Lecture on Drawing Ray Diagrams for Lenses

Overview

• Focus on drawing ray diagrams for convex (converging) and concave (diverging) lenses.
• Applications include understanding how light behaves when passing through lenses.

Concave Lenses (Diverging)

• Symbol: Outwards pointing v-shapes at either end, showing lens widening towards ends.
• Axis: Horizontal line through the middle of the lens.
• Focal Points:
  • One on each side of the lens, also called the principal focus.
  • Points labeled as "F".
  • Additional points labeled "2F", twice the distance from the lens as "F".

Ray Diagram Steps for Concave Lenses

1. Object Placement: Example given with a chicken as the object.
2. Incident Rays:
   • Draw a ray parallel to the axis.
   • Draw another ray towards the lens center.
3. Ray Behavior:
   • Ray through center: continues straight, un-refracted.
   • Parallel ray: refracted following a virtual ray towards the focal point (drawn as dashed line).
4. Image Formation:
   • Locate where rays cross to find image position.
   • Image properties: virtual (due to virtual ray), upright, smaller than the object.

Convex Lenses (Converging)

• Symbol: V-shapes pointing inwards, showing lens narrowing towards ends.

Ray Diagram Steps for Convex Lenses

1. Setup: Similar to concave, with axis, focal points, and object.
2. Incident Rays:
   • Draw a ray parallel to the axis; passes through the focal point after refraction.
   • Draw another ray through the lens center; continues straight.
3. Image Formation:
   • Locate where rays cross to determine image location.
   • Image properties: real (with real rays), inverted (upside down), smaller.

Special Cases for Convex Lenses

• Object at 2F: Image is real, inverted, same size as object.
• Object between F and 2F: Image is real, inverted, larger.
• Object between F and Lens:
  • Refracted rays do not meet, use virtual rays for tracing.
  • Image properties: virtual, upright, larger.

Exam Tips

• Typically, simple objects like arrows are used instead of complex shapes.
• Always draw rays from the top of the object to ensure accuracy.

Conclusion

• Summarized how to draw and analyze ray diagrams for concave and convex lenses.
• Importance of understanding image properties such as size, orientation, and type (real or virtual).