Geometrical Optics – 100 Basic MCQs with Answers & Explanations

100 Important Basic MCQs (Level -1) on Geometrical Optics, Physics (Unit-Wise MCQs Practice):
👉Physics MCQs Hub – Unit wise Physics MCQs Practice (Main-Page)👈
Whether you are preparing for board examinations, chapter tests, college assessments, or competitive entrance exams (MDCAT, ECAT, NUST, PIEAS, GIKI, UET, FAST, and other engineering or medical admission tests), this comprehensive MCQ collection is designed to help you master Unit 16 – Geometrical Optics. The questions progress from basic concepts to advanced numerical problems and higher-order thinking skills, ensuring complete and systematic exam preparation.
This chapter-wise MCQ collection includes:
100 Basic MCQs Level -1 (1 - 100) Reflection, refraction, mirrors, lenses, prisms, refractive index, optical instruments, and vision defects.
100 Advanced & Numerical MCQs (101 -200): Mirror and lens formulae, magnification, lens power, Snell's law, prism calculations, critical angle, total internal reflection, and numerical applications.
50 Higher-Order Thinking Skills (HOTS) MCQs 201 - 250): Analytical reasoning, conceptual understanding, Board-inspired questions, practical applications, and competitive exam-level problems.
50 Challenging MCQs Quiz with Answers: A carefully selected mix of conceptual, numerical, and HOTS questions for quick revision, self-assessment, and complete exam preparation.
Key Topics Covered
Reflection and refraction of light
Plane, concave, and convex mirrors
Convex and concave lenses
Mirror and lens formulae
Magnification and lens power
Refractive index and Snell's law
Apparent depth, prisms, and dispersion
Critical angle and total internal reflection
Optical fibres and optical instruments
Human eye and common vision defects
Every MCQ includes the correct answer with a clear concept-based explanation to strengthen understanding, improve problem-solving skills, and build confidence in objective-type questions.
With 250 carefully selected MCQs arranged into 100 Basic, 100 Advanced & Numerical, and 50 HOTS questions, plus a 50-question Challenging MCQs Quiz, this all-in-one question bank provides complete preparation for Unit 16 – Geometrical Optics and helps students excel in both board examinations and competitive entrance tests.
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Geometrical Optics MCQs Level 1 – 100 Basic MCQs (1 – 100)

MCQ No. 1

Geometrical optics is the branch of physics that studies:

a. The wave nature of light only

b. The behavior of light as rays

c. The quantum nature of light

d. The electrical properties of light

Correct answer: b

Explanation: Geometrical optics, also known as ray optics, treats light as straight-line rays and explains reflection, refraction, and image formation without considering the wave nature of light.

MCQ No. 2

The basic assumption in geometrical optics is that light:

a. Travels in circles

b. Travels in straight lines in a homogeneous medium

c. Travels only through air

d. Always bends around obstacles

Correct answer: b

Explanation: In a uniform (homogeneous) transparent medium, light is assumed to travel in straight lines. This principle is known as the rectilinear propagation of light.

MCQ No. 3

Which phenomenon provides evidence that light travels in straight lines?

a. Reflection

b. Diffraction

c. Formation of shadows

d. Polarization

Correct answer: c

Explanation: Shadows are formed because light travels in straight lines and cannot bend around opaque objects under ordinary conditions.

MCQ No. 4

A narrow beam representing the direction of light propagation is called:

a. Wavefront

b. Optical axis

c. Light ray

d. Photon

Correct answer: c

Explanation: A light ray is an imaginary line that indicates the direction in which light energy propagates.

MCQ No. 5

A collection of many light rays is called:

a. Beam of light

b. Image

c. Spectrum

d. Reflection

Correct answer: a

Explanation: A beam consists of numerous light rays traveling together. It may be parallel, convergent, or divergent.

MCQ No. 6

A medium that allows almost all incident light to pass through it is called:

a. Opaque

b. Translucent

c. Transparent

d. Reflective

Correct answer: c

Explanation: Transparent materials such as clean glass and pure water transmit most of the light falling on them.

MCQ No. 7

A medium that allows only part of the incident light to pass through is:

a. Transparent

b. Opaque

c. Translucent

d. Vacuum

Correct answer: c

Explanation: Translucent materials scatter transmitted light, allowing only partial visibility through them.

