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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 the velocity of the corpuscles remains Unchanged, while the vertical component of the velocity becomes Changed upon reflection.
Step 2
Discuss the evidence that led to the rejection of Newton's corpuscular theory.
Answer
Newton's corpuscular theory was rejected due to several pieces of experimental evidence.
Comparing Refraction Explanations
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Newton's Corpuscular Theory:
- Proposed that light consists of particles (corpuscles) which travel in straight lines.
- This theory struggled to explain the phenomenon of interference and diffraction observed in experiments.
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Huygens' Wave Theory:
- Explained that light behaves as a wave, allowing it to exhibit both reflection and refraction through wavefronts.
- Huygens' principle effectively demonstrated how light could bend as it passes from one medium to another.
Experimental Evidence
- Young’s Double-Slit Experiment: Showed that light produces interference patterns, a phenomenon that cannot be explained by the corpuscular theory as particles would not create such patterns.
- Observation of Total Internal Reflection: Occurs in certain mediums indicating wave behavior, which involves the bending of waves rather than particles.
Acceptance of Wave Theory
The cumulative experimental results supported Huygens' wave theory, leading to the broader acceptance of the concept that light behaves as a wave.
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.
Characteristics
- Direction of Propagation: The wave travels in a straight line, described by the direction of energy transfer.
- Electric Field (E): Oscillates in a single plane, making it polarised. The magnitude of the electric field typically varies sinusoidally over time.
- Magnetic Field (B): Oscillates at right angles to the electric field and also in a plane perpendicular to the direction of wave travel.
Diagram (suggested)**:
- Include a diagram showing the direction of propagation, and the planes of the electric and magnetic fields.