Newton used a corpuscular theory of light to explain reflection - AQA - A-Level Physics - Question 2 - 2019 - Paper 7

To evaluate the rejection of Newton's corpuscular theory in favor of Huygens' wave theory, it's essential to explore how each theory explains refraction:

1. Explanation of Refraction:

   • Newton's corpuscular theory posits that light consists of small particles, called corpuscles, which travel in straight lines and change direction when encountering different media. However, this model fails to explain several observable phenomena, such as diffraction.
   • Huygens' wave theory describes light as a wave that expands spherically, generating wavefronts that travel through different mediums at varying speeds, providing a more comprehensive framework to explain bending and spreading of light during refraction.

2. Experimental Evidence Supporting Huygens' Theory:

   • Experiments demonstrating the wave nature of light, such as Young's double-slit experiment, provide clear evidence of interference patterns that cannot be accounted for by corpuscular theory. These results illustrate the wave properties of light, thus promoting the acceptance of Huygens’ theory over Newton's.
   • Additionally, the study of refraction at various interfaces showed that light bends consistently according to the wave speed ratios in different media, aligning with Huygens’ approach.

Therefore, the corpuscular model was gradually set aside as the wave theory provided a more robust understanding of optical phenomena.

A plane-polarised electromagnetic wave travels through a vacuum in a uniform direction with its electric and magnetic fields oscillating perpendicular to each other and to the direction of wave propagation.

• Diagram: A labelled diagram would illustrate the direction of propagation, with arrows indicating the oscillations of the electric field (E-field) and the magnetic field (B-field).

• Key Features:

  • The electric field vibrates in one plane, while the magnetic field vibrates in a plane that is perpendicular to the electric field.
  • These waves have a constant amplitude and frequency.
  • The energy of the wave is carried in the direction of propagation with a speed equal to the speed of light in a vacuum, denoted as c, where: $c = 3 imes 10^8 ext{ m/s}$ .

In summary, a plane-polarised electromagnetic wave can be visually represented as two perpendicular oscillating fields (E and B) moving through space in a direction perpendicular to both fields.