Development of the Wimshurst Machine as a Learning Media on Static Electricity Material for Junior High Schools

This research aims to produce a learning media development product in the form of a Wimhurst machine teaching aid that can be used by teachers and students in the physics learning process. This media is expected to improve the knowledge and scientific thinking skills of grade 8 junior high school students in physics lessons on static electricity. This research was conducted in March-June 2014 at the Physics Department Laboratory, FMIPA-UNJ. The research carried out is research and development. This machine (the media) can show electric charge jumps directly from the friction between aluminum foil (sector) and brass as a rake. The results of the Wimhurst machine are learning media in the form of teaching aids that can help teachers in conveying material and can develop science process skills. The results of testing the Wimhurst machine teaching aids can attract students' interest in studying static electricity, so that students can easily understand the concept of static electricity.


INTRODUCTION
In the physics learning process, the use of learning media has become important, this is because physics is a subject that has quite complicated, abstract and imaginative discussions so students have to exhaust their minds to be able to understand a concept.At a time when technological advances are currently developing, the visualization of the existence of applications of physics tools can be optimized to help students understand physics concepts at school.The use and development of learning media can arouse students' interest in being directly involved and can stimulate students to be active in the learning activities, and learning media, students can experience directly the new knowledge conveyed by the teacher.
One of the materials in physics lessons that is quite complicated and abstract is static electricity.This is due to the lack of appropriate learning media for explaining static electricity material.The learning CSER media in this case are the teaching aids, which are often displayed in textbooks, usually plastic combs with wool cloth and glass with silk cloth (Kanginan, 2011).Apart from that, the methods used by teachers at school still use conventional methods; as a result, students can only listen and see the teacher's explanations.This does not help students in describing the process of static electricity phenomena.The lack of learning media also affects students ability to describe basic concepts in static electricity.In the learning process, teachers usually talk about electrical events in everyday life, even though these events can be created by the teacher and involve students directly.Apart from increasing students' interest in the learning process, another reason this research was conducted was for future educational trends.According to Miarso (1990) (in the book Sowing the Seeds of Educational Technology, Miarso (2009:267)): (1) learning to investigate or learning to discover (discovery learning) (2) independent learning (3) Diversity of sources (4) differentiation of roles and ( 5) scientific approach.A teacher must assist an educational institution in developing learning resources.According to Yusuf Hadi Miarso (2009:296) a transformative institution will be able to develop and manage learning programs based on various sources.These various sources are anything that has been deliberately developed or is already available and contains the potential for use in learning organizations.
According to Bringgs (1970) (in M. Rohman, Learning Media, 2013: 156), learning media are all physical tools that can produce messages and stimulate students to learn.According to Rohman (2013: 156), the learning media used in schools have the following objectives: (1) to make it easier for them to better understand certain concepts, principles, and skills; (2) to provide different and varied learning experiences so as to further stimulate their interest and motivation to learn; (3) to foster certain attitudes and skills in technology because they are interested in operating certain learning media; (4) to create a learning situation that students cannot overcome; (5) to clarify information or learning messages; (6) to improve the quality of teaching and learning.There are several types of learning media, one of which is a teaching aid.
According to Sudjana (2000:110) teaching aids are tools used by teachers in the teaching process so that the student learning process is more effective and efficient.According to Ratmawijaya (1979:28) teaching aids are auxiliary or complementary tools used by teachers in communicating with students.According to Hamzah (1981) (in Sudjana Metode Statistika.2000: 110), educational teaching aids are tools that can be seen and heard to make communication effective."Accordingto Nasution (1985:95) teaching aids in Gino (1998:51) are "tools to help teach more effectively."According to Rohani (1995:24) props are divided into two types, namely: (1) direct props, and (2) indirect props.
The Wimhurst machine was made by James Wimhurst in 1883.The Wimhurst machine can produce electrical jumps based on the number of disks used along with the diameter used, as well as the distance between the disks.Small pieces of aluminum called "sectors" attached to the outer surface of the disk will help to drain excess electrical charge from the disk.

