📘 Light – Reflection and Refraction (Class 10 Science)

🔹 Part 3: Questions 51–75

Q51. The focal length of a concave mirror is 15 cm. Where should an object be placed to get a real and inverted image of the same size?

A) At the pole
B) At the focus
C) At the centre of curvature
D) Beyond centre of curvature

Correct Answer: C) At the centre of curvature

Explanation:

• A) Pole → No image formed here.
• B) Focus → Image at infinity.
• ✅ C) At C → Real, inverted, same size.
• D) Beyond C → Smaller image between C and F.

Q52. If an object is placed at the focus of a convex lens, the image formed is:

A) At infinity
B) At the optical centre
C) At 2F
D) Between F and 2F

Correct Answer: A) At infinity

Explanation:

• ✅ A) Rays parallel after refraction → Image at infinity.
• B, C, D → Not correct for object at focus.

Q53. Which type of mirror is used in solar cookers?

A) Convex mirror
B) Concave mirror
C) Plane mirror
D) Cylindrical mirror

Correct Answer: B) Concave mirror

Explanation:

• A) Convex → Spreads rays.
• ✅ B) Concave → Converges sunlight at focus, heating food.
• C, D → Not effective.

Q54. A convex mirror always forms images that are:

A) Real and inverted
B) Virtual and erect
C) Same size and real
D) Enlarged and real

Correct Answer: B) Virtual and erect

Explanation:

• ✅ B) Convex mirror → Virtual, erect, diminished, no matter object position.
• A, C, D → Not possible.

Q55. When an object is placed at infinity in front of a concave mirror, the image is formed at:

A) At focus, real and inverted
B) At centre of curvature, same size
C) At pole, virtual and erect
D) Between focus and centre of curvature

Correct Answer: A) At focus, real and inverted

Explanation:

• ✅ A) Parallel rays converge at focus.
• B, C, D → Not correct.

Q56. In which case is no refraction observed?

A) Light incident normally on boundary
B) From air to water at angle
C) From glass to air at angle
D) From air to diamond

Correct Answer: A) Light incident normally on boundary

Explanation:

• ✅ A) At 0° incidence → No bending, passes undeviated.
• B, C, D → Refraction occurs.

Q57. Which device uses refraction to form images?

A) Plane mirror
B) Concave mirror
C) Convex lens
D) Kaleidoscope

Correct Answer: C) Convex lens

Explanation:

• A, B → Reflection.
• ✅ C) Lens works on refraction.
• D → Reflection principle.

Q58. The mirror used in torches and headlights is:

A) Plane mirror
B) Convex mirror
C) Concave mirror
D) Cylindrical mirror

Correct Answer: C) Concave mirror

Explanation:

• ✅ C) Concave → Produces strong parallel beam.
• A, B, D → Not suitable.

Q59. The magnification produced by plane mirror is:

A) 0
B) +1
C) –1
D) Greater than 1

Correct Answer: B) +1

Explanation:

• ✅ B) Image is same size, virtual → Magnification = +1.
• A, C, D → Wrong.

Q60. The refractive index of glass with speed of light 2×10⁸ m/s is (c=3×10⁸ m/s):

A) 1.2
B) 1.33
C) 1.5
D) 2.0

Correct Answer: C) 1.5

Explanation:

• n = c/v = 3×10⁸ / 2×10⁸ = 1.5.
• ✅ C) Correct.

Q61. When object distance = focal length in convex lens, magnification is:

A) 0
B) ∞ (infinity)
C) 1
D) –1

Correct Answer: B) ∞ (infinity)

Explanation:

• ✅ B) Rays become parallel → Image at infinity → Infinite magnification.
• Others → Not true.

Q62. The nature of image formed by concave mirror when object is between F and P is:

A) Real, inverted, enlarged
B) Virtual, erect, enlarged
C) Virtual, erect, diminished
D) Real, inverted, diminished

Correct Answer: B) Virtual, erect, enlarged

Explanation:

• ✅ B) Concave near object → Enlarged, virtual.
• A, C, D → Wrong.

