CBSE Class 12 Physics 2025: question 30

Q30 · 4 marks · Case-basedCompetency-basedRay Optics and Optical Instruments

1. (i)

   A small bulb is placed at the bottom of a tank containing a transparent liquid (refractive index n) to a depth H. The radius of the circular area of the surface of liquid, through which light from the bulb can emerge out, is R. Then $\left(\frac{R}{H}\right)$ is :

   1. (A)$\frac{1}{\sqrt{n^2-1}}$
   2. (B)$\sqrt{n^2-1}$
   3. (C)$\frac{1}{\sqrt{n^2+1}}$
   4. (D)$\sqrt{n^2+1}$

   1 mark
2. (ii)(a)

   A parallel beam of light is incident on a face of a prism with refracting angle $60^{\circ }$. The angle of minimum deviation is found to be $30^{\circ }$. The refractive index of the material of the prism is close to :

   1. (A)1·3
   2. (B)1·4
   3. (C)1·5
   4. (D)1·6

   1 mark

3. OR

   (ii)(b)

   The angle of minimum deviation for a ray of light incident on a thin prism, made of crown glass (n = 1·52) is $D_m$. If the prism was made of dense flint glass (n = 1·62) instead of crown glass, the angle of minimum deviation will :

   1. (A)decrease by 4%
   2. (B)increase by 4%
   3. (C)decrease by 19%
   4. (D)increase by 19%

   1 mark
4. (iii)

   An object is placed in front of a convex spherical glass surface (n = 1·5 and radius of curvature R) at a distance of 4R from it. As the object is moved slowly close to the surface, the image formed is :

   1. (A)always real
   2. (B)always virtual
   3. (C)first real and then virtual
   4. (D)first virtual and then real

   1 mark
5. (iv)

   A double-convex lens, made of glass of refractive index 1·5, has focal length 10 cm. The radius of curvature of its each face, is :

   1. (A)10 cm
   2. (B)15 cm
   3. (C)20 cm
   4. (D)40 cm

   1 mark