We report on the competition problems given at the 39th International Physics Olympiad held in Hanoi, Vietnam, which consist of three theoretical and one experimental problems. The abbreviated solutions are presented. The distribution of marks for the problems is also shown. (Contains 2 tables and 8 figures.)

On Earth, using ordinary visible light, one can create a single image of light recorded over time. Of course a movie or video is light recorded over time, but it is a series of instantaneous snapshots, rather than light and time both recorded on the same medium. A pinhole camera, which is simple to make out of ordinary materials and using ordinary…

Two curious thought experiments concerning the speed of light are presented which have been used to provoke the interest of undergraduate physics students. (Contains 2 figures.)

The familiar kaleidoscope toy was developed by the Scottish physicist David Brewster (1781-1868) in 1816, patented by him in 1817, and described in his 1819 book, "A Treatise on the Kaleidoscope." Generations of elementary students have made their own kaleidoscopes by assembling three microscope slides inside a tube and looking through it at a…

The wave nature of light is not part of students' common experiences, so often physics teachers and textbooks will add a historical anecdote about how scientists, too, were tricked by light. A common one is how, in the early 19th century, Poisson declared that since Fresnel's ideas on the wave nature of light implied that the shadow cast by a disk…

You may have observed that a small goldfish swimming in a spherical fishbowl can suddenly disappear. Why does this happen? The effect is due to total internal reflection. In this paper we find the locations of the fish and the observer's eye for which the fish cannot be seen.

An activity has been designed for the purpose of teaching how light is dispersed in a straight line and about the interaction between matter and light as well as the related concepts of shadows, partial shadows, reflection, refraction, primary colours and complementary (secondary) colours, and differentiating the relationship between colours, all…

The purpose of this study was to analyze participants' levels of hemoglobin as they performed arithmetic mental calculations using Optical Topography (OT, helmet type brain-scanning system, also known as Functional Near-Infrared Spectroscopy or fNIRS). A central issue in cognitive neuroscience involves the study of how the human brain encodes and…

In Japan, junior high school students learn about energy conversion between kinetic and potential energy. In addition, they learn about energy conversion among different kinds of energy, such as mechanical, electrical, thermal, light and chemical. As for the conversion between electrical and light energy, teachers usually use lamps or LEDs to…

This research was intended to investigate whether Turkish students who had graduated from high school used the wave theory of light properly in explaining optical phenomena. The survey method was used in this research. The data, which were collected from 175 first year university students in Turkey, were analysed quantitatively and qualitatively.…

Nanoscience and nanotechnology currently represent one of the most rapidly developing fields of science and technology; therefore, the fundamental principles of nanoscience and nanotechnology should be understood by college and even high school students as well as by members of scientific communities. Silver, as the pioneer material in these…

When the subject of buildings and daylighting arises, most people's thoughts will turn first to windows. To the uninitiated, it seems a simple formula: more windows, more daylight; fewer windows, less daylight. But designers know that effective use of daylighting in a building design involves more than just letting in light to otherwise darkened…

Diffusion is a fundamental phenomenon that is vital in many chemical processes such as mass transport in living cells, corrosion, and separations. We describe a simple undergraduate-level experiment based on Weiner's Method to probe diffusion in a ternary aqueous mixture of small molecular-weight molecules. As an illustration, the experiment…

Three plain mirrors, perpendicular to each other, reflect a beam of light back into the direction it came from. An activity is suggested where pupils can employ this feature of perpendicular mirrors and make their own corner cube retroreflector--a kind of cat's eye. (Contains 7 figures and 1 footnote.)

This paper shows a child psychotherapist learning and developing her technique as she attempts to make contact with a child who is extremely hard to reach. It is based on the first two years of three-times-weekly intensive psychotherapy of a latency girl who had little faith in a helpful therapeutic relationship. Her defences against such a…