The power of a concave lens is_______________?
Correct answer: D. negative
- A. real
- B. virtual
- C. positive
- D. negative
Explanation
A concave lens causes parallel rays to diverge, so its focal point is virtual and its focal length is negative. Since lens power P = 1/f when f is measured in metres, its power is negative and measured in dioptres. Students may choose positive by remembering only that power describes lens strength, not its converging or diverging nature.
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About Optics
Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
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