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Year 11 - Science

Light intensity and the inverse square law

Photosynthesis: factors affecting the rate

Unit Summary

This unit explores factors affecting photosynthesis rates and focuses on planning and conducting experiments. It includes selecting techniques, accurate measurements, data analysis, and evaluating methods to improve reliability and suggest further investigations.

Lesson Summary

You will learn to explain why light intensity decreases further from a light source.

Key Notes

  • Light waves spread out as they travel from a light source.
  • Further away from the light source, the same amount of light is spread out over a greater area.
  • This means the light intensity decreases with increasing distance from a light source.
  • Light intensity is inversely proportional to the square of the distance from a light source (inverse square law).

Vocabulary To Learn

  • light intensity: the amount of light reaching a given surface area in a period of time
  • light source: an object that emits light
  • light waves: oscillations/ripples in electric and magnetic fields
  • inversely proportional: variables are inversely proportional when one increases and the other decreases at the same (proportional) rate, e.g. as one variable doubles, the other variable halves
  • inverse square law: light intensity is inversely proportional to the square of the distance from the light source

Common Mistakes To Avoid

  • Many pupils will believe that by halving the distance from a light source, the light intensity will double.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

Light waves spread out as they travel from a light source. Further away from the light source, the same amount of light is spread out over a greater area.

2. Define this scientific word and use it in context. 'light intensity'

the amount of light reaching a given surface area in a period of time. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Many pupils will believe that by halving the distance from a light source, the light intensity will double. Correction: As a result of light travelling in all directions, this aspect needs to be thought of in terms of area (two dimensions). The lesson takes pupils through an example which demonstrates how light intensity is proportional to the square of the distance.

More Lessons In This Unit

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