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MP Board Class 12 (MPBSE) Optics — practice questions

Explore 31 free Optics questions in MP Board Class 12 (MPBSE) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Optics questions and exercises with answers

Showing questions 1–30 of 31.

The critical angle for total internal reflection at a glass-air interface is $42^\circ$. The refractive index of the glass is approximately:Read the answer and worked solution →An object is placed $30\,\text{cm}$ in front of a concave mirror of focal length $20\,\text{cm}$. The image distance from the mirror is:Read the answer and worked solution →Two plane mirrors are inclined at an angle of $60^\circ$. The number of images of a point object placed between them is:Read the answer and worked solution →A convex mirror always forms an image of a real object that is:Read the answer and worked solution →A point source of light is placed at the origin in an isotropic medium. The wavefronts associated with the light are:Read the answer and worked solution →Cartesian sign convention: positive or negative?Read the answer and worked solution →True or false: the sign conventionRead the answer and worked solution →Complete the condition for total internal reflectionRead the answer and worked solution →Tap every example of total internal reflectionRead the answer and worked solution →Critical angleRead the answer and worked solution →True or false: optical fibresRead the answer and worked solution →Match each formula to what it describesRead the answer and worked solution →Converging or diverging?Read the answer and worked solution →Complete the definition of lens powerRead the answer and worked solution →Lenses in contactRead the answer and worked solution →Order the steps: solve a mirror problemRead the answer and worked solution →Assertion and reasonRead the answer and worked solution →Match each instrument to its magnifying powerRead the answer and worked solution →True or false: optical instrumentsRead the answer and worked solution →Which instrument does this belong to?Read the answer and worked solution →Two are true, one is notRead the answer and worked solution →Three of these are wrong. Find the one that holds.Read the answer and worked solution →Tap every statement true of refractionRead the answer and worked solution →Complete the prism relationRead the answer and worked solution →Flip and pair: symbol with meaningRead the answer and worked solution →Spot the one that does not belongRead the answer and worked solution →Reading the laws backRead the answer and worked solution →Order the reasoning: why an optical fibre worksRead the answer and worked solution →True or false: mirrors and lensesRead the answer and worked solution →Assertion and reason: instrumentsRead the answer and worked solution →

Worked practice questions

The critical angle for total internal reflection at a glass-air interface is $42^\circ$. The refractive index of the glass is approximately:

  1. $1.33$
  2. $1.41$
  3. $1.49$
  4. $2.42$
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Correct answer: C. $1.49$

For total internal reflection at a denser-to-rarer interface, $\mu = \dfrac{1}{\sin C}$. With $C = 42^\circ$, $\sin 42^\circ \approx 0.669$, so $\mu = 1/0.669 \approx 1.49$, which matches typical crown glass. **Option A is water and option D is diamond.**

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An object is placed $30\,\text{cm}$ in front of a concave mirror of focal length $20\,\text{cm}$. The image distance from the mirror is:

  1. $+12\,\text{cm}$
  2. $-60\,\text{cm}$
  3. $+60\,\text{cm}$
  4. $-12\,\text{cm}$
Show answer and solution

Correct answer: B. $-60\,\text{cm}$

Using the standard sign convention, $u = -30\,\text{cm}$ and $f = -20\,\text{cm}$ for a concave mirror. The mirror formula $\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}$ gives $\dfrac{1}{v} = \dfrac{1}{-20} - \dfrac{1}{-30} = -\dfrac{1}{60}$, so $v = -60\,\text{cm}$. The negative sign indicates the image is real and on the same side as the object, $60\,\text{cm}$ in front of the mirror.

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Two plane mirrors are inclined at an angle of $60^\circ$. The number of images of a point object placed between them is:

  1. $3$
  2. $4$
  3. $5$
  4. $6$
Show answer and solution

Correct answer: C. $5$

When $360^\circ/\theta$ is an integer, the number of images is $n = \dfrac{360^\circ}{\theta} - 1$. Here $360^\circ/60^\circ = 6$, an integer, so $n = 6 - 1 = 5$.

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