(a) (i) An object is placed $30\text{ cm}$ from a thin convex lens of focal length $10\text{ cm}$. The lens forms a sharp image on a screen. If a thin concave lens is placed in contact with the convex lens, the sharp image on the screen is formed when the screen is moved by $45\text{ cm}$ from its initial position. Calculate the focal length of the concave lens. (ii) Calculate the angle of minimum deviation of an equilateral prism. The refractive index of the prism is $\sqrt{3}$. Calculate the angle of incidence for this case of minimum deviation also. OR

Year	Paper Code	Set	Position
CBSE 2025	Series 55-4	Set 1	Question 33
CBSE 2025	Series 55-4	Set 2	Question 32
CBSE 2025	Series 55-4	Set 3	Question 31

• Step 1: Stating the fundamental formula / law statement (+1 Mark)
• Step 2: Intermediate mathematical substitution or proof steps (+1 Mark)
• Step 3: Correct final value or conclusion with mandatory SI units (+1 Mark)