DIY Young's Double Slit with Laser Pointers: Wave Nature of Light for H2 Physics

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05 Aug 2025, 00:00 Z

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

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Q: What does DIY Young's Double Slit with Laser Pointers: Wave Nature of Light for H2 Physics cover?
A: Build genuine two-slit setups from twin hairs, razor blades or pencil leads, then measure laser wavelengths to ±2 nm, analyse fringe visibility.

TL;DR
Turn a $5 laser pointer into a quantum demonstrator. By creating two parallel slits with twin hairs, razor blades or pencil leads, you'll record textbook interference fringes, determine the laser wavelength to within a few percent (tens of nm), and master the calculations that appear in every H2 Physics paper - no optics bench needed.

Keep this drill in your Paper 4 toolkit via our H2 Physics Experiments hub.

1 Why Young's Double Slit Changed Physics Forever

In 1801 Thomas Young showed that two coherent slits create an interference pattern impossible to explain with classical particles. Reproducing it today lets you:

Visualise superposition and path difference
Touch the foundations of quantum mechanics
See why Blu-ray beats DVD (shorter $\lambda$ gives closer data tracks)
Measure distances down to hundreds of nanometres with a ruler and some string

And the kit fits in a pencil case.

2 Creating Your Double Slits - Three DIY Methods

Method

Materials

Typical slit separation

d

Build outline

Step	Action
1	Mark the central bright fringe ( $n=0$ ).
2	Count, say, five bright fringes to the right ( $\Delta n = 5$ ).
3	Measure total distance $\Delta \ell$ between those two maxima.
4	Fringe spacing $x\space=\space\Delta \ell\space/\space\Delta n$ .

Quantity	Typical value	Instrument limit	% uncertainty
Slit separation $d$	0.150 mm	±0.010 mm (calipers)	±6 %
Screen distance $D$	3.00 m	±0.005 m (tape)	±0.2 %
Fringe spacing $x$	13.0 mm	±0.5 mm (ruler)	±4 %

Symptom	Likely cause	Remedy
No fringes	Laser hits only one gap or gaps misaligned	Block each slit in turn to check; realign
Fringes curved	Screen not parallel to slits	Square up screen
Fringes too close	Gap $d$ too large	Use thinner shim or longer $D$
Missing every second fringe	Slit width $a$ too large	Narrow the slits or widen $d$

DIY Young's Double Slit with Laser Pointers: Wave Nature of Light for H2 Physics

1 Why Young's Double Slit Changed Physics Forever

2 Creating Your Double Slits - Three DIY Methods

3 Laser Selection and Safety

4 Experimental Setup

5 What You'll See

6 Measuring Fringe Spacing

7 Calculations

8 Uncertainty Analysis

9 Advanced Investigations (All Start With a Two-Slit)

10 Common Problems and Fixes

11 Link to Quantum Weirdness

12 Success Checklist

References

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