(a) (i) Explain with the help of a labelled ray diagram the formation of final image by an astronomical telescope at infinity. Write the expression for its magnifying power. (ii) The total magnification produced by a compound microscope is 20. The magnification produced by the eyepiece is 5. When the microscope is focussed on a certain object, the distance between the objective and eyepiece is observed to be $14\text{ cm}$. Calculate the focal lengths of the objective and the eyepiece. (Given that the least distance of distinct vision $= 25\text{ cm}$) OR (b) (i) Two coherent light waves, each of intensity $I_0$ superpose each other and produce interference pattern on a screen. Obtain the expression for the resultant intensity at a point where the phase difference between the waves is $\phi$. Write its maximum and minimum possible values. (ii) In a single slit diffraction experiment, the aperture of the slit is $3\text{ mm}$ and the separation between the slit and the screen is $1\cdot5\text{ m}$. A monochromatic light of wavelength $600\text{ nm}$ is normally incident on the slit. Calculate the distance of (I) first order minimum, and (II) second order maximum, from the centre of the screen.

Year	Paper Code	Set	Position
CBSE 2025	Series 55-7	Set 1	Question 33
CBSE 2025	Series 55-7	Set 2	Question 31
CBSE 2025	Series 55-7	Set 3	Question 32

• 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)