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Rajasthan Board Class 12 (RBSE) Ray Optics and Optical Instruments — practice questions

Explore 45 free Ray Optics and Optical Instruments questions in Rajasthan Board Class 12 (RBSE) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Ray Optics and Optical Instruments questions and exercises with answers

Showing questions 1–30 of 45.

Snell's law of refraction at the boundary between two media of refractive indices $n_1$ and $n_2$ statesRead the answer and worked solution →The relationship between the focal length $f$ and the radius of curvature $R$ for a SPHERICAL MIRROR isRead the answer and worked solution →The POWER of a lens (in diopters, D) is defined asRead the answer and worked solution →Two thin lenses of powers $+5\,\text{D}$ and $-3\,\text{D}$ are placed in CONTACT. The total power of the combination isRead the answer and worked solution →A converging lens of focal length $20\,\text{cm}$ produces a real image at $30\,\text{cm}$ from the lens. The object distance is closest toRead the answer and worked solution →When light travels from one medium to another, which property of the wave REMAINS UNCHANGED?Read the answer and worked solution →An object is placed at the FOCUS of a concave mirror ($u = f$, both negative). The image forms atRead the answer and worked solution →The phenomenon by which the apparent position of a star near the horizon appears slightly higher than its actual position is calledRead the answer and worked solution →The mirror equation relates u, v and f asRead the answer and worked solution →The power P of a lens of focal length f (in metres) is given byRead the answer and worked solution →An object is placed 30 cm from a concave mirror of focal length 20 cm. The image distance isRead the answer and worked solution →Refractive index of water with respect to air is 4/3. The critical angle for a water–air interface is approximatelyRead the answer and worked solution →A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 25 cm. The power of the combination (in dioptres) isRead the answer and worked solution →Light passes from air (n=1) into glass (n=1.5) at an incidence angle of 60°. Using Snell's law, the angle of refraction isRead the answer and worked solution →For a thin prism of small refracting angle A and refractive index n, the deviation δ is approximatelyRead the answer and worked solution →An astronomical telescope in normal adjustment has an objective of focal length 100 cm and an eyepiece of focal length 5 cm. Its angular magnification isRead the answer and worked solution →The apparent depth of an object lying at the bottom of a pool of water (n = 4/3) is, in terms of its real depth h,Read the answer and worked solution →A thin prism of refracting angle 5° is made of glass with n = 1.5. The deviation δ of a light ray passing through it is approximatelyRead the answer and worked solution →Two thin convex lenses, each of focal length 20 cm, are placed coaxially 10 cm apart in air. The equivalent focal length of the combination isRead 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 →

Worked practice questions

Snell's law of refraction at the boundary between two media of refractive indices $n_1$ and $n_2$ states

  1. $n_1\sin\theta_1 = n_2\sin\theta_2$
  2. $n_1\cos\theta_1 = n_2\cos\theta_2$
  3. $n_1\tan\theta_1 = n_2\tan\theta_2$
  4. $n_1 + \theta_1 = n_2 + \theta_2$
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Correct answer: A. $n_1\sin\theta_1 = n_2\sin\theta_2$

1. Your syllabus: when a ray crosses from medium 1 to medium 2, the angles of incidence and refraction (both measured from the NORMAL) satisfy $n_1\sin\theta_1 = n_2\sin\theta_2$. 2. Consequence: when light enters a denser medium (higher $n$), it bends TOWARD the normal; entering rarer (lower $n$), it bends AWAY. 3. The refractive index $n = c/v$ measures how much slower light travels in the medium. 4. Options B, C, D have wrong trigonometric functions or wrong functional form — Snell's law has no derivation that produces cosines, tangents, or sums. _Source: syllabus Physics Part 2, Ch 9 "Ray Optics", §9.3 (Refraction, Eq. 9.4), p. 2–3._

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The relationship between the focal length $f$ and the radius of curvature $R$ for a SPHERICAL MIRROR is

  1. $f = 2R$
  2. $f = R$
  3. $f = R/2$
  4. $f = R^2/2$
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Correct answer: C. $f = R/2$

1. syllabus derives the focal-length / radius relation for a spherical mirror, for rays close to the principal axis (paraxial approximation). 2. The focal point lies at HALF the distance from the pole to the centre of curvature. 3. So $f = R/2$. The same relation holds for concave and convex mirrors (sign-aware). 4. Numerical example: a concave mirror with $R = 20\,\text{cm}$ has $f = 10\,\text{cm}$. 5. Options A and B are too large by factors of 4× and 2×. Option D has wrong dimensions. _Source: syllabus Physics Part 2, Ch 9, §9.2.4 (Focal length of spherical mirrors, Eq. 9.3), p. 4._

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The POWER of a lens (in diopters, D) is defined as

  1. $P = f$ (focal length in metres)
  2. $P = 1/f$ where $f$ is in centimetres
  3. $P = f^2$
  4. $P = 1/f$ where $f$ is in metres
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Correct answer: D. $P = 1/f$ where $f$ is in metres

1. syllabus defines lens power. 2. $P = 1/f$, where $f$ is the focal length expressed in METRES. 3. SI unit: diopter (D), defined as $1\,\text{D} = 1\,\text{m}^{-1}$. 4. Higher power = shorter focal length = stronger converging (or diverging) action. 5. Sign: positive $P$ for converging lens (converging combination), negative $P$ for diverging. 6. Example: a lens with $f = +50\,\text{cm} = +0.5\,\text{m}$ has $P = +2\,\text{D}$. A diverging lens with $f = -25\,\text{cm}$ has $P = -4\,\text{D}$. 7. Options A and C have wrong forms. Option D uses cm instead of m, which gives a number 100× too large. _Source: syllabus Physics Part 2, Ch 9, §9.6.3 (Power of a Lens, Eq. 9.21), p. 18._

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