Class 12 Ray Optics and Optical Instruments Mock Test (CBSE)

Topics in Ray Optics and Optical Instruments

• Reflection of light by spherical mirrors
• Refraction
• Total internal reflection
• Refraction at spherical surfaces and by lenses
• Lens maker's formula
• Power of a lens
• Combination of thin lenses in contact
• Refraction through a prism
• Optical instruments: microscope and telescope

Ray Optics and Optical Instruments practice questions with answers

1. Q1Multiple choice·1 mark
   A ray of light passes through an equilateral glass prism. If the angle of incidence and the angle of emergence are each equal to $40^\circ$, the angle of deviation is:

   1. (a)$80^\circ$
   2. (b)$20^\circ$
   3. (c)$40^\circ$
   4. (d)$60^\circ$
   Show answer and step marks

   1. Correct option: (b) $20^\circ$+1

   Answer: (b)
2. Q2Multiple choice·1 mark
   Two thin lenses of power $+4\text{ D}$ and $-2\text{ D}$ are placed in contact coaxially. The focal length of the combination is:

   1. (a)$+25\text{ cm}$
   2. (b)$+50\text{ cm}$
   3. (c)$-50\text{ cm}$
   4. (d)$+200\text{ cm}$
   Show answer and step marks

   1. Correct option: (b) $+50\text{ cm}$+1

   Answer: (b)
3. Q3Short answer·3 marks
   An object of height $3.0\text{ cm}$ is placed at a distance of $18\text{ cm}$ in front of a concave mirror of focal length $12\text{ cm}$. (a) Determine the position of the image formed. (b) Find the size and nature of the image.
   Show answer and step marks

   1. Using mirror formula $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$ with sign convention ($f = -12\text{ cm}$, $u = -18\text{ cm}$), substitute the values.+1
   2. Calculate the image distance: $\frac{1}{v} = \frac{1}{-12} - \frac{1}{-18} = -\frac{1}{36}$, giving $v = -36\text{ cm}$ (image is formed $36\text{ cm}$ in front of the mirror).+1
   3. Magnification $m = -\frac{v}{u} = -\frac{-36}{-18} = -2$, so $h' = m h = (-2) \times 3.0\text{ cm} = -6.0\text{ cm}$: the image is $6.0\text{ cm}$ tall.+0.5
   4. Nature: real and inverted (negative $v$ and negative $m$), and magnified.+0.5

   Answer: (a) $v = -36\text{ cm}$ (36 cm in front of the mirror). (b) Size $6.0\text{ cm}$; real, inverted and magnified.

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