Quick Answer: The Convex Lens is a double convex spherical lens of +20D power and 50 mm focal length, used to demonstrate converging rays, focal length and real image formation in ray optics practicals.
Last updated: October 2026
Key Features
Double convex spherical lens
Power +20D with 50 mm focal length
38 mm diameter
Optically worked faces with ground edges
Refractive index approximately 1.52
Technical Specifications
Specification
Value
Lens type
Double convex spherical lens
Power
+20D
Focal length
50 mm
Diameter
38 mm
Refractive index
1.52 approx.
Finish
Optically worked faces with ground edges
About This Product
In a lens holder or on an optical bench, the lens is aligned with a ray source, light box or object, and students watch parallel rays converge after passing through it. Moving a screen until the image or focal point is sharp, then measuring the lens-to-focus distance, gives the focal length for comparison with a standard ray diagram. It suits lessons on lens power, magnification and ray tracing.
Frequently Asked Questions
Q1. How do the power and focal length of this lens relate? Power in dioptres is the reciprocal of focal length in metres, so the +20D power corresponds to the 50 mm focal length.
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