The Design of Media on Two-Lens System Experiment ( MTLSE ) for Pre-service Physics Teachers

This article is a part of the research in designing a model of the geometrical-optics game on optics' courses for pre-service physics teachers (PPTs). This article describes the preliminary form of product, the result of validation, and PPTs’ responses to the media on two-lens system experiment (MTLSE). The validation of this media has been done according to physics subject matter, instructional media and pedagogical experts. The implementation of MTLSE using the one-shot case study design involving 25 PPTs at one of the Islamic universities in Bandung. We collected the data of MTLSE validation and PPTs’ responses through non-test techniques with questionnaire instruments. The data using quantitative descriptive analysis technique. The results of MTLSE validation can be good categorized. Besides, generally, the PPTs’ responses are good categorized toward the implementation of MTLSE on optics' courses.


INTRODUCTION
Optics is a branch of physics that deals with the behavior and characteristics of light and other electromagnetic waves (Young & Freedman 2003).Geometrical optics is one branch of optics that discusses light based on the propagating properties of light that traveling in straight lines, explaining the reflection and refraction of light, and being the foundation for making the optical equipment (Saprudin 2018).The term geometrical optics appears as a result of the critical role of geometry in analyzing how the formation of images when the light rays reflected by a mirror and refracted through lenses (Young & Freedman 2003).
The two-lens system is part of the geometrical optics learning material that is found to still have low competency achievement (Saprudin, Liliasari, & Prihatmanto 2017).The results of concept analysis show that in general, the concepts in the geometrical optics learning material are dominated by concrete concept labels that are defined from real optical phenomena are easily found in everyday life applications (Saprudin 2018).However, the results of observations at the location of the study showed that the limitations of the physics experiment tools became one of the factors that caused the two-lens system experiment not to be carried out.It creates the pre-service physics teachers (PPTs) at the research location to have difficulty in understanding the concepts in this material.The researchers have shown that in its implementation, the teaching and learning process of optics material that has been carried out is dominated by the application of various approaches, models, or methods of learning, and the use of various instructional media ranging from traditional media to the more sophisticated media.This geometrical-optics learning activity is inseparable from hands-on activities that are carried out in real physical activities or through the assistance of virtual media.
As a first step in designing geometrical-optics games aimed for PPTs, researchers consider it necessary to create a media and experimental procedures that can provide learning experiences related to the concept of the two-lens system.Besides, this study describes the results of validation and PPTs' responses to the implementation of media on two-lens system experiment (MTLSE) in the optics course.

RESEARCH METHODOLOGY
This research conduct in a pre-experimental design with a one-shot case study design.In this research, one subject group namely 25 PPTs in one of the Islamic Universities in Bandung was subject to treatment in the form of lectures using the MTLSE, then after that, measurements were done regarding the PPTs' responses to the implementation of MTLSE in the courses.Before being used, MTLSE is validated in advance both from the material aspects of physics, instructional media, and pedagogics.
The subject of validation involved two physics material experts, two instructional media experts, and two pedagogical experts.The data related to MTLSE validation collected through non-test e-Jurnal: http://doi.org/10.21009/1techniques with validation sheet instruments which packaged in the form of a questionnaire with closed-ended questions.The data associated with PPTs' responses to the implementation of MTLSE in lectures collected through the questionnaires.The data analysis techniques were carried out using quantitative descriptive analysis techniques.

RESULTS AND DISCUSSION
The Design of Media on Two-Lens System Experiment (MTLSE) The central principle of MTLSE is to find various combinations of lenses at a certain distance that can produce the sharpest image under certain conditions.Multiple combinations of lenses with a certain distance between lenses found through experiments will be analyzed and compared with the results of mathematical calculations.The PPTs will also be required to think creatively in finding possible lens combinations, and also required to think critically in analyzing and comparing the data from experiments with mathematical calculation results.
The apparatus used in designing this MTLSE include; Econo curtain rails, 12mm plywood, 3mm thin plywood, 12mm aluminum clips, 12mm bolts, biconvex lenses (f = +50 mm, +100 mm, +150 mm, +200 mm and +250 mm), biconcave lens (f = -50 mm, -100 mm, -150 mm, -200 mm and -250 mm), arrow diaphragm, white screen, lens holder, screen holder, arrow diaphragm holder, measuring tape, LED lights source (MR16, 4.5W) and LED spotlight.The MTLSE design shown in FIGURE 1.   Overall, the results of MTLSE validation according to the physics matter experts are categorized as good (75%), according to the instructional media experts are classified as good (74%), and according to the pedagogical experts are classified as good (73%).Based on that, MTLSE can be declared as feasible for use in the optical course.

PPTs' Responses toward The Implementation of MTLSE
PPTs' responses are focused on two target focuses namely; 1) PPTs' responses toward MTLSE and 2) PPTs' responses toward two-lens system experiment design.Overall, PPTs gave good responses to the MTLSE and also to the two-lens system experiment design.It is indicated by the total score of 1415 from a maximum score of 1800.The results of the questionnaire suggest that this experimental design is considered as something new for PPTs at the research location.

CONCLUSION
The main principle of MTLSE is finding various combinations of lenses at a certain distance that can produce the sharpest image under certain conditions.Different lens combinations that found through experiment will be analyzed and compared with the results of mathematical calculations.Some of the advantages of MTLSE that have been designed include; a) easy to operate, b) the image that formed by two-lens system can be clearly observed on the screen, c) shifting the components of MTLSE (the object distance, image distance, and the distance between two lenses) are easy to do, and d) using LED light source so do not disturb the eyes during observation.
The results of MTLSE validation according to physics material, instructional media and pedagogical experts can be categorized as good.Besides, PPTs' responses to the implementation of MTLSE are categorized as good.The products and experiment designs produced will be used to design a geometrical-optics game model that can be used in optics course for PPTs.

FIGURE 1 .
FIGURE 1.The Display of Media on Two-Lens System Experiment (MTLSE); (a) front view, (b) side view

TABLE 1 ,
Results of MTLSE Validation by Physics Material Experts Results of MTLSE Validation by Instructional Media Experts TABLE 2, andTABLE 3 show the results of validation by physics matter, instructional media, and pedagogical experts.TABEL 1. e-Jurnal: http://doi.org/10.21009/1TABEL 2.
TABLE 4 and TABLE 5 show the PPTs' responses.

TABLE 4 .
PPTs' Response to MTLSE and Experimental Design of Two-Lens Systems