Which one of the following statements is not correct?
[amp_mcq option1=”The radius of curvature of a concave mirror is twice its focal length” option2=”Power of a convex lens is negative and that of a concave lens is positive” option3=”The radius of curvature of a plane mirror is infinity” option4=”When a ray of light passes from an optically denser medium to an optically rarer medium, the angle of refraction is greater than the corresponding angle of incidence” correct=”option2″]
This question was previously asked in
UPSC NDA-2 – 2015
– Statement B is incorrect. The power of a lens (P = 1/f) is positive for a converging lens (convex lens) because its focal length (f) is positive. The power of a diverging lens (concave lens) is negative because its focal length (f) is negative.
– Statement C is correct. A plane mirror can be considered as a part of a spherical mirror with an infinite radius of curvature. Consequently, its focal length (f = R/2) is also infinite.
– Statement D is correct. According to Snell’s Law, when light travels from a denser medium (higher refractive index n₁) to a rarer medium (lower refractive index n₂), it bends away from the normal. This means the angle of refraction (θ₂) is greater than the angle of incidence (θ₁), as n₁ sin θ₁ = n₂ sin θ₂ and n₁ > n₂, implies sin θ₂ > sin θ₁, leading to θ₂ > θ₁.