Home › UP Board Class 10 › physics › c10lensformula › Per NCERT, if a lens has POWER = −2.5 D, what is…
Per NCERT, if a lens has POWER = −2.5 D, what is its FOCAL LENGTH — and is it convex or concave?
Af = +0.40 m; concave
Bf = −10 m; convex
Cf = −0.40 m (= 1/(−2.5)); negative power and negative f indicate it is a CONCAVE lens
Df = −2.5 m; convex
Answer & Solution
Correct answer: C. f = −0.40 m (= 1/(−2.5)); negative power and negative f indicate it is a CONCAVE lens
Per NCERT §9.3.8, f = 1/(−2.5) = −0.40 m. Negative → concave.
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