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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 horizon... 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
When corpuscles reflect off a surface, the horizontal component of their velocity remains Unchanged, while the vertical component of their velocity is Changed. This is due to the reflection causing an inversion in the direction of vertical motion, while horizontal motion continues in the same direction.
Step 2
Discuss the evidence that led to the rejection of Newton's corpuscular theory.
Answer
Newton's corpuscular theory was challenged due to several key pieces of evidence supporting the wave theory:
1. Wave Fronts and Diffraction
Huygens' principle demonstrated that light behaves as a wavefront, where each point on a wavefront serves as the source of new wavelets. This explains phenomena like diffraction, which cannot be adequately described by corpuscular theory.
2. Interference Patterns
Experiments such as Young's double-slit experiment illustrated that light creates interference patterns, which are a hallmark of wave behavior, contradicting the notion of particles traveling independently.
3. Polarization of Light
The existence of polarized light and its behavior could not be satisfactorily explained by Newon's corpuscular theory, but aligns well with wave theory that describes oscillations in specific planes.
Conclusion
The accumulation of such evidence led the scientific community to favor Huygens' wave theory over Newton's corpuscular approach due to its ability to explain a broader range of optical phenomena.
Step 3
Describe a plane-polarised electromagnetic wave travelling through a vacuum.
Answer
A plane-polarised electromagnetic wave consists of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.
Key Characteristics:
- Direction of Propagation: The wave travels in a straight line in a vacuum.
- Electric Field (E): The electric field oscillates in a single direction (the plane of polarization).
- Magnetic Field (B): The magnetic field also oscillates perpendicular to the electric field and the direction of propagation.
Diagram:
- You may represent this with a diagram where the wave travels to the right, the electric field oscillates up and down, and the magnetic field oscillates out of the page (or left and right). This diagram effectively illustrates the nature of the plane-polarised wave.