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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 of light, when the corpuscles are reflected, the horizontal component of their velocity remains unchanged while the vertical component changes direction. Therefore, you should tick the box for 'Horizontal component: Unchanged' and 'Vertical component: Changed'.
Step 2
Discuss the evidence that led to the rejection of Newton’s corpuscular theory.
Answer
Newton's corpuscular theory was primarily rejected due to various experimental findings that supported wave theory.
How Each Theory Explains Refraction
- Newton's Corpuscular Theory: It posited that light consists of particles (corpuscles) that travel in straight lines. Refraction is explained as a change in speed when passing between mediums, leading to a change in direction. However, it struggled to explain phenomena such as diffraction.
- Huygens' Wave Theory: Proposed that light behaves as a wave, where every point on a wavefront acts as a source of secondary wavelets. This theory explains refraction more comprehensively by considering the wavefront's bending during changes in speed across different media.
Experimental Evidence Leading to Acceptance of Wave Theory
- Interference Patterns: Experiments such as Young's double-slit experiment demonstrated interference, a phenomenon that cannot be explained satisfactorily by the corpuscular theory.
- Polarization: The ability of light to be polarized further supports wave behavior, as polarization is a property of transverse waves.
- Diffraction: The bending of light around corners also aligns with wave theory and contradicts the idea of particles traveling in straight lines.
Through these observations, the scientific community largely accepted Huygens' wave theory over Newton's corpuscular theory.
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 oscillate in planes perpendicular to each other and to the direction of wave propagation.
Key Features of the Wave:
- Direction of Propagation: The wave travels in a specified direction, say along the z-axis.
- Electric Field (E): Oscillates in one plane, e.g., the x-y plane.
- Magnetic Field (B): Oscillates at right angles to both the electric field and the direction of propagation, meaning it oscillates in a plane perpendicular to that of the electric field.
- Labelled Diagram: A diagram can be drawn to illustrate that the electric field is denoted by an arrow in the x-direction, the magnetic field by an arrow in the y-direction, and the direction of wave propagation indicated by another arrow in the z-direction.