A laser is used in a supermarket barcode scanner to read the barcodes on products. Explain why laser light is well suited to this application, referring to the properties of laser light in your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Barcode scanners in supermarkets work by shining light onto a barcode and detecting the pattern of reflected light. The scanner must read the barcode accurately from a short distance away.
Model answer (5 marks)
Laser light is monochromatic, so it has a single wavelength that can be detected against background light.
Laser light is coherent, meaning the waves are in phase and produce a stable interference pattern.
Laser light is collimated, forming a narrow, parallel beam that does not spread.
The narrow beam can be aimed precisely at the small bars of the barcode.
Because the wavelength is consistent, the detector can reliably distinguish the reflected light from ambient light, giving a clear signal.
Laser light is coherent, meaning the waves are in phase and produce a stable interference pattern.
Laser light is collimated, forming a narrow, parallel beam that does not spread.
The narrow beam can be aimed precisely at the small bars of the barcode.
Because the wavelength is consistent, the detector can reliably distinguish the reflected light from ambient light, giving a clear signal.
Examiner tips
- Mention monochromatic, coherent, collimated properties in separate sentences.
- Explain how each property benefits barcode reading.
- Use terms like ‘single wavelength’, ‘in phase’, ‘parallel beam’.
- Keep answer concise, 5 points total.
Common mistakes
- Confusing laser light with any light source; not stating monochromatic. Failing to mention coherence or collimation. Using vague terms like ‘bright’ or ‘focused’ without technical detail.
Mark scheme (5 marks)
- Laser light is monochromatic (single wavelength / single colour / single frequency)
- Laser light is coherent (waves are in phase with each other)
- Laser light is collimated / forms a narrow, parallel beam that does not spread out
- The narrow beam allows it to be aimed precisely at the small bars of the barcode
- The consistent / single wavelength means the detector can reliably distinguish reflected light from background light, giving a clear signal
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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