MCQ No. 8

An object through which light cannot pass is called:

a. Transparent

b. Opaque

c. Translucent

d. Refractive

Correct answer: b

Explanation: Opaque materials block light completely, producing shadows behind them.

MCQ No. 9

The bouncing back of light from a surface is called:

a. Refraction

b. Reflection

c. Diffraction

d. Dispersion

Correct answer: b

Explanation: Reflection occurs when light returns to the same medium after striking a surface.

MCQ No. 10

The first law of reflection states that:

a. Angle of incidence is always 90°

b. The incident ray, reflected ray, and the normal lie in the same plane

c. Light bends toward the normal

d. Reflection occurs only from mirrors

Correct answer: b

Explanation: The incident ray, reflected ray, and normal at the point of incidence always lie in one plane.

MCQ No. 11

The second law of reflection states that:

a. The reflected ray is always brighter

b. Angle of incidence equals angle of reflection

c. Angle of incidence is twice the angle of reflection

d. Reflection occurs only on smooth surfaces

Correct answer: b

Explanation: The angle between the incident ray and the normal equals the angle between the reflected ray and the normal.

MCQ No. 12

The angle of incidence is measured between the:

a. Incident ray and mirror surface

b. Incident ray and reflected ray

c. Incident ray and normal

d. Reflected ray and mirror surface

Correct answer: c

Explanation: Angles in reflection are always measured from the normal drawn perpendicular to the reflecting surface.

MCQ No. 13

The line drawn perpendicular to the reflecting surface at the point of incidence is called the:

a. Principal axis

b. Radius

c. Normal

d. Optical center

Correct answer: c

Explanation: The normal is an imaginary line used to measure the angles of incidence and reflection.

MCQ No. 14

Reflection from a smooth polished surface is called:

a. Diffuse reflection

b. Irregular reflection

c. Regular reflection

d. Total reflection

Correct answer: c

Explanation: A smooth surface reflects parallel rays in one direction, producing regular reflection and clear images.

MCQ No. 15

Reflection from a rough surface is known as:

a. Regular reflection

b. Specular reflection

c. Diffuse reflection

d. Total internal reflection

Correct answer: c

Explanation: Rough surfaces scatter reflected light in different directions, producing diffuse reflection.

MCQ No. 16

A plane mirror forms an image that is:

a. Real and inverted

b. Virtual and erect

c. Real and diminished

d. Real and magnified

Correct answer: b

Explanation: Images formed by plane mirrors are always virtual, upright (erect), and of the same size as the object.

MCQ No. 17

The image formed by a plane mirror is:

a. Larger than the object

b. Smaller than the object

c. Equal in size to the object

d. Sometimes larger and sometimes smaller

Correct answer: c

Explanation: A plane mirror always produces an image having the same dimensions as the object.

MCQ No. 18

The distance of the image behind a plane mirror is:

a. Twice the object distance

b. Equal to the object distance

c. Half the object distance

d. Independent of object distance

Correct answer: b

Explanation: In a plane mirror, the image forms behind the mirror at the same perpendicular distance as the object is in front.

MCQ No. 19

The image formed by a plane mirror is:

a. Real

b. Virtual

c. Inverted

d. Projected on a screen

Correct answer: b

Explanation: A virtual image cannot be obtained on a screen because light rays only appear to come from the image.

MCQ No. 20

The phenomenon in which the left side of an object appears as the right side in a mirror is called:

a. Reflection

b. Dispersion

c. Lateral inversion

d. Refraction

Correct answer: c

Explanation: Plane mirrors reverse the image sideways, producing lateral inversion.

MCQ No. 21

A person stands 3 m in front of a plane mirror. The image is formed:

a. 1.5 m behind the mirror

b. 3 m behind the mirror

c. 6 m behind the mirror

d. At the mirror surface

Correct answer: b

Explanation: The image distance in a plane mirror is equal to the object distance. Therefore, the image forms 3 m behind the mirror.

MCQ No. 22

The distance between a person and his image in a plane mirror is 8 m. The person is standing:

a. 2 m from the mirror

b. 4 m from the mirror

c. 6 m from the mirror

d. 8 m from the mirror

Correct answer: b

Explanation: The person-image separation is twice the object distance. Therefore, object distance = 8 ÷ 2 = 4 m.

