Unit 16: Optics — Online MCQ Test
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Practice Unit 16: Optics with a free chapter-wise online MCQ test.
This chapter covers: Reflection of light spherical mirrors morror formula. Refraction of light at plane and spherical surfaces thin lens formula and lens maker formula. Total internal reflection and it....
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Unit 16: Optics — Important Questions & Answers
A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is μ, then the angle of incidence is nearly equal to:
- A. 2A
- B. μA
- C. A/2μ
- D. 2μA
Answer: B. μA
For a small angle prism, Snell's law at the first surface is sin(i) ≈ i = μr1. At the second surface, if it emerges normally, r2 = 0. Since A = r1 + r2, then r1 = A. Thus, i = μA.
For a small angle prism, Snell's law at the first surface is sin(i) ≈ i = μr1. At the second surface, if it emerges normally, r2 = 0. Since A = r1 + r2, then r1 = A. Thus, i = μA.
In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes:
- A. half
- B. four times
- C. one-fourth
- D. double
Answer: B. four times
Fringe width β = λD/d. If D' = 2D and d' = d/2, then β' = λ(2D)/(d/2) = 4 * (λD/d) = 4β.
Fringe width β = λD/d. If D' = 2D and d' = d/2, then β' = λ(2D)/(d/2) = 4 * (λD/d) = 4β.
The Brewster's angle i_b for an interface should be:
- A. 30° < i_b < 45°
- B. 45° < i_b < 90°
- C. i_b = 90°
- D. 0° < i_b < 30°
Answer: B. 45° < i_b < 90°
Brewster's angle is defined by tan(i_b) = n₂/n₁. For the transition from air to a denser medium (n > 1), tan(i_b) > 1, so i_b > 45°. Since the angle must be less than 90°, 45° < i_b < 90°.
Brewster's angle is defined by tan(i_b) = n₂/n₁. For the transition from air to a denser medium (n > 1), tan(i_b) > 1, so i_b > 45°. Since the angle must be less than 90°, 45° < i_b < 90°.
A microscope has an objective of focal length 2 cm, eyepiece of focal length 4 cm and the tube length of 40 cm. If the distance of distinct vision of eye is 25 cm, the magnification in the microscope is
- A. 100
- B. 125
- C. 150
- D. 250
Answer: B. 125
For a compound microscope, M = (L/fo) * (D/fe) = (40/2) * (25/4) = 20 * 6.25 = 125.
For a compound microscope, M = (L/fo) * (D/fe) = (40/2) * (25/4) = 20 * 6.25 = 125.
In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination and the total magnification in comparison to the power (p) and magnification (m) for each lens will be, respectively–
- A. 4p and 4m
- B. p/4 and 4m
- C. 4p and m/4
- D. p/4 and m/4
Answer: C. 4p and m/4
Total power P = p1+p2+p3+p4 = 4p. Total magnification M = m1*m2*m3*m4. If the setup is defined such that the combination acts as a lens, power increases while focal length/magnification properties adapt accordingly based on system constraints.
Total power P = p1+p2+p3+p4 = 4p. Total magnification M = m1*m2*m3*m4. If the setup is defined such that the combination acts as a lens, power increases while focal length/magnification properties adapt accordingly based on system constraints.
An unpolarized light beam in air is incident on a medium of refractive index 1.73 at Brewster's angle. Then-
- A. reflected light is completely polarized and the angle of reflection is close to 60°
- B. reflected light is partially polarized and the angle of reflection is close to 30°.
- C. both reflected and transmitted light are perfectly polarized with angles of reflection and refraction close to 60° and 30°, respectively.
- D. transmitted light is completely polarized with angle of refraction close to 30°
Answer: A. reflected light is completely polarized and the angle of reflection is close to 60°
Brewster's angle θB = tan⁻¹(μ). tan⁻¹(√3) = 60°. At this angle, the reflected ray is completely plane polarized, perpendicular to the plane of incidence.
Brewster's angle θB = tan⁻¹(μ). tan⁻¹(√3) = 60°. At this angle, the reflected ray is completely plane polarized, perpendicular to the plane of incidence.
An unpolarized light beam travelling in air is incident on a medium of refractive index 1.73 at Brewster's angle. Then-
- A. reflected light is completely polarized and the angle of reflection is close to 60°
- B. reflected light is partially polarized and the angle of reflection is close to 30°.
- C. both reflected and transmitted light are perfectly polarized with angles of reflection and refraction close to 60° and 30°, respectively.
- D. transmitted light is completely polarized with angle of refraction close to 30°
Answer: A. reflected light is completely polarized and the angle of reflection is close to 60°
At Brewster's angle (iB), tan(iB) = n. Since tan(60°) = √3 ≈ 1.732, iB = 60°. At this angle, the reflected light is completely plane-polarized perpendicular to the plane of incidence.
At Brewster's angle (iB), tan(iB) = n. Since tan(60°) = √3 ≈ 1.732, iB = 60°. At this angle, the reflected light is completely plane-polarized perpendicular to the plane of incidence.
The intensity of transmitted light when a polaroid sheet, placed between two crossed polarization at 22.5° from the polarization axis of one of the polaroid, is (I0 is the intensity of polarised light after passing through the first polaroid):
- A. I0 / 2
- B. I0 / 4
- C. I0 / 8
- D. I0 / 16
Answer: C. I0 / 8
I = I0 * cos^2(theta) * sin^2(theta) = I0 * (1/4) * sin^2(2*theta). For 22.5, 2*theta = 45. I = I0/4 * sin^2(45) = I0/4 * 1/2 = I0/8.
I = I0 * cos^2(theta) * sin^2(theta) = I0 * (1/4) * sin^2(2*theta). For 22.5, 2*theta = 45. I = I0/4 * sin^2(45) = I0/4 * 1/2 = I0/8.
An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
- A. large focal length and large diameter
- B. large focal length and small diameter
- C. small focal length and large diameter
- D. small focal length and small diameter
Answer: A. large focal length and large diameter
Angular magnification of an astronomical telescope = f₀/fₑ, so a large focal length of the objective gives large magnification. Angular resolution is given by θ = 1.22λ/D; a larger diameter D gives smaller θ (better resolution). Hence, objective with large focal length and large diameter is required.
Angular magnification of an astronomical telescope = f₀/fₑ, so a large focal length of the objective gives large magnification. Angular resolution is given by θ = 1.22λ/D; a larger diameter D gives smaller θ (better resolution). Hence, objective with large focal length and large diameter is required.
An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
- A. large focal length and small diameter
- B. large focal length and large diameter
- C. small focal length and large diameter
- D. small focal length and small diameter
Answer: B. large focal length and large diameter
Angular magnification of a telescope = f_objective / f_eyepiece, so large focal length of objective gives large magnification. Angular resolution = 1.22λ/D (limit of resolution), so larger diameter D gives better (smaller angle) resolution. Hence large focal length and large diameter objective is needed.
Angular magnification of a telescope = f_objective / f_eyepiece, so large focal length of objective gives large magnification. Angular resolution = 1.22λ/D (limit of resolution), so larger diameter D gives better (smaller angle) resolution. Hence large focal length and large diameter objective is needed.