What is an Overhead Projector?

An Overhead Projector (OHP) is a teaching device used to display text, diagrams, charts, and images from a transparent plastic sheet (transparency) onto a screen or wall. It allows the teacher to present information to a large group of students while facing the class.

Main Parts of an Overhead Projector

  1. Lamp (Light Source): Produces bright light.
  2. Glass Stage: Holds the transparency sheet.
  3. Mirror: Reflects the light upward.
  4. Projection Lens: Focuses and enlarges the image.
  5. Projection Head/Arm: Directs the image to the screen.
  6. Cooling Fan: Prevents the lamp from overheating.

 

Working of an Overhead Projector

  1. Place the transparency sheet on the glass stage.
  2. Switch on the projector.
  3. The lamp shines light through the transparency.
  4. The mirror and lens enlarge and project the image onto the screen.
  5. Adjust the focus until the image becomes clear.

 

Advantages of an Overhead Projector

  • Easy to operate and maintain.
  • Displays information to a large audience.
  • Teacher can face students while teaching.
  • Transparencies can be reused many times.

 

Disadvantages of an Overhead Projector

  • Requires electricity to operate.
  • Bulb may become hot or burn out.
  • Limited to transparent sheets only.

 

Handling of Overhead Projectors

Before Using the OHP

  • Place the projector on a stable and flat table.
  • Ensure the power cord is connected safely.
  • Clean the glass stage and projection lens.
  • Keep the screen clean and properly positioned.
  • Use clean, wrinkle-free transparency sheets.

During Use

  • Switch on the projector only when needed.
  • Place the transparency correctly on the glass stage.
  • Adjust the focus for a sharp image.
  • Do not block the ventilation openings.
  • Avoid touching the hot lamp or lens.
  • Keep food and liquids away from the projector.

After Use

  • Switch off the projector.
  • Allow it to cool before moving or storing it.
  • Remove the transparency sheet.
  • Clean the glass stage with a soft cloth.
  • Cover the projector to protect it from dust.
  • Store it in a dry and safe place.

 

 

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