This will help you to learn things

1. Lenses
Class 10 Science – Light: Reflection
and Refraction

2. Introduction to Lenses
• Lenses are transparent optical devices that
converge or diverge light rays.
• Two Types:
• • Convex Lens (Converging)
• • Concave Lens (Diverging)

3. Types of Lenses
Lens Type Shape Nature Effect on Light
Convex Thick at center Converging Brings rays together
Concave Thin at center Diverging Spreads rays apart

4. Key Terms
• • Optical Centre (O): Midpoint of lens
• • Principal Axis: Line through center
• • Focus (F): Point where rays meet/diverge
• • Focal Length (f): Distance between O and F

5. Ray Diagrams – Convex Lens
• Draw diagrams for object positions:
• • At Infinity
• • Beyond 2F
• • At 2F
• • Between F and 2F
• • At F
• • Between F and O

6. Ray Diagrams – Concave Lens
• Draw for object placed anywhere.
• Image is always virtual, erect, and diminished.
• Use two rays:
• • Parallel to axis
• • Through optical center

7. Image Characteristics Summary
Lens Type Object Position Image Nature Image Position
Convex Beyond 2F Real, Inverted Between F & 2F
Convex At 2F Real, Inverted At 2F
Convex Between F & 2F Real, Inverted Beyond 2F
Convex At F No image --
Convex Between F & O Virtual, Erect Same side
Concave Anywhere Virtual, Erect Same side

8. Lens Formula
• Lens formula:
• 1/f = 1/v - 1/u
• • f = focal length
• • v = image distance
• • u = object distance
• Sign convention: All distances measured from
optical center

9. Power of a Lens
• P = 100 / f (in cm)
• Unit: Diopter (D)
• • Convex: Positive
• • Concave: Negative

10. Uses of Lenses
• Convex:
• • Magnifying glass
• • Camera lenses
• • Human eye
• Concave:
• • Spectacles for myopia
• • Peepholes in doors

11. Recap
• • Types of lenses and properties
• • Image formation and ray diagrams
• • Lens formula and power
• • Real-life uses

12. Thank You
• Any Questions? 😊