# KS5 Optics

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# Wave Properties & Optics - Objectives

Content

• Refraction of light

• Total internal reflection

• Interference

• Diffraction

• Two-source interference

Learning Outcomes

• Refractive index of a substance s , ns = c/cs; Candidates are not expected to recall methods for determining refractive indices
• The refractive index of air being approximately 1
• Snell's Law of refraction for a boundary between two different substances of refractive indices n1 and n2 in the form:
n1sin θ1 = n2sin θ2

• Total internal reflection including calculations of the critical angle θc at a boundary between a substance of refractive index n1 and a substance of lesser refractive index n2 or air:
sin θc = n2/ n1
• Simple treatment of fibre optics including function of the cladding with lower refractive index around central core limited to step index only; application to communications.
• Material and modal dispersion
• the principles and consequences of pulse broadening and absorption
• Appearance of the diffraction pattern from a single slit using monochomatic and white light
• the qualitative treatment of the variation of the width of the central diffraction maximum with the wavelength and slit width (intesity-angular separation graph is not required)
• The plane transmission diffraction grating at normal incidence; optical details of the spectrometer will not be required
• Derivation of d sin θ = nλ, where n is the order number
• Applications; e.g. to spectral analysis of light from stars
• The concept of path difference and coherence
• The laser as a source of coherent monochromatic light used to demonstrate interference and diffraction; comparison with non-laser light; awareness of safety issues. Candidates will not be required to describe how a laser works.
• Young's double-slit experiment: the use of two coherent sources or the use of a single source with double slits to produce an interference pattern
• The appearance of the interference fringes produced by a double slit system, fringe spacing, w = λD/s , where s is the slit separation.
• the production of an interference pattern using white light
• how to describe and explain interference produced with sound and electromagnetic waves
• how the understanding of the nature of electromagnetic radiation has changed over time
• REQUIRED PRACTICAL - investigation of interference effects to include the Young's double-slit experiment and interference by a diffraction grating