Which one of the following statements is not correct?
The radius of curvature of a concave mirror is twice its focal length
Power of a convex lens is negative and that of a concave lens is positive
The radius of curvature of a plane mirror is infinity
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
Answer is Right!
Answer is Wrong!
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.