Q1
A magnifying glass uses a:
Aconvex lens
Bconcave lens
Cplane mirror
Dconcave mirror
CBSEClass 8 (CBSE)ScienceCh 10 · Topic 2
Refraction by Lenses
Learning how convex and concave lenses bend light to form images.
Core concept
Convex lenses are used in magnifying glasses (to enlarge close objects), cameras, and to correct long-sightedness (hypermetropia), while concave lenses are used to correct short-sightedness (myopia) by diverging light before it enters the eye. The power of a lens, measured in dioptres (D), indicates how strongly it converges or diverges light — calculated as the reciprocal of its focal length in metres (Power = 1/focal length), with convex lenses having positive power and concave lenses having negative power.
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• Convex lens: thicker in the middle, converges light; can form real or virtual images.
• Concave lens: thinner in the middle, diverges light; always forms a virtual, diminished image.
• Convex lenses used in magnifying glasses, cameras; correct long-sightedness.
• Lens power (in dioptres) = 1/focal length (metres); convex is positive, concave is negative.