MCQ No. 23

Which type of image can be obtained on a screen?

a. Virtual image

b. Plane mirror image

c. Real image

d. Lateral image

Correct answer: c

Explanation: Only real images are formed by the actual convergence of light rays and can be projected onto a screen.

MCQ No. 24

Which of the following is NOT a characteristic of the image formed by a plane mirror?

a. Virtual

b. Erect

c. Same size as the object

d. Real

Correct answer: d

Explanation: A plane mirror never forms a real image. Its image is always virtual, erect, laterally inverted, and equal in size to the object.

MCQ No. 25

Which statement best explains why geometrical optics is widely used in designing optical instruments?

a. It treats light as electric current.

b. It simplifies the analysis of light by representing it as rays.

c. It ignores reflection and refraction.

d. It explains only the color of light.

Correct answer: b

Explanation: Geometrical optics provides a simple yet highly effective model for analyzing the path of light rays through mirrors, lenses, prisms, and optical instruments, making it the foundation for designing many practical optical devices.

MCQ No. 26

When an object moves closer to a plane mirror, the image:

a. Moves away from the mirror

b. Also moves closer to the mirror by the same distance

c. Remains fixed

d. Disappears

Correct answer: b

Explanation: In a plane mirror, the image is always formed at the same distance behind the mirror as the object is in front. Therefore, when the object moves closer, the image also moves closer by the same amount.

MCQ No. 27

If a plane mirror is moved 2 cm towards a stationary object, the image shifts by:

a. 1 cm

b. 2 cm

c. 4 cm

d. 6 cm

Correct answer: c

Explanation: When a plane mirror moves by a distance d, the image shifts by 2d. Therefore, a 2 cm movement of the mirror causes the image to move 4 cm.

MCQ No. 28

Two plane mirrors are placed parallel to each other. The number of images formed is:

a. One

b. Two

c. Four

d. Infinite

Correct answer: d

Explanation: Parallel plane mirrors repeatedly reflect images back and forth, producing an infinite number of images (ideally).

MCQ No. 29

Two plane mirrors are inclined at 90° to each other. The number of images formed is:

a. 2

b. 3

c. 4

d. Infinite

Correct answer: b

Explanation: The number of images formed by two inclined mirrors is given by $N=\frac{360^\circ}{\theta}-1$ when $\frac{360^\circ}{\theta}$ is an integer. For θ = 90°, $N=4-1=3$ .

MCQ No. 30

Two plane mirrors are inclined at 60°. The number of images produced is:

a. 3

b. 4

c. 5

d. 6

Correct answer: c

Explanation: For θ = 60°, $N=\frac{360^\circ}{60^\circ}-1=6-1=5$ . Thus, five images are formed.

MCQ No. 31

If two plane mirrors are inclined at 120°, the number of images formed is:

a. 2

b. 3

c. 4

d. 5

Correct answer: a

Explanation: $N=\frac{360^\circ}{120^\circ}-1=3-1=2$ . Therefore, two images are formed.

MCQ No. 32

Which property of a plane mirror makes it useful as a dressing mirror?

a. It forms real images.

b. It produces magnified images.

c. It forms erect images of the same size.

d. It changes the color of objects.

Correct answer: c

Explanation: A plane mirror forms a virtual, erect image equal in size to the object, making it ideal for everyday use.

MCQ No. 33

The minimum height of a plane mirror required to see the full image of a person is:

a. Equal to the person's height

b. Half of the person's height

c. One-third of the person's height

d. Double the person's height

Correct answer: b

Explanation: Only half the person's height is required because rays from the head and feet reflect in such a way that half the mirror is sufficient to view the entire body.

MCQ No. 34

The minimum size of a dressing mirror depends upon the:

a. Distance between the person and the mirror

b. Height of the person only

c. Width of the mirror

d. Brightness of the room

Correct answer: b

Explanation: The required mirror height is half the person's height and does not depend on how far the person stands from the mirror.

MCQ No. 35

Which of the following is an application of multiple reflections?

a. Magnifying glass

b. Kaleidoscope

c. Spectrometer

d. Microscope

Correct answer: b

Explanation: A kaleidoscope uses multiple reflections from inclined plane mirrors to produce beautiful symmetrical patterns.

