Experiences

Learning by doing

Cristina Smirnov

Romania

High Secondary School

Chemistry

Laboratory

Direct

Students usually have difficulties because they find science too abstract. It is true that science uses a wide range of abstract terms and deals with lots of abstract concepts that are not part of everyday conversation. That is why we have to introduce them gradually in a simple way through experiments in most cases. I usually stir my students’ curiosity and start with a lot of questions, which is good food for thought. They know that they will be involved in exciting experiments, which will help them find answers. Learning by doing is a successful way to decode science. The following experiment intrigued my students first and then it was carried out for those who didn’t know it until it became the most popular activity among all students, or rather most of them. It started with a trick they saw once: it was about a message written on a board which was not visible when the light was on but became visible when the light was off. That is how I introduced the concept of black light. The reason black lights are called "black lights" is because they give off very little light that our eyes can see. Visible light contains a spectrum of colors ranging from red, orange, yellow, etc. Beyond violet light in the spectrum is ultraviolet light, which our eyes cannot detect. After this explanation we did the following experiment: we needed: a black light, petroleum jelly and a piece of paper. I asked one of the students to dip his fingers into the jelly, then use his finger to write a short message on the piece of paper. The message was not visible. When he has finished, we turned off the room lights and turned on the black light. The message became visible in the black light. The explanation was simple and everybody understood it. Most of the time when we look at an object, we see light reflected from the surface of the object. But with a black light, there isn't much visible light, so simple reflection of light doesn't account for how bright the jelly glows. Petroleum jelly contains substances called phosphors. A phosphor absorbs radiation and emits it as visible light. So the phosphors in the jelly are absorbing the invisible ultraviolet radiation from the black light and emitting visible light.