Katarina Susman

How to Teach Liquid Crystals

We present a teaching unit on liquid crystals. The unit has already been implemented into the university undergraduate pedagogical study programs for future teachers of Physics and Chemistry, preschool teachers and teachers at the lower grade of the elementary school at Faculty of Education, University of Ljubljana. The unit develops students’ knowledge on the existence of more than three phases of matter and the existence and properties of anisotropic materials, focusing on the biaxiality and birefringence. The unit is multidisciplinary since students perform the experiments with the MBBA nematic liquid crystal which they synthesize themselves. Our final goal is to implement the teaching unit to the high school curriculum (for students 14–18 years old).

Experimental demonstration of longitudinal magnification

We describe an experiment which enables the observation of longitudinal magnification for the real image of a three-dimensional (3D) object formed by a converging lens. The experiment also shows the absence of longitudinal inversion. Possible reasons for misconceptions with respect to real images and longitudinal inversions are discussed and a teaching sequence to suppress them is suggested. As an illustration, an experiment clearly showing the presence of longitudinal inversion for the real image of a 3D object formed by a concave mirror is also described.

A Mechanical Model for Phase Transitions in Smectics

A mechanical model is a simple device made out of helical springs. Using the mechanical model one can visualize the difference between the first and the second order phase transitions. The analogy between the mechanical model and phase transitions in liquid crystals will be discussed. The parameters of the simple device (length, frequency, amplitude, tilt, etc.) can serve as an analogy for the parameters used in theories of phase transitions. The simple mechanical model is also convenient for the presentation and visualization of the dynamics near SmA-SmC phase transition in liquid crystals.

Teaching Liquid Crystals with a Wood Model

The uniaxial symmetry in the liquid crystalline phase leads to anisotropy in many physical properties. A simple look on a piece of wood reveals that also its structure is anisotropic. It has also strong anisotropic dielectric properties in the microwave range, like liquid crystals in the visible range. Therefore the wood can serve as a model for demonstration of anisotropic optical properties in liquid crystals. Experiments for more illustrative explanation of the anisotropic properties are presented. As wood is transparent for microwaves, many anisotropic properties can be illustrated experimentally, using a simple school microwave kit.

Water transport in trees—an artificial laboratory tree

Water transport in tall trees is an everyday phenomenon, seldom noticed and not completely understood even by scientists. As a topic of current research in plant physiology it has several advantages for presentation within school physics lectures: it is interdisciplinary and clearly shows the connection between physics and biology; the construction of an artificial tree is an ideal laboratory project, which enables detailed studies of several phenomena related to water transport in an artificial tree model; it also clearly shows the failures of widespread ideas about the origins of the upward water flow. We present the construction of the laboratory tree, suggest measurements that illustrate water transport and present a few additional experiments which clearly show why water transport in trees higher than 10 m is still an ongoing debate amongst plant physiologists.

Can the Full Moon and the Sun Be Observed on the Same Side of the Sky

An ordinary flight became an interesting and amusing event when a look through the window of the plane revealed unusual light spots on the winglet. This article discusses the occurance we saw. Two possible explanations are presented.

Is the General Angle Between the Tilt and the Polarization Possible in Rod-Like Systems?

Smectic structures with general orientation of polarizations with respect to the tilt are known from systems formed of bent-shaped molecules. However, such structures may exist in distorted clock systems of SmCFI1 and SmCFI2 phases in antiferroelectric liquid crystals formed of rod-like molecules. We present the analysis of circumstances in which the general angle between the polarization in the tilt is possible.

Theoretical Explanation of the Continuous Pitch Evolution

In this contribution we present the theoretical explanation of continuous INHP pitch evolution in SmC*α using the phenomenological discrete model of antiferroelectric liquid crystals. In this model there are many phenomenological coefficients which were extracted from the resonant x-ray diffraction measurements. The procedure of extraction of coefficients is described to detail.