MCQ No. 36

A spherical mirror whose reflecting surface is curved inward is called:

a. Convex mirror

b. Plane mirror

c. Concave mirror

d. Cylindrical mirror

Correct answer: c

Explanation: A concave mirror has its reflecting surface on the inner side of a spherical surface.

MCQ No. 37

A spherical mirror whose reflecting surface bulges outward is called:

a. Concave mirror

b. Convex mirror

c. Plane mirror

d. Parabolic mirror

Correct answer: b

Explanation: A convex mirror has its reflecting surface on the outer side of a sphere and always diverges incident light.

MCQ No. 38

The geometric center of the reflecting surface of a spherical mirror is known as the:

a. Focus

b. Pole

c. Radius

d. Vertex angle

Correct answer: b

Explanation: The pole is the midpoint of the reflecting surface and serves as the reference point for measuring distances.

MCQ No. 39

The center of the sphere from which a spherical mirror is formed is called the:

a. Optical center

b. Pole

c. Principal focus

d. Center of curvature

Correct answer: d

Explanation: The center of curvature is the center of the imaginary sphere of which the mirror is a part.

MCQ No. 40

The straight line joining the pole and the center of curvature is called the:

a. Radius

b. Principal axis

c. Optical axis

d. Normal

Correct answer: b

Explanation: The principal axis is the main reference line used in ray diagrams and image formation.

MCQ No. 41

The distance between the pole and the center of curvature is called the:

a. Focal length

b. Principal distance

c. Radius of curvature

d. Image distance

Correct answer: c

Explanation: The radius of curvature (R) is the radius of the sphere from which the mirror is formed.

MCQ No. 42

The point where rays parallel to the principal axis converge after reflection from a concave mirror is called the:

a. Pole

b. Principal focus

c. Center of curvature

d. Vertex

Correct answer: b

Explanation: The principal focus is the point where parallel rays actually meet after reflection from a concave mirror.

MCQ No. 43

For a convex mirror, rays parallel to the principal axis appear to diverge from the:

a. Pole

b. Center of curvature

c. Principal focus

d. Object

Correct answer: c

Explanation: A convex mirror has a virtual principal focus behind the mirror from which reflected rays appear to originate.

MCQ No. 44

The focal length of a spherical mirror is equal to:

a. Twice the radius of curvature

b. Half the radius of curvature

c. Three times the radius of curvature

d. Equal to the radius of curvature

Correct answer: b

Explanation: For every spherical mirror, the focal length is given by f = R/2.

MCQ No. 45

The radius of curvature of a spherical mirror having a focal length of 20 cm is:

a. 10 cm

b. 20 cm

c. 30 cm

d. 40 cm

Correct answer: d

Explanation: Since R = 2f, the radius of curvature is 2 × 20 = 40 cm.

MCQ No. 46

Which mirror is also known as a converging mirror?

a. Plane mirror

b. Convex mirror

c. Concave mirror

d. Cylindrical mirror

Correct answer: c

Explanation: A concave mirror converges parallel rays at its principal focus, hence it is called a converging mirror.

MCQ No. 47

Which mirror is also known as a diverging mirror?

a. Concave mirror

b. Convex mirror

c. Plane mirror

d. Parabolic mirror

Correct answer: b

Explanation: A convex mirror causes parallel rays to spread out after reflection, making it a diverging mirror.

MCQ No. 48

Which mirror always forms a virtual, erect, and diminished image?

a. Plane mirror

b. Concave mirror

c. Convex mirror

d. Parabolic mirror

Correct answer: c

Explanation: A convex mirror always produces a virtual, erect, and smaller image regardless of the object's position.

MCQ No. 49

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

a. At the pole

b. At the center of curvature

c. At the principal focus

d. Behind the mirror

Correct answer: c

Explanation: Rays coming from a very distant object are nearly parallel and converge at the principal focus after reflection.

MCQ No. 50

A dentist commonly uses a ________ to obtain a magnified view of a patient's teeth.

a. Plane mirror

b. Convex mirror

c. Concave mirror

d. Prism

Correct answer: c

Explanation: A concave mirror forms a magnified, upright virtual image when the object is placed between the pole and the principal focus. This property makes it useful for dental examinations and shaving mirrors.

