Describe the properties of laser light that make it suitable for use in eye surgery, and explain why ordinary white light from a lamp would not be suitable for the same purpose.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Lasers are used in medicine to carry out delicate surgical procedures, including operations on the human eye. The surgeon can direct the laser beam with great precision to a specific point on the eye.
Model answer (5 marks)
Laser light is monochromatic, so all photons have the same wavelength and colour.
Laser light is coherent, meaning the waves are in phase and have a constant phase relationship.
Laser light is collimated, forming a very narrow, parallel beam that does not spread.
These properties allow the beam to be focused onto a very small, precise spot on the eye, delivering high energy to an exact location.
Ordinary white light from a lamp is not monochromatic, not coherent, and spreads in many directions, so it cannot be focused tightly enough and would damage surrounding tissue.
Laser light is coherent, meaning the waves are in phase and have a constant phase relationship.
Laser light is collimated, forming a very narrow, parallel beam that does not spread.
These properties allow the beam to be focused onto a very small, precise spot on the eye, delivering high energy to an exact location.
Ordinary white light from a lamp is not monochromatic, not coherent, and spreads in many directions, so it cannot be focused tightly enough and would damage surrounding tissue.
Examiner tips
- Use the terms monochromatic, coherent, collimated exactly as in the mark scheme.
- Show the link between these properties and the ability to focus the beam.
- Mention the consequence for ordinary white light – lack of focus and potential damage.
- Keep the answer concise – 5 points only.
Common mistakes
- Confusing laser light with any bright light; not stating all three properties.
- Using vague terms like ‘bright’ or ‘sharp’ instead of the specific terminology.
- Failing to explain why ordinary light would damage tissue.
Mark scheme (5 marks)
- Laser light is monochromatic (all one wavelength/colour)
- Laser light is coherent (all waves in phase / same frequency and phase)
- Laser light is collimated / forms a very narrow, parallel beam that does not spread out
- These properties allow the laser beam to be focused onto a very precise, small spot on the eye (high precision / energy delivered to exact location)
- Ordinary white light is not monochromatic / not coherent / spreads out in all directions, so it cannot be focused precisely enough / would damage surrounding tissue
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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