main current.

Formulas & Derivation

Series Current Law

I = I_1 = I_2

In a series circuit, the current is the same everywhere. Since there is only one path, the amount of charge passing through each component is identical.

Parallel Current Law

I = I_1 + I_2

In a parallel circuit, the main current equals the sum of the branch currents. This demonstrates the law of conservation of charge.

Experiment Steps

1
Observe Series Current
Select "Series Circuit" in the control panel. Set $R_1=10\Omega$ , $R_2=20\Omega$ , and close the switch. Observe the readings of ammeters $I$ , $I_1$ , and $I_2$ . Are the currents exactly the same, even though the resistances are different?
2
Switch to Parallel Circuit
Switch the circuit to "Parallel Circuit". Observe how the current splits in the circuit diagram. What is the relationship between the main current and the branch currents?
3
Explore Parallel Current Splitting
In parallel mode, keep $R_1=10\Omega$ constant and try increasing the resistance of $R_2$ . Observe the changes in $I_1$ and $I_2$ . The larger the branch resistance, the ____ the current it receives?
4
Verify Total Current Formula
Record the readings of $I_1$ and $I_2$ at a certain moment and calculate if their sum equals the total current $I_{total}$ . Try changing the power supply voltage to see if this rule still holds.

Learning Outcomes

Learn to distinguish between the structural characteristics of series and parallel circuits.
Experimentally verify the rule that current is the same everywhere in a series circuit.
Experimentally verify the rule that the main current equals the sum of branch currents in a parallel circuit.
Understand the effect of resistance on current splitting in parallel circuits: larger resistance leads to smaller current.

Real-world Applications

Home Circuits: Sockets and lights are usually connected in parallel, ensuring that if one light fails, the others remain lit, and each device can draw current from the main supply.
Decorative Lights: Old-style string lights used series connections, so if one bulb failed, the entire string would go out.
Car Dashboard: Various sensors and indicators are connected in parallel so they do not interfere with each other.

Common Misconceptions

Misconception

In a series circuit, the current gets "used up" and becomes smaller after passing through a resistor.

Correct

Incorrect. Current is the flow of charge, and charge is not consumed when passing through a resistor. The current intensity is exactly the same at every point in a series circuit.

Misconception

In a parallel circuit, the current in each branch is always equal.

Correct

Not necessarily. Current only splits equally if the resistance in each branch is the same. A branch with higher resistance will receive less current.

Ready to start?

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

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