MCQ No. 51

When an object is placed beyond the center of curvature of a concave mirror, the image is:

a. Virtual, erect, and magnified

b. Real, inverted, and diminished

c. Real, erect, and magnified

d. Virtual, inverted, and diminished

Correct answer: b

Explanation: When the object is beyond the center of curvature (C), a concave mirror forms a real, inverted, and diminished image between the focus (F) and the center of curvature (C).

MCQ No. 52

If an object is placed at the center of curvature of a concave mirror, the image formed is:

a. Virtual and magnified

b. Real, inverted, and of the same size

c. Virtual and diminished

d. Real and highly magnified

Correct answer: b

Explanation: At the center of curvature, the image is formed at the center of curvature itself. It is real, inverted, and equal in size to the object.

MCQ No. 53

When an object is placed between the center of curvature and the principal focus of a concave mirror, the image is:

a. Real, inverted, and magnified

b. Virtual and diminished

c. Real and diminished

d. Virtual and same size

Correct answer: a

Explanation: In this position, the image is formed beyond the center of curvature and is real, inverted, and enlarged.

MCQ No. 54

If an object is placed at the principal focus of a concave mirror, the reflected rays become:

a. Convergent

b. Divergent

c. Parallel

d. Perpendicular

Correct answer: c

Explanation: When the object is at the principal focus, the reflected rays become parallel to the principal axis, so the image is formed at infinity.

MCQ No. 55

When an object is placed between the pole and the principal focus of a concave mirror, the image formed is:

a. Real and inverted

b. Virtual, erect, and magnified

c. Real and diminished

d. Virtual and diminished

Correct answer: b

Explanation: A concave mirror acts like a magnifying mirror when the object lies between the pole and the focus, producing a virtual, erect, and enlarged image.

MCQ No. 56

A convex mirror always forms an image that is:

a. Real and magnified

b. Real and inverted

c. Virtual, erect, and diminished

d. Virtual and magnified

Correct answer: c

Explanation: Regardless of the object's position, a convex mirror always produces a virtual, upright, and diminished image behind the mirror.

MCQ No. 57

The mirror formula for spherical mirrors is:

a. $\frac{1}{u}+\frac{1}{v}=f$

b. $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

c. $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

d. $f=u+v$

Correct answer: c

Explanation: The mirror formula relates the focal length (f), object distance (u), and image distance (v) as 1/f = 1/u + 1/v using the appropriate sign convention.

MCQ No. 58

The linear magnification produced by a mirror is given by:

a. $m=\frac{v}{u}$

b. $m=\frac{u}{v}$

c. $m=\frac{f}{u}$

d. $m=\frac{R}{u}$

Correct answer: a

Explanation: Magnification is the ratio of image height to object height and is also equal to the ratio of image distance to object distance (with appropriate signs).

MCQ No. 59

A magnification greater than one indicates that the image is:

a. Diminished

b. Same size

c. Magnified

d. Invisible

Correct answer: c

Explanation: If the magnitude of magnification is greater than one, the image is larger than the object.

MCQ No. 60

According to the Cartesian sign convention, distances are measured from the:

a. Principal focus

b. Center of curvature

c. Pole of the mirror

d. Object

Correct answer: c

Explanation: In the Cartesian sign convention, all distances are measured from the pole of the mirror along the principal axis.

MCQ No. 61

The bending of light when it passes from one transparent medium to another is called:

a. Reflection

b. Dispersion

c. Refraction

d. Diffraction

Correct answer: c

Explanation: Refraction occurs because the speed of light changes when it enters a medium with a different optical density.

MCQ No. 62

Refraction takes place because the:

a. Frequency of light changes

b. Speed of light changes in different media

c. Wavelength always remains constant

d. Intensity of light changes

Correct answer: b

Explanation: The speed and wavelength of light change from one medium to another, causing the light ray to bend. The frequency remains unchanged.

MCQ No. 63

When light passes from air into glass, it bends:

a. Away from the normal

b. Towards the normal

c. Parallel to the surface

d. At an angle of 90°

Correct answer: b

Explanation: Glass is optically denser than air. Therefore, light slows down and bends toward the normal.

