Onion Diffraction Article


I recently had an article published in the Physics Teacher, a peer-reviewed journal of the American Association of Physics Teachers. The article describes an experiment to estimate the size of onion epidermal cells by studying the diffraction patterns that are formed (like the one above) when laser light passes through the cells. Below is an abstract.

Estimating the Size of Onion Epidermal Cells from Diffraction Patterns

Bioscience and premedical profession students are a major demographic served by introductory physics courses at many colleges and universities. Exposing these students to biological applications of physical principles will help them to appreciate physics as a useful tool for their future professions. Here I describe an experiment suitable for introductory physics where principles of wave optics are applied to probe the size of onion epidermal cells. The epidermis tissue is composed of cells of relatively uniform size and shape so the tissue acts like a one-dimensional transmission diffraction grating. The diffraction patterns generated when a laser beam passes through the tissue are analyzed and an estimate of the average width of individual onion epidermal cells is calculated. The results are compared to direct measurements taken using a light microscope. The use of microscopes and plant-cell tissue slides creates opportunities for cross-discipline collaboration between physics and biology instructors.