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Lesson: Thin Film Interference Physics • 9th Grade

In this lesson, we will learn how to analyze the interference of light reflected from parallel layers of substances with different refractive indices.

Lesson Plan

Students will be able to

  • diagrammatically describe the mechanism of production of thin film interference,
  • for a thin film of refractive index 𝑛 that is resting on a substance of greater refractive index than 𝑛, relate the separation, 𝑑, between the upper and lower layers of the thin film to the order, π‘š, of the interference maximum produced by light that has wavelength πœ† in a vacuum when it reflects from the upper and lower layers of the thin film, using the equation 2π‘‘πœƒ=π‘šπœ†π‘›cos, where πœƒ is the angle of incidence at the upper layer,
  • for a thin film of refractive index 𝑛 that is resting on a substance of greater refractive index than 𝑛, relate the separation, 𝑑, between the upper and lower layers of the thin film to the order, π‘š, of the interference minimum produced by light that has wavelength πœ† in a vacuum when it reflects from the upper and lower layers of the thin film, using the equation 2π‘‘πœƒ=ο€»π‘šβˆ’ο‡πœ†π‘›cos, where πœƒ is the angle of incidence at the upper layer,
  • for a thin film of refractive index 𝑛 that is resting on a substance of smaller refractive index than 𝑛, relate the separation, 𝑑, between the upper and lower layers of the thin film to the order, π‘š, of the interference maximum produced by light that has wavelength πœ† in a vacuum when it reflects from the upper and lower layers of the thin film, using the equation 2π‘‘πœƒ=ο€»π‘šβˆ’ο‡πœ†π‘›cos, where πœƒ is the angle of incidence at the upper layer,
  • for a thin film of refractive index 𝑛 that is resting on a substance of smaller refractive index than 𝑛, relate the separation, 𝑑, between the upper and lower layers of the thin film to the order, π‘š, of the interference minimum produced by light that has wavelength πœ† in a vacuum when it reflects from the upper and lower layers of the thin film, using the equation 2π‘‘πœƒ=π‘šπœ†π‘›cos, where πœƒ is the angle of incidence at the upper layer,
  • relate the thickness, 𝑑, of antireflection coating of refractive index 𝑛 to the wavelength, πœ†, in a vacuum of light that the coating prevents reflection of, using the formula 𝑑=πœ†4𝑛.

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