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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
According to the corpuscular theory, when corpuscles are reflected, their horizontal component of velocity remains unchanged, while the vertical component changes direction. Thus, 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
Huygens' wave theory provided a more comprehensive explanation of light behavior, particularly in phenomena such as refraction and interference. Key points include:
Comparison of Theories
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Refraction Explanation:
- Newton's corpuscular theory struggled to explain refraction at interfaces; it proposed particles that would not bend but merely change speed.
- Huygens' wave theory illustrated that wavefronts could bend when entering a medium of different density, thus explaining refraction more accurately.
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Interference and Diffraction:
- Experiments showed light could create patterns of interference, which could not be adequately explained by a corpuscular view. Huygens' framework accommodated these behaviors as waves interact constructively and destructively.
Experimental Evidence
- Acceptance of Wave Theory:
- Factors such as Young's double-slit experiment demonstrated wave properties of light, providing clear evidence for the wave theory.
- The measurement of light speed in different media confirmed the predictions made by the wave theory, bolstering its acceptance over Newton’s corpuscular approach.
Step 3
Describe a plane-polarised electromagnetic wave travelling through a vacuum.
Answer
A plane-polarised electromagnetic wave is characterized by oscillating electric and magnetic fields that are oriented in a specific direction. The key attributes include:
Attributes of the Wave
- Electric Field (E): Oscillates in a single plane, perpendicular to the direction of wave propagation.
- Magnetic Field (B): Also oscillates in a plane, perpendicular to both the electric field and the direction of wave travel.
Diagram (optional)
To illustrate:
- A labelled diagram could depict the electric field oscillating vertically and the magnetic field oscillating horizontally, with the wave propagating in a diagonal direction.
This diagram would highlight the perpendicular relationships of the fields and their uniform oscillations in the vacuum.