Every Book Back multiple-choice question from Ray Optics (12th Standard Physics, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
The speed of light in an isotropic medium depends on,
- A. its intensity
- B. its wavelengthCorrect
- C. the nature of propagation
- D. the motion of the source w.r.t medium
Explanation. In a medium, the refractive index varies with wavelength according to Cauchy's relation, causing the speed of light to depend on its color.
Q2
A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is, (AIPMT Main 2012)
- A. 2.5 cm
- B. 5 cmCorrect
- C. 10 cm
- D. 15 cm
Explanation. The positions of the rod's ends are found using the mirror formula. The difference between these two image distances determines the rod's total image length.
Q3
An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified. (JEE Main 2009)
- A. 2f and c
- B. c and \(\infty\)
- C. f and O
- D. None of theseCorrect
Explanation. Convex mirrors always produce virtual, upright, and diminished images for real objects, so forming a real magnified image is physically impossible.
Q4
For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is,
- A. \(30^\circ\)Correct
- B. \(45^\circ\)
- C. \(60^\circ\)
- D. \(90^\circ\)
Explanation. The maximum angle of refraction occurs when light is incident grazing the surface at ninety degrees, which is solved using Snell's law.
Q5
If the velocity and wavelength of light in air is \(V_a\) and \(\lambda_a\) and that in water is \(V_w\) and \(\lambda_w\), then the refractive index of water is,
- A. \(V_w/V_a\)
- B. \(V_a/V_w\)Correct
- C. \(\lambda_w/\lambda_a\)
- D. \((V_a \lambda_a)/(V_w \lambda_w)\)
Explanation. Refractive index is defined as the ratio of the speed of light in air or vacuum to its speed in the specific medium.
Q6
Stars twinkle due to,
- A. reflection
- B. total internal reflection
- C. refractionCorrect
- D. polarisation
Explanation. Twinkling occurs because star light undergoes continuous refraction while passing through different layers of the Earth's atmosphere with varying refractive indices.
Q7
When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index,
- A. less than one
- B. less than that of glass
- C. greater than that of glass
- D. equal to that of glassCorrect
Explanation. According to the lens maker's formula, the focal length becomes infinite when the refractive indices of the lens and surrounding medium are equal.
Q8
The radius of curvature of curved surface at a thin planoconvex lens is 10 cm and the refractive index is 1.5. If the plane surface is silvered, then the focal length will be,
- A. 5 cm
- B. 10 cmCorrect
- C. 15 cm
- D. 20 cm
Explanation. The effective focal length is calculated by combining the powers of the refracting surfaces and the reflecting silvered surface as light passes through.
Q9
An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is,
- A. 8 cm
- B. 10 cm
- C. 12 cmCorrect
- D. 16 cm
Explanation. The actual depth from each surface is found by multiplying apparent depth by refractive index, then adding them to find the slab's thickness.
Q10
A ray of light travelling in a transparent medium of refractive index n falls, on a surface separating the medium from air at an angle of incidence of \(45^\circ\). The ray can undergo total internal reflection for the following n,
- A. n = 1.25
- B. n = 1.33
- C. n = 1.4
- D. n = 1.5Correct
Explanation. For total internal reflection, the refractive index must be greater than the reciprocal of the sine of the angle of incidence.
About these Ray Optics questions
These are the Book Back multiple-choice questions for Ray Optics from the Tamil Nadu State Board (Samacheer Kalvi) 12th Standard Physics syllabus. Each question shows the correct option and an original, step-by-step explanation so you understand the method, not just the answer. Use the answer key above to jump to any question, then take the practice test to check yourself under exam-like conditions.
Frequently asked questions
How many MCQs are there in Ray Optics?
This chapter has 10 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Physics MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Ray Optics book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
