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Newton used a corpuscular theory of light to explain reflection - AQA - A-Level Physics - Question 2 - 2019 - Paper 7
Question 2
Newton used a corpuscular theory of light to explain reflection. Figure 2 shows how corpuscles would reflect from a horizontal surface. What happens to the horizont... show full transcript
Worked Solution & Example Answer:Newton used a corpuscular theory of light to explain reflection - AQA - A-Level Physics - Question 2 - 2019 - Paper 7
Step 1
What happens to the horizontal and vertical components of the velocity of the corpuscles, according to the theory, when they are reflected?
Answer
The horizontal component of velocity remains unchanged while the vertical component changes. Therefore, the correct box to tick is:
- Horizontal component of velocity: Unchanged
- Vertical component of velocity: Changed
Step 2
Discuss the evidence that led to the rejection of Newton's corpuscular theory.
Answer
Newton's corpuscular theory of light suggested that light travels in particles. However, several pieces of evidence led to its rejection:
Refraction
Huygens' wave theory explained refraction through the concept of wavefronts, where the change in speed of light at the interface causes bending. This was supported by Snell's Law, which describes how the angle of incidence relates to the angle of refraction. The corpuscular theory could not adequately explain these observations.
Interference and Diffraction
Experiments demonstrating interference patterns (such as Young's Double Slit Experiment) provided strong evidence for the wave nature of light. Newton's theory failed to account for such phenomena, which were consistently observed with waves.
Polarization
Light behaving as a wave can be polarized, which was again unexplainable by the corpuscular theory. The observations of polarized light indicate that light consists of transverse waves.
Step 3
Describe a plane-polarised electromagnetic wave travelling through a vacuum.
Answer
A plane-polarised electromagnetic wave travels through a vacuum with electric and magnetic fields oscillating perpendicular to each other and the direction of propagation. Presenting a labelled diagram would enhance understanding:
- The electric field vector (E) oscillates in one plane.
- The magnetic field vector (B) oscillates in a plane perpendicular to E.
- Both fields are perpendicular to the direction of travel of the wave (represented as the z-axis).
The oscillations can be described mathematically using sinusoidal functions.