Newton's & Huygen's Theories of Light
Physics: AQA A Level, topic 12.2.1
Huygen's Wave Theory
Huygen believed that light traveled as a wave.
Huygen's wave theory
- Huygen’s agreed with other scientists that light existed as a wave.
- He developed a general model of waves known as Huygen’s principle.
Huygen's principle
- Every point on a wavefront is itself a source of secondary wavelets.
- Each wavelet will spread out as a new wave at a point source.
- A new wavefront propagates as a tangent to the old wavefront.
Impacts of Huygen's theory
- Huygen’s theory explained:
- Reflection.
- Refraction.
- Diffraction.
- There was currently no evidence of diffraction, and so there was some doubt about his theory.
Newton’s Corpuscular Theory of Light
Newton's corpuscular theory was preferred to Huygens' wave theory.
Newton's corpuscular theory
- Newton believed that light was made of small particles called corpuscles.
- His theory relied heavily on his widely accepted theories of motion.
Newton's evidence
- Newton believed his theory because light seemed to always travel in straight lines.
- His theory explained reflection as the particle bouncing from the surface.
- His theory explained refraction by saying that particles travel faster in a medium of higher density.
Scientific community
- The scientific community believed Newton’s corpuscular theory over Huygen’s wave theory.
- Newton’s theory was more intuitive.
- Newton had an established reputation.
Young's Double Slit Experiment
Young's double slit experiment provided evidence to support Huygen's wave theory.
Young's double slit experiment
- Young performed an experiment where he shone two coherent light sources through two slits.
- An interference pattern was shown on the screen behind the slits, which suggested that the light was interfering.
Significance of the experiment
- Young’s experiment showed that light could behave as a wave, which gave evidence to support Huygen’s wave theory.
Scientific community
- Huygen’s theory was still not accepted, because of Newton’s reputation within the scientific community.
- After a decade, Young formalised that light was a transverse wave which explains these properties, and the scientific community began to agree.
Test yourself on Newton's & Huygen's Theories of Light
What is the relationship between the new and old wavefronts?
Why did people doubt Huygen's theory?
What did Newton believe that light was made of?
Which theory of light was preferred at the time of its suggestion?
An interference pattern was shown on the screen behind the slits. What did this suggest?