Particle theory of light

1. Rosal Group 1 Particle theory of light

2. Proposed by Sir Isaac Newton Corpuscular Theory Explained in Opticks published in 1704 Observed: reflection, shadows, light travelling in straight lines Light as small compact particles of energy called corpuscles Light is a particle flying through void Particle theory

3. Light travels in straight lines Light can travel through vacuum According to Newton, light can’t be a wave We can hear sound from behind an obstacle, but we don’t see light – light shows no diffraction Can explain reflection , refraction , rectilinear propagation PARTICLE THEORY EVIDENCES Light traveled as a shower of particles e ach proceeding in a straight line

4. Light from a source arrives on a mirror surface as a stream of particles that will bounce away from the smooth surface A huge number of these particles (corpuscles) are involved in a propagating light beam When the corpuscles touch the mirror, they bounce from different points, reversing their order , producing a reversed image Corpuscular theory of reflection Particle theory is stronger in the reflection phenomenon

5. Particles accelerate as they go from air to medium of greater optical density Explained by forces acting on boundaries between different media Corpuscular theory of refraction

6. Rectilinear propagation Higher the speed, lesser the curve of the path Corpuscles travel at high speeds that they travel in straight lines Strong argument against wave theory – how could waves travel in straight lines ? Reflection When light hits a smooth surface, it’s reflected (like steel ball bearings thrown at a smooth steel plate rebound) Elastic particles Arguments presented

7. Refraction Two level surfaces, one higher than another, edges connected by a slope Ball is rolled on the higher surface toward the slope at a given angle Higher surface -> down the slope -> lower surface  speed up Can be compared to light being refracted Light particles accelerate as they go from a medium to a medium of greater optical density In this case, speed of light must be faster in water than in air Arguments presented

8. When light hits a boundary between two media, some refract, some reflect (characteristics of waves ) To defend: when particles reach the surface, they have fits ; some particles “decide” to go into the water while the rest “decide” to bounce off Problems with the theory

9. “Light is never known to follow crooked passages nor to bend into the shadow” – consistent with particle theory Proposes that light particles must always travel in straight lines If particles encounter the edge of a barrier , shadows will be cast Particles unblocked by the barrier will continue the straight line For diffraction, it is good in a macroscopic scale, but not in a microscopic scale When light is passed through a narrow slit, the beam spreads and becomes wider than expected (supports wave theory) Speed of light was proven to be slower in water Problems with the theory

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