Ray Diagrams for Lenses

Convex Lens

• Focal Length: 10 cm
• Object Position: 30 cm
• Key Points:
  • Focus: 10 cm from optic center
  • 2F (Twice the Focal Length): 20 cm from optic center
  • Object at 30 cm is beyond 2F

Ray Diagram Construction

1. Draw the Lenses: Mark focal points and 2F.
2. Draw Rays:
   • Ray 1: From the top, parallel to the principal axis, refracts through the principal focus.
   • Ray 2: Through the optic center, goes undeviated.
   • Ray 3 (Optional): Through principal focus, refracts parallel to the principal axis.

Image Characteristics

• Position: Between F and 2F (10 cm and 20 cm)
• Nature: Inverted (Real Image)
• Size: Diminished

Additional Cases

• Object at 2F:
  • Image at 2F, same size, real and inverted.
• Object between F and 2F:
  • Image beyond 2F, magnified, real and inverted.
• Object at F:
  • Rays are parallel, no image formed.
• Object between F and O:
  • Rays diverge, virtual, erect, enlarged image.

Concave Lens

• Ray Diagram Construction:
  • Parallel Ray: Diverges, appears to come from focus.
  • Ray through Optic Center: Goes undeviated.

Image Characteristics

• Nature: Virtual, erect.
• Size: Always diminished.
• Position: Between F and O, regardless of object location.

Summary

• Convex vs. Concave:
  • Convex lenses can produce real or virtual images based on object position.
  • Concave lenses always produce a virtual image.
• Method: Drawing two rays helps determine image properties (size, position, nature) for any lens scenario.