# A laser is used in a supermarket barcode scanner to read the barcodes on products. Explain why laser light is more suitable for this purpose than light from an ordinary light bulb.

> Eduqas A-Level Physics — 2.8 Lasers · Explain · 5 marks

> Barcode scanners work by shining a beam of light onto the black and white lines of a barcode and detecting the reflected light. The scanner must be able to read the barcode accurately from a small spot on the barcode surface.

## Mark scheme (5 marks)

1. Laser light is monochromatic (a single frequency/wavelength), so the detector can be tuned to respond to exactly that wavelength
2. Laser light is coherent, meaning all the waves are in phase with each other
3. Laser light is collimated / does not spread out, so it remains a narrow beam over a distance
4. The narrow beam means the light hits a very small spot on the barcode, allowing the fine black and white lines to be distinguished accurately
5. Ordinary light bulb light spreads out in all directions / is not collimated, so it would illuminate too large an area to read the barcode reliably

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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