Narrow-Band Invisibility Cloaking: The Vanishing Test Tube Revisited

• Autores: Jerry T. Barretto
• Localización: The Physics Teacher, ISSN 0031-921X, Vol. 61, Nº. 5, 2023, págs. 371-371
• Idioma: inglés
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• Resumen

  • Invisibility has long been a staple in science fiction. The idea of not being seen has enchanted people for centuries. Recent examples in popular literature include H. G. Wells’s The Invisible Man, Wonder Woman’s invisible plane, and the invisibility cloak featured in several Harry Potter books. While advances in optical cloaking1 have improved the likelihood of realizing invisibility, classroom demonstrations involving a vanishing object immersed in a liquid2–5 have been popular with students and teachers alike. In these demonstrations, the refractive indices of the materials and liquid are very close, and the invisibility effect is observed using white light or a broadband light source. However, since the index of refraction is a function of wavelength,6 any dependence of invisibility on wavelength would not be observed.

    This work revisits the popular demonstration of vanishing objects immersed in a liquid2–5 but keeping in mind that refractive indices are defined at a given wavelength. To determine any effect on invisibility due to different wavelengths, the immersed object is observed through colored filters. This modification may be useful when starting a lesson on Snell’s law or a unit on refraction and helps reinforce the notion that while white light refracts, the constituent wavelengths refract but by different amounts.