Q63. Which lens is used in spectacles for hypermetropia?

A) Concave lens
B) Convex lens
C) Cylindrical lens
D) Plano-concave lens

Correct Answer: B) Convex lens

Explanation:

• ✅ B) Convex lens → Converging lens corrects farsightedness.
• A) Concave → For myopia.
• C, D → Not for this defect.

Q64. The magnification produced by concave lens is always:

A) Positive and less than 1
B) Positive and greater than 1
C) Negative and less than 1
D) Zero

Correct Answer: A) Positive and less than 1

Explanation:

• ✅ A) Concave lens → Always virtual, erect, diminished → Magnification < 1, positive.

Q65. The image formed by convex mirror is always:

A) Real and inverted
B) Virtual, erect, diminished
C) Same size, real
D) Virtual, enlarged

Correct Answer: B) Virtual, erect, diminished

Explanation:

• ✅ B) Convex → Always virtual, erect, diminished.
• A, C, D → Wrong.

Q66. If object is at infinity, image formed by convex lens is:

A) At focus, real and inverted
B) At infinity, virtual
C) At 2F, same size
D) At pole, erect

Correct Answer: A) At focus, real and inverted

Explanation:

• ✅ A) Parallel rays converge at focus.

Q67. The bending of light around sharp edges is called:

A) Reflection
B) Refraction
C) Diffraction
D) Dispersion

Correct Answer: C) Diffraction

Explanation:

• ✅ C) Diffraction = Bending around edges.
• A, B, D → Other phenomena.

Q68. The formula for magnification (m) of a mirror is:

A) m = v/u
B) m = h₂/h₁
C) m = –v/u
D) Both A and C

Correct Answer: D) Both A and C

Explanation:

• ✅ D) m = –v/u (using distances) or m = h₂/h₁ (using sizes).

Q69. The speed of light in air is 3×10⁸ m/s and in glass is 2×10⁸ m/s. Refractive index is:

A) 1.0
B) 1.33
C) 1.5
D) 2.0

Correct Answer: C) 1.5

Explanation:

• n = c/v = 3/2 = 1.5.
• ✅ C.

Q70. The mirror used in shaving mirrors is:

A) Plane mirror
B) Concave mirror
C) Convex mirror
D) Parabolic mirror

Correct Answer: B) Concave mirror

Explanation:

• ✅ B) Concave → Enlarged, virtual image when face close.
• A, C, D → Not suitable.

Q71. The unit of focal length is:

A) Dioptre
B) Metre
C) Candela
D) Hertz

Correct Answer: B) Metre

Explanation:

• ✅ B) Focal length measured in metres.
• A) Power in Dioptre.
• C, D → Other units.

Q72. Which of the following always has a negative focal length?

A) Convex mirror
B) Concave mirror
C) Convex lens
D) Plano-convex lens

Correct Answer: A) Convex mirror

Explanation:

• ✅ A) Convex mirror → Diverging → Focal length negative.
• B, C, D → Converging (positive focal length).

Q73. The path of a ray through a glass slab emerges:

A) Parallel to incident ray but laterally displaced
B) Deviated towards normal
C) Undeviated without shift
D) Reflected back

Correct Answer: A) Parallel to incident ray but laterally displaced

Explanation:

• ✅ A) Glass slab causes lateral displacement, rays parallel.

Q74. The phenomenon of mirage is due to:

A) Total internal reflection
B) Diffraction
C) Dispersion
D) Reflection

Correct Answer: A) Total internal reflection

Explanation:

• ✅ A) Mirage in deserts due to TIR in hot air layers.

Q75. The refractive index of a medium depends on:

A) Nature of medium only
B) Wavelength of light only
C) Both medium and wavelength
D) Neither medium nor wavelength

Correct Answer: C) Both medium and wavelength

Explanation:

• ✅ C) Refractive index varies with medium and λ (colour dependence → dispersion).

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