Power Of Lens
Power of a lens is the measure of how strongly it converges or diverges light.
Practice This ConceptMain explanation
Teacher explanation
Power is the reciprocal of focal length in metres: P = 1/f. A convex lens has positive power because it converges light, while a concave lens has negative power because it diverges light. The unit is dioptre.
Example
A lens with focal length 0.5 m has power +2 D.
Simple analogy
Shorter focal length means stronger power.
Common confusion
Students forget to convert centimetres into metres before finding power.
Exam tip
Always write the sign of power with the lens type: convex positive, concave negative.
Answer writing and exam use
1-mark use
Write the exact meaning of power of lens in one clean line.
2-mark use
Define power of lens and add one example or condition.
3-mark use
Explain power of lens, show the method or example, and mention the common mistake.
Practice this concept with focused MCQs
Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.
Help improve this page
Found something confusing, incorrect, or missing?