A laser is used in a concert to project patterns and beams of light across a large arena. The laser beam travels a long distance without spreading out, and all the light is the same colour. Explain why laser light is well-suited to this application, referring to the properties of laser light.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In large arenas, lighting designers use lasers rather than ordinary spotlights to create long-distance light effects. The beams remain narrow even when they travel tens of metres across the venue.
Model answer (5 marks)
Laser light is coherent, so the waves are in phase and the beam remains narrow over long distances.
Laser light is monochromatic, meaning all photons have the same wavelength and therefore the same colour.
Laser light is highly collimated, producing a very narrow, parallel beam.
Because the beam does not spread out, it can travel tens of metres across the arena and still be seen as a distinct narrow beam.
Because the light is monochromatic, the beam appears as a single, pure colour, giving a sharp, vivid pattern without a spectrum.
Laser light is monochromatic, meaning all photons have the same wavelength and therefore the same colour.
Laser light is highly collimated, producing a very narrow, parallel beam.
Because the beam does not spread out, it can travel tens of metres across the arena and still be seen as a distinct narrow beam.
Because the light is monochromatic, the beam appears as a single, pure colour, giving a sharp, vivid pattern without a spectrum.
Examiner tips
- Use the exact terms – coherent, monochromatic, collimated. Show the link between coherence and lack of spreading. Mention the pure colour gives sharp patterns.
- Include all five points in a logical order.
Common mistakes
- Confusing coherence with monochromaticity. Forgetting to mention the beam’s narrowness or the pure colour effect.
Mark scheme (5 marks)
- Laser light is coherent / the waves are in phase with each other
- Laser light is monochromatic / all one wavelength / all one colour / single frequency
- Laser light is highly collimated / forms a very narrow parallel beam
- Because the beam does not spread out, it can travel a large distance across the arena and still be seen as a distinct narrow beam
- Because the light is monochromatic, the beam appears as a single, pure colour which produces a sharp, vivid pattern / is not split into a spectrum
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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