Practical-1.pptx uses and principles of overhead projector in extension education

this is to teach undergraduate students on communication technique as OHP.

1. Title: Use and Principles of Overhead Projector Dr. Sudarshan Prasad Regmi Objectives: To know different parts and uses of Overhead Projector To Understand the Principles of operation of OHP. To be able to operate and demonstrate presentation by OHP

2. Overhead Projector (OHP) Overhead projector projects any transparent instructional item such as charts, graphs, drawings, pictures etc., on to the screen. The overhead projector (OHP) is a device commonly used in classrooms and presentations to display images or text onto a screen or wall. It works on the principle of using light to project an image onto a transparent sheet placed on the projector's stage. Overhead projectors are commonly used in educational and business settings, where they are used to give presentations, lectures, or training sessions. They can also be used in artistic and creative contexts, such as in the creation of murals or other large-scale artworks. While overhead projectors have been largely replaced by digital projectors and other newer technologies, they remain a simple and effective tool for visual communication and are still used in some settings . Principle Overhead projectors function under the principle of indirect projection. Here are the key principles of an overhead projector : 1. Light source 2. Transparency : 3. Optics : 4. Stage : 5. Projection : 6. Controls :

3. Light Source : The OHP uses a bright light source, typically a halogen lamp, to illuminate the transparent sheet. The light passes through the sheet and projects the image onto a screen or wall. Transparency : The image or text to be projected is printed or written on a transparent sheet, also known as an overhead transparency. The transparency allows light to pass through it, making the image visible when projected. Optics : The OHP has a set of lenses and mirrors that focus and direct the light from the lamp onto the transparency. The lenses ensure that the image is properly focused and enlarged for clear projection. Stage : The stage of the OHP is a flat surface where the transparency is placed. It is usually made of glass or plastic and has a mechanism to hold the transparency in place. The stage is adjustable to position the transparency correctly for projection. Projection : When the light passes through the transparency, it is projected onto a screen or wall. The projected image appears larger and clearer, making it visible to a larger audience. Controls : The OHP typically has controls to adjust the brightness of the lamp, focus the image, and control the position of the transparency on the stage. These controls allow the presenter to optimize the projection for better visibility.

4. Working Principal Rays of light come from a projection lamp, enter one element of the condenser lens unit and are reflected by a plane mirror placed at an angle of 45 degree with either of the axis of the condenser unit. The reflected rays enter the other element of the condenser unit, pass through the slide or transparencies, enter the objective lens and are again reflected by another plane mirror placed at an angle of 45 degree with the axis of the objective lens to form an enlarged image of the material on the screen. The loss of light is more when compared to direct projection . Overhead Projector Projector Screen

5. Different Parts of OHP

6. PROCEDURE Planning Decide on the theme on which the slides have to be prepared. Make a written program of writing Subject matter or presentation. Preparation Making of transparency Use a transparent sheet or film, known as a transparency . Arrange in an order for sequential presentation Projection of written content The transparency is placed on a glass plate, known as the stage. Size of projection stage 250 x 250 mm. Switch on the overhead projector Equipped with 24V 250 watts, halogen lamp Arrangement of Projector Screen or wall Presentation Introduce the topic and explain briefly about the major points. Announce about the projection of different topics Project the transparency one by one and explain them to the audience.

7. ADV ANTAGES OF USING OHP Lecture can use it in same way as a chalk board or marker board . Lecture  can always face  the class. Lecture  can maintain  eye contact with the student. Lecture  can use it again  and again . OHP serves both as an outward non- verbal  communication  channel for  the teacher and as a means of obtaining feed back form the class on how a session is going . OHP can be used to show pre –prepared material.  The  material projected can be changed easily and quickly, shapes can be presented and compared, colors may be included and exposure can be controlled. OHP  does not need room to blackout.  ie . It can be used in  welllighted room. Users  friendly and does  notrequire  any technical skills or knowledge.

8. DISADVANTAGES OF USING OHP It requires power supply. It need a suitable flat surface on which to project its image. Unless the surface is  inclined forward  at the correct angle, the  image will probably suffering from key stoning. It requires certain amount of routine maintenance. Liable to break down occasionally if handled improperly. Its is always advisable to have spare bulb Some lectures find glare from OHP .    It is advised not to move  OHP immediately  as soon as the lamp  is switched off . Apart from these possible hardware difficulties, other problems are: Writing OHP sheet too small. Untidy written OHP sheets will makes the students difficult to read.

9. Practical Exercise Prepare Transparencies on and Demonstrate about following Issues on OHP: Artificial Insemination for (RN. 1-2); / ( RN. 16-17) Cattle Breeds of Nepal for (RN. 3-4); / ( RN. 18-19) FMD disease in Nepal for (RN. 5-6); / ( RN. 20-21) Pig breeds of Nepal for (RN. 7-8); /( RN. 22-23) Major Fodder trees of Nepal for (RN. 9-10 ); / (RN. 24-25) Milk production in Nepal ( RN. 11-12 );/ ( RN. 26-27) Vaccination in Poultry (RN. 13-15 );/ ( RN. 28-29) Note: RN. = Roll Numbers; A1= from RN. 1-15; A2= 16-29.