Light – Reflection and Refraction | Class 10 Science Notes

9.3.4 Image Formation by Lenses

Lenses form images by refracting light rays. For a convex lens, the nature, position, and size of the image depend on the object's position relative to the focal points (F1, F2) and twice the focal length (2F1, 2F2). When the object is at infinity, the image forms at the focus, highly diminished and real. Beyond 2F1, the image forms between F2 and 2F2, diminished and real. At 2F1, the image forms at 2F2, same size and real. Between F1 and 2F1, the image forms beyond 2F2, enlarged and real. At F1, the image forms at infinity. Between F1 and optical center O, the image forms on the same side as the object, enlarged, virtual, and erect. For concave lenses, images are always virtual, erect, and diminished regardless of object position. Activities with candles and lenses help observe these image characteristics. Tables 9.4 and 9.5 summarize these observations.

📊 Diagram: Table on page 19 summarizing image formation by convex lens; Table on page 20 summarizing image formation by concave lens.

🧪 Activity: Activity 9.12: Observing image formation by convex lens for various object positions; Activity 9.13: Observing image formation by concave lens.

🔗 Connection: Leads to ray diagrams for lenses and sign conventions.

Table on page 19 (7×4)

Table on page 20 (3×4)