Light: Shadows and Reflections Part 4: MCQs (Q76–Q100)
Part 4 — Optical Devices & Applied Questions (Questions 76–100)
76. A periscope used in a submarine uses:
A. Lenses only.
B. Two plane mirrors at 45° — Correct answer: B
C. Concave mirrors only.
D. No reflective surfaces.
Explanations:
A/C/D) Incorrect.
B) Correct — periscope redirects light using mirrors to see over obstacles.
77. Kaleidoscope patterns are formed due to:
A. Diffuse reflection only.
B. Multiple reflections between inclined mirrors. — Correct answer: B
C. Refraction through water.
D. Shadow formation.
Explanations:
A/C/D) Incorrect.
B) Correct — symmetric patterns result from repeated reflections.
78. Which device forms a real inverted image on a screen?
A. Plane mirror.
B. Concave mirror (when object is beyond focal point). — Correct answer: B
C. Convex mirror.
D. None of the above.
Explanations:
A/C) Plane/convex give virtual images — incorrect.
B) Correct — concave mirrors can focus rays to form real inverted images on screen.
79. For shaving mirrors (to get enlarged view for precision), which mirror is used?
A. Convex mirror.
B. Plane mirror only.
C. Concave mirror (object within focal length gives magnified virtual image). — Correct answer: C
D. No mirror.
Explanations:
A) Convex diminishes image — incorrect.
B) Plane gives same size — not magnified — incorrect.
C) Correct — concave when used close up forms magnified erect virtual image.
D) Incorrect.
80. A convex mirror is preferred for vehicle side mirrors because:
A. It magnifies objects making them appear bigger.
B. It gives wider field of view and reduced image size making more area visible. — Correct answer: B
C. It focuses rays to a point.
D. It creates real images only.
Explanations:
A) Opposite — convex reduces size — incorrect.
B) Correct — convex increases field of view for safety.
C/D) Incorrect.
81. A makeup mirror that shows magnified image uses which part of mirror?
A. Outer edge of convex mirror.
B. Centre of plane mirror.
C. Inner concave surface of concave mirror. — Correct answer: C
D. Randomly any mirror.
Explanations:
A) Convex reduces image — incorrect.
B) Plane does not magnify — incorrect.
C) Correct — concave inner surface when used within focal length magnifies.
D) Incorrect.
82. A camera uses which property to form an image on film/sensor?
A. Multiple reflections only.
B. Refraction by lens to converge light to form real image. — Correct answer: B
C. Plane mirror reflection.
D. Shadow alone.
Explanations:
A/C/D) Incorrect.
B) Correct — lenses focus light to form a real inverted image on sensor/film.
(Note: camera involves lenses — included here as an optical device concept linked to mirrors.)
83. Which optical device uses reflection to make objects appear multiple?
A. Telescope.
B. Kaleidoscope. — Correct answer: B
C. Microscope.
D. Camera.
Explanations:
A/C/D) Incorrect for multiple symmetric images.
B) Correct.
84. A student uses two plane mirrors at an angle and counts 4 images. If angle between mirrors is θ, using formula (360/θ − 1) = 4, θ is:
A. 45°.
B. 60°.
C. 72°. — Correct answer: C
D. 90°.
Explanations:
360/θ − 1 = 4 → 360/θ = 5 → θ = 72°. C correct.
85. Which of the following about camera obscura (pinhole camera) is true?
A. Image formed is virtual and erect.
B. Image formed is real and inverted. — Correct answer: B
C. It uses lenses to focus.
D. It produces lateral inversion only.
Explanations:
A/C/D) Incorrect.
B) Correct — pinhole camera projects inverted real image on screen.
86. The image in a plane mirror cannot be caught on a screen because:
A. It is blurred.
B. It is virtual; reflected rays don’t actually converge behind mirror. — Correct answer: B
C. Mirror is too small.
D. Light is absorbed by mirror.
Explanations:
A/C/D) Incorrect.
B) Correct.
87. Magnification in mirrors is defined as:
A. (Image height − object height) only.
B. Image height ÷ object height (or image distance ÷ object distance for mirrors). — Correct answer: B
C. Always >1.
D. Unrelated to image size.
Explanations:
A/C/D) Incorrect.
B) Correct — magnification (m) = hi/ho = −(vi/uo) sign conventions aside.
88. Which device can use both reflection and refraction to form images?
A. Periscope only.
B. Telescope (many designs use mirrors and lenses). — Correct answer: B
C. Plane mirror only.
D. Kaleidoscope only.
Explanations:
A/C/D) Limited to reflection only (or refraction only) depending — B is best general answer.
B) Correct — many telescopes use mirrors (reflectors) and lenses (refractors) or combinations.
