By projected aids we mean those aids where a bright light is passed through a transparentPicture and by means of a lens, an enlarged picture is thrown or projected on the screen.DIFFERENT TYPES OF PROJECTED AIDS ARE; OPAQUE PROJECTIONS TRANSPARENT STILL PROJECTIONS CINE PROJECTIONS
The projection of real magnified images on a screen directly from pictures and drawings on papers is called opaque projections. Opaque projection requires a fully darkened room in order to show details and colouring satisfactorily
PRINCIPLE;;THE LIGHT REFLECTED FROMTHE STRONGLY ILLUMINATEDPICTURE IS REVERSED BYMEANS OF A MIRROR AT45DEGREE AND THEN IT ISPROJECTED ON A SCREENUSING A CONVEX LENS,THEILLUMINATED PICTURE LIESBETEWEEN THE FOCUS ANDTWICE THE FOCUS OF THECONVEX LENS TO PRODUCEREAL MAGNIFIED IMAGES
Opaque projection is done by an optical instrument called epidiascopeDifferent models
ADVANTAGES Stimulates attention Arouse interest Provide information Help students to retain knowledge for a longer period of time To introduce a specific topic there is no need of tearing it off from book
It needs a dark room for projectionAs it is large in size, it is immovable
A slide is a of70mm,35mm,or6mm size whichis opticallyenlarged andprojected as areal image
It is used for projectingpictures from atransparent slide on awall or screen. As it isused to project slides, itis called a slideprojector. It helps inshowing the magnifiedimage of the Slides.Also It can be operatedand focused by remotecontrol.
It is light and easy to transport It arouses attention and interest Slide projector is not costly. It is very easy to use. The picture on the screen can be allowed to remain there as long as the students wish
Time consuming program Needed a dark surrounding
An optical instrument with two eyepiecesused to impart a three-dimensional effect totwo photographs of the same scene taken atslightly different angles.
It present a realistic view,which stimulates interestof student
The name ‘Overhead projector’ comes from the fact that the projected image is behind and over the head of the speaker/teacher. In overhead projection, a transparent visual is placed on a horizontal stage on top of light source. The light passes through this transparency and then is reflected at 90° angle on the screen at the back of the speaker.
OVER HEAD PROJECTER DEMONSTRATION IN A CLASS ROOM
It is simple, easy and convenient to operate the overhead projector Effective visuals can be made in a minimum of time and at low cost Easier to write on horizontal surface of transparencies O.H.P. can operate in an illuminated room. There is no need of darkening the room
1. Cannot be used for long time.2. Writing by some types of writing pens get blotted out on plastic.3.Transparencies create a storage problem
It is an improvement upon slide projector.Instead of using different slide for differenttopics or more slides for one topic, one stripor piece of still film is prepared. Slidesproduced on films are called film strips.
It is easy to operate Strips of educative value are available according to special needs It draws the attention of the students Varieties of information may be given. Film strips are light weight and easy to carry.