Just by “Holding” the Connection?! The Voltage Experiment That Suddenly Produced Shockingly Perfect Data (The Hidden Nature of Voltage)
I’m Ken Kuwako, the Science Trainer. Every day is an experiment.
Electricity is invisible, yet a tiny change in how you connect a circuit can completely transform its behavior. Connect components in series or in parallel, and suddenly the voltage behaves in entirely different ways. In this lesson, we used real experimental data to reveal those hidden patterns with surprising clarity. The results lined up so beautifully that I couldn’t help blurting out during class, “This is gorgeous!” Meanwhile, my students just stared at me in silence.
Warming Up — Learning How to Use a Digital Voltmeter
Before diving into the main experiment, we reviewed how to use a digital voltmeter. Students built a simple circuit using a single 20-ohm resistor and a 3V power supply, then measured both the voltage across the resistor and the voltage across the power source.
Some groups got perfectly matching values. Others were slightly off.
So we tried something simple: gently squeezing the circuit connections with our fingers.
And suddenly, the readings became much more consistent.
This highlights an important truth about electric circuits: poor connections create measurement errors. Even a microscopic gap between a wire and a terminal can create extra “contact resistance,” which throws off voltage measurements.
By squeezing the connection, the contact area increases and the resistance drops. It’s a tiny action, but it makes a huge difference.
From this, students learned several important habits before starting any experiment:
・After building a circuit, check and adjust every connection before measuring.
・Complete the entire circuit properly before taking voltage readings one by one.
・Each group gets one voltmeter, so measurements should be taken carefully and in order.
Making Predictions Before the Experiment — This Time Using Equations
The main topic of the day was the rules governing voltage in series and parallel circuits.
Before starting the experiment, each group came up with a hypothesis. Unlike previous current experiments, this time students shared their ideas only within their own groups instead of with the whole class.
And there was one more condition: hypotheses had to be written using equations, not vague guesses.
Expressions like V₁ + V₂ = V made it much easier to compare predictions with the actual data later.
The experiment used two resistors: 10 ohms and 20 ohms.
Time to test the theory.
Results for the Series Circuit — The Numbers Added Up Perfectly
All class data was collected into a single shared spreadsheet, and every student entered their own measurements. By combining results from eight groups instead of relying on just one experiment, patterns became much easier to see.
And the pattern was stunningly clear.
Voltage across resistor A + voltage across resistor B = source voltage
Every single group showed the same relationship.
In a series circuit, voltage is divided according to resistance. Since the resistors were 10 ohms and 20 ohms — a ratio of 1:2 — the voltage should also divide in a 1:2 ratio.
And that is exactly what the data showed.
Electrical energy gets “used up” as current flows through each resistor. The energy supplied by the battery is gradually consumed, and by the time the current returns, the total energy drop matches the source voltage perfectly.
That’s the beauty of voltage in a series circuit.
Results for the Parallel Circuit — Everything Was the Same!
Next came the parallel circuit.
Once again, the data lined up beautifully.
The source voltage, resistor A voltage, and resistor B voltage were all nearly identical.
In a parallel circuit, each resistor is connected directly to the power source. That means every branch receives the same voltage.
A perfect real-world example is the electrical outlets in your home. Your TV, refrigerator, and lights all run on the same 100V supply. That’s possible because household wiring is connected in parallel.
Why Was the Data So Surprisingly Clean This Time?
Honestly, this experiment usually produces messy results. The patterns can be hard to spot because the measurements often scatter quite a bit.
For example, here’s data from a previous parallel circuit experiment.
The variation is obvious, making the underlying rule difficult to recognize.
But this time, the results were probably the clearest we’ve ever had.
There seem to be two main reasons:
First, students became conscious of “squeezing” the connections. That reduced contact resistance and stabilized the readings.
Second, we replaced the old wires with new ones. Worn-out wires can develop internal damage or unstable contacts as insulation deteriorates over time.
It was a great reminder that the condition of your equipment can dramatically affect the quality of experimental data.
References
・Here is the spreadsheet used in the experiment. It is view-only, so please make your own copy before using it.
・For previous experiment records, see below.
Series Circuit
Parallel Circuit
・Reference: Previous lessons in this unit
- Pencil Circuit — Lesson 1
- How to Draw Circuit Diagrams — Lesson 2
- How to Use an Ammeter — Lesson 3
- What Happens to Current Before and After a Light Bulb? — Lesson 4
- Current Rules — Series and Parallel Circuits — Lesson 5
- From Analog to Digital Voltmeters — Lesson 6
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Science should feel exciting and close to everyday life! This site shares fun science experiments you can try at home, along with easy-to-understand explanations and tips. Feel free to explore around!
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