FIGURE 1. WIMHURST MACHINE
Using the right learning model can also increase the efficiency of the learning process.The hands-on activity learning model is one of the appropriate learning models in solving problems of difficulty CSER understanding basic concepts, because the hands-on activity learning model requires all students to use several learning media (props) and conclude a phenomenon that occurs when using them.the learning media.Developing a static electricity learning media in the form of a Wimhurst machine to explain the process of lightning, and a hands-on activity learning model will be carried out in testing the Wimhurst machine learning media so that students can understand the basic concepts of static electricity phenomena in everyday life.

METHOD
This research method is a development model (Research and Development).The subjects of this research were eighth-grade junior high school students.This research was conducted at the Physics Mechanics Laboratory, Physics Department, FMIPA, Jakarta State University.This research is focused on developing learning media in the form of teaching aids.
Development research is carried out through the stages of preliminary study, initial media design, media creation, media testing, media validation, media testing on teachers and students, and making reports.In the media validation process, if the media is not suitable, it will be reviewed from a manufacturing perspective and correct any deficiencies in the media.

Requirements Analysis Stage
The initial needs analysis stage was carried out with the aim of finding out the needs and constraints of teachers and students in learning physics regarding static electricity.Identifying their needs regarding the creation of learning support media in the form of Wimhurst machines in junior high schools.
Based on the results of the needs analysis questionnaire, it can be concluded that the majority of students like physics practicum, which can be seen from the results of the needs analysis questionnaire with a percentage of 88.52%.In practice, teachers very rarely conduct experiments, around 1-2 practicums in one semester.Then, based on the questionnaire, data was obtained that 100% did not know and use the Wimhurst machine, and 91.80% of respondents supported and were interested in the development of supporting physics learning in the form of teaching aids in the form of the Wimhusrt machine.
Based on this data, it is necessary to have teaching media supporting physics teaching aids as an alternative learning media in junior high schools to support learning.With the production of the automatic Wimhurst machine, it is hoped that it will become a medium that supports students in learning junior high school physics.

Learning Media Design
The manufacturing stage begins with determining the initial design of the static electricity learning media (Wimhurst machine).The initial design was based on developments in the Wimhurst engine.With the following media design: The induction source is made of circular acrylic material with a diameter of 23.6 cm, totaling 2, surrounded by aluminum foil, totaling around 20.The two acrylics are connected to a pulley with a silk belt, one of the belts is installed upside down so that it can rotate in the opposite direction.In this induction source there are also 2 pairs of rakes made of stainless steel and brass fibers as aluminum foil rakes.The total height of the induction source section is 30.5 cm.

FIGURE 3. INDUCTION SOURCE
In the electric charge storage and release section there are several parts, including the Leiden Jar, charge neutralizer (collector) and electric charge release rod.The Leiden Jar is made from plastic in the shape of a bottle with a diameter of 4.93 cm and a height of 19.8 cm.Some of the inner and outer covers of the bottle are covered with aluminum so that it can store the charge from the induction source.
The neutralizer (collector) and release of the electric charge are made of stainless steel, in the neutralizer (collector) of the charge there is a pointed part which aims to attract the electric charge from the friction of the aluminum foil with brass at the induction source.In the electric charge release section there are two large balls and two small balls made of stainless steel, for the large size it has a diameter of 18.80 mm and for the small size it has a diameter of 8.84 mm, at the end of the charge release it is provided with plastic material so that when it is used students/tool users are not struck by electricity as a result of induction.

CSER FIGURE 4. LAIDEN JAR AND DISCHARGER ELECTRIC CHARGE
The controller section consists of a dynamo with a delta box type (full gear set) with an input voltage of 24 volts which is directly connected to the induction source with a silk belt.There is also an electrical circuit that provides a timer so that the turning machine can turn off automatically.On the controller button there is an on button and a potentiometer which is useful for adjusting the speed given to the induction source.With A speed of 17 rpm, B speed of 50 rpm and C speed of 70 rpm.The part where the electrical circuit and motor are located is provided with a hinge so that it can lock the box, which aims to provide security for the user.

