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In the 17th century, Isaac Newton proposed a theory to explain some of the properties of light - AQA - A-Level Physics - Question 1 - 2022 - Paper 7
Question 1
In the 17th century, Isaac Newton proposed a theory to explain some of the properties of light. An alternative theory of light was proposed by Christiaan Huygens at ... show full transcript
Worked Solution & Example Answer:In the 17th century, Isaac Newton proposed a theory to explain some of the properties of light - AQA - A-Level Physics - Question 1 - 2022 - Paper 7
Step 1
Explain how this observation supports Newton’s theory of light.
Answer
This observation of two bright white lines on the screen demonstrates Newton's particle theory of light, which posits that light consists of particles (corpuscles) that travel in straight lines. The sharp edges of the bright lines suggest that there is little diffraction occurring, as the particles travel directly from the double slit to the screen without bending around obstacles. Hence, the observation is consistent with Newton's explanation of how light behaves, supporting the idea that it travels in straight lines.
Step 2
Identify the alterations made by the student and explain how the observations in Figure 2 support Huygens’ theory of light.
Answer
The alterations made by the student include changing the light source or adding a filter that produces coherent light, such as monochromatic light, and observing the resulting pattern on the screen, which displays red and dark fringes.
Huygens’ theory states that every point on a wave front can be considered as a source of secondary wavelets. The resulting interference pattern demonstrates this theory as the red fringes indicate areas of constructive interference, while the dark fringes indicate areas of destructive interference. This observation is evidence of the wave-like nature of light, which is a key component of Huygens’ theory.
Step 3
Discuss these differences in appearance.
Answer
Newton’s theory predicts a pattern of sharp bright and dark bands on the screen, while Huygens’ theory predicts a pattern with smoother transitions due to wave interference.
In the setup described by Grimaldi, if both apertures A and B are illuminated, Newton’s theory would suggest that the light behaves like particles, creating distinct shadows. In contrast, Huygens' theory would predict overlapping waves from both apertures leading to gradual shading and interference patterns on the screen, with less distinct shadows and more blending of light and dark regions.