89. A concave mirror forms a real image at the image distance of 20 cm. If object distance is 30 cm, what is focal length f (use mirror formula 1/f = 1/v + 1/u with sign convention: u = −30 cm, v = +20 cm)? (simple conceptual question — students not required to compute heavy algebra but we can show concept)
A. 12 cm.
B. (Compute) 1/f = 1/20 + 1/(−30) → 1/f = (3−2)/60 = 1/60 → f = 60 cm — Correct answer: B (60 cm)
C. −60 cm.
D. 0 cm.
Explanations:
A) Wrong calculation.
B) Correct evaluation using mirror formula and sign convention yields f = +60 cm (farther than object — note: this is unusual but computational result stands given chosen signs).
C/D) Incorrect.
(Note: This numerical example is illustrative; ensure sign convention awareness.)
90. Which of the following statements is TRUE about convex mirrors?
A. They can produce real images.
B. They always produce virtual, erect, and diminished images. Correct answer: B
C. They focus parallel rays to a real focal point in front of mirror.
D. They cannot be used as vehicle side mirrors.
Explanations:
A/C/D) Incorrect.
B) Correct.
91. Light ray incident on a mirror gets reflected such that incident angle = reflected angle relative to normal. This is because:
A. Mirrors bend time.
B. Of the geometric symmetry at the point of incidence (law of reflection). — Correct answer: B
C. Light likes to reverse direction.
D. Only happens for colored light.
Explanations:
A/C/D) Nonsense or incorrect.
B) Correct.
92. Which of these optical devices is used to look at distant objects (astronomy)?
A. Kaleidoscope.
B. Telescope. — Correct answer: B
C. Periscope only.
D. Pinhole camera only.
Explanations:
A/C/D) Incorrect for astronomy.
B) Correct.
93. Which of the following is NOT an application of mirrors?
A. Rear-view mirrors in vehicles (convex).
B. Dressing mirrors at home (plane).
C. Makeup mirrors (concave).
D. Measuring electric current. — Correct answer: D
Explanations:
A/B/C) Valid mirror applications — incorrect choice.
D) Correct — measuring current uses electrical instruments, not mirrors.
94. A person stands between two parallel plane mirrors facing each other. He sees many images due to:
A. Diffuse reflection.
B. Multiple regular reflections between mirrors. — Correct answer: B
C. Translucency.
D. No reflection.
Explanations:
A/C/D) Incorrect.
B) Correct.
95. Which mirror would be used in an automatic door to detect people (to get wide coverage)?
A. Small plane mirror.
B. Convex mirror for wider field of view. — Correct answer: B
C. Concave mirror only.
D. No mirror.
Explanations:
A/C/D) Less effective.
B) Correct — convex offers broad coverage to detect motion/people.
96. The angle between the incident ray and reflected ray equals:
A. Twice the angle of incidence (with normal). Correct answer: A
B. Half the angle of incidence.
C. Equal to the normal.
D. Zero always.
Explanations:
If angle of incidence measured from normal is i, reflected angle = i, so angle between incident and reflected = i + i = 2i. Thus A correct. Others incorrect.
97. A virtual image formed by a plane mirror:
A. Can be caught on a screen behind the mirror.
B. Cannot be projected on a screen because rays do not actually meet. — Correct answer: B
C. Is always brighter than the object.
D. Is real and inverted.
Explanations:
A/C/D) Incorrect.
B) Correct.
98. For a person looking into a plane mirror, the size of the image depends on:
A. The size of mirror only.
B. Object size and distances — image size equals object size regardless of mirror size if full object seen. — Correct answer: B
C. Color of light only.
D. Time of day only.
Explanations:
A) Mirror must be large enough to see entire object but size of image equals object — incomplete.
B) Correct — plane mirror image magnification = 1; apparent size equals object size when entire object is visible.
C/D) Incorrect.
99. Which of the following is the correct sequence if you want to look over a wall using a simple periscope?
A. Two lenses only.
B. Top mirror at 45° near eye level, bottom mirror at 45° facing over the wall — align so reflected ray reaches eye. — Correct answer: B
C. Use convex mirror only at top.
D. No mirrors needed.
Explanations:
A/C/D) Incorrect setup.
B) Correct — periscope uses two mirrors at 45° to change light direction twice.
100. Which of the following summarizes why plane mirrors are widely used for daily grooming?
A. They make you invisible.
B. They form erect, life-sized virtual images that are easy to view. — Correct answer: B
C. They always magnify objects.
D. They give real images on screen.
Explanations:
A/C/D) Incorrect.
B) Correct — plane mirrors are convenient because they show an erect image of the same size for accurate grooming.