Media Testing
This prop has 20 pieces of aluminum foil on each 2 acrylic circles, with 2 scratching sticks made of brass.The way this tool works is that the acrylic disk rotates with the help of a dynamo and controller which have different speeds, so that the sector (aluminum foil) rubs against the brass rake.As a result of this friction, there is a change in charge in the sector.The excess electric charge in the sector is then channeled to the charge collecting electrode (Leiden jar) as a capacitor.
If the charge in the Leiden jar is full, the charges are directly channeled to the electrode release which is made of spherical stainless steel.The electric charges that have accumulated at the end of the ball create a very strong electric field that is able to polarize the surrounding air, so that it can attract electric charges from the end of the electrode ball to the other electrode ball.

CSER FIGURE 6. WIMHURST MACHINE
This media has three (3) different speed variations, namely (1) speed A with a rotational speed of 18 rpm; (2) speed B with a rotational speed of 50 rpm; and (3) speed C with a rotational speed of 70 rpm.These three rotational speeds result in different jumps in the resulting electric charge.The following are the results of the experiments that have been carried out: This is because, the faster the circle rotates, the friction that occurs between the aluminum foil and brass will occur more frequently compared to at a low speed, as a result the charge changes on the aluminum foil will be greater and the electric charge will jump more.

FIGURE 7. ELECTRIC CHARGE JUMPS IN BRIGHT CONDITIONS FIGURE 8. ELECTRIC CHARGE JUMPS IN DARK CONDITIONS
The distance between the discharge electrodes can also affect the number of electric charge jumps.On the discharge electrode the two distances can be adjusted.The teaching aids were tested at certain distances, namely 0.5 cm, 1 cm and 2 cm.The results of the props experiment are as follows:  The different total jumps are because the electric field produced will be smaller at greater distances, so that the electric charge cannot move as easily as when the distance between the electrodes is close to one another.
All the experiments that have been carried out are also greatly influenced by the condition of the sector (aluminum foil) used, with very frequent use it can result in the sector being eroded, so that changes in the type of electrical charge in the sector are not as good as in the initial state which had not yet been eroded by the brass.

Media Validation
Media validation is carried out by media experts and material experts.Media expert validation was carried out at Taman Mini Indonesia Indah (TMII) and material validation was carried out at Jakarta State University (UNJ).The following are the results of media expert validation: Based on the above aspects, the three assessment aspects, including suitability of content, suitability of concepts and exploration of science process skills, obtained a very good assessment level, namely in the score interpretation range of 80-100% (very good).
The following are the results of the validation from the material expert team:

CSER FIGURE 10. MEDIA EXPERT TEAM VALIDATION RESULTS
Based on the above aspects, the two aspects of assessment, namely media content (content) and design, obtained a very good level of assessment on media content (content), namely in the score interpretation range of 80-100% (very good) and obtained a good level of assessment on product design with a range of 60-79.99%(good).
Validation of teaching aids is related to the suitability of core competencies in the 2013 curriculum and the use of teaching aids as learning aids in schools to help students achieve the core competencies that must be achieved.
The teaching aids that have been produced must be in accordance with the concept of static electricity and not give rise to misconceptions.Also, the props must be attractive, practical and easy to use so that they can attract students' attention when used in the learning process.The Wimhurst machine is expected to provide students with a more direct and concrete learning experience.
After validation tests were carried out by experts, comments and suggestions were obtained which would later be used by researchers to improve and add value to the Wimhurst machine trainer.Based on the material expert team, the suggestions given by the material expert team include: 1. Determine where the electrons that jump or splash between the two electrode balls come from 2. Develop an instrument to measure student competency in static electricity material in the form of a performance test 3. Equip the visual aids with a rotational speed measuring instrument so that you can see the relationship between rotational speed and load jump 4. Increase the rotational speed of the induction source 5. Provides more speed variations 6. Adding packaging (storage box) And based on the media expert team, the suggestions given by the media expert team include: 1.The safety aspect of the teaching aids is still not good 2. The durability of the tool is still not good 3.It should be demonstrated and equipped with other supporting scientific information 4. The production of props was developed by making them in larger sizes 5. Props are added with additional components that are even more interactive 6. Need to add an operation manual