MCQ No. 64

When light travels from glass into air, it bends:

a. Towards the normal

b. Away from the normal

c. Along the normal

d. It does not bend

Correct answer: b

Explanation: As light enters a less dense medium, its speed increases, causing it to bend away from the normal.

MCQ No. 65

The angle between the incident ray and the normal is called the:

a. Angle of reflection

b. Angle of deviation

c. Angle of incidence

d. Critical angle

Correct answer: c

Explanation: The angle of incidence is measured between the incident ray and the normal at the point where the ray strikes the surface.

MCQ No. 66

The angle between the refracted ray and the normal is known as the:

a. Angle of incidence

b. Angle of reflection

c. Angle of refraction

d. Angle of deviation

Correct answer: c

Explanation: The angle of refraction is the angle made by the refracted ray with the normal inside the second medium.

MCQ No. 67

The law that governs the refraction of light is called:

a. Newton's Law

b. Ohm's Law

c. Snell's Law

d. Hooke's Law

Correct answer: c

Explanation: Snell's Law relates the angles of incidence and refraction with the refractive indices of the two media.

MCQ No. 68

According to Snell's Law:

a. $n_1\cos i=n_2\cos r$

b. $n_1\sin i=n_2\sin r$

c. $n_1\tan i=n_2\tan r$

d. $n_1i=n_2r$

Correct answer: b

Explanation: Snell's Law states that the product of the refractive index and the sine of the angle remains constant across the interface.

MCQ No. 69

The refractive index of a medium is defined as the ratio of:

a. Frequency in vacuum to frequency in medium

b. Speed of light in vacuum to speed in the medium

c. Speed in medium to speed in vacuum

d. Wavelength in medium to wavelength in vacuum

Correct answer: b

Explanation: The absolute refractive index is given by $n=\frac{c}{v}$ , where $c$ is the speed of light in vacuum and $v$ is its speed in the medium.

MCQ No. 70

The SI unit of refractive index is:

a. m/s

b. Meter

c. No unit

d. Newton

Correct answer: c

Explanation: Refractive index is a ratio of two speeds, making it a dimensionless quantity with no unit.

MCQ No. 71

If the refractive index of a medium increases, the speed of light in that medium:

a. Increases

b. Remains unchanged

c. Decreases

d. Becomes infinite

Correct answer: c

Explanation: Since $n=\frac{c}{v}$ , a larger refractive index corresponds to a lower speed of light in the medium.

MCQ No. 72

The refractive index of vacuum is:

a. 0

b. 0.5

c. 1

d. 1.5

Correct answer: c

Explanation: Vacuum is taken as the reference medium, so its refractive index is exactly 1.

MCQ No. 73

Which of the following has the highest refractive index?

a. Air

b. Water

c. Glass

d. Vacuum

Correct answer: c

Explanation: Among the given options, glass has the highest refractive index (approximately 1.5), so light travels slowest in glass.

MCQ No. 74

The frequency of light during refraction:

a. Increases

b. Decreases

c. Remains constant

d. Becomes zero

Correct answer: c

Explanation: During refraction, the frequency of light remains unchanged, while its speed and wavelength change.

MCQ No. 75

When light enters a denser medium, its wavelength:

a. Increases

b. Remains unchanged

c. Decreases

d. Becomes zero

Correct answer: c

Explanation: Since the speed of light decreases while the frequency remains constant, the wavelength also decreases according to $v=f\lambda$

MCQ No. 76

The phenomenon in which light is completely reflected back into the denser medium is called:

a. Diffraction

b. Dispersion

c. Total internal reflection

d. Polarization

Correct answer: c

Explanation: Total internal reflection (TIR) occurs when light traveling from a denser medium to a rarer medium strikes the boundary at an angle greater than the critical angle, causing all the light to be reflected back into the denser medium.

MCQ No. 77

Total internal reflection occurs when light travels:

a. From a rarer medium to a denser medium

b. From a denser medium to a rarer medium

c. Between two identical media

d. From air to water only

Correct answer: b

Explanation: One essential condition for total internal reflection is that light must travel from an optically denser medium to an optically rarer medium.

MCQ No. 78

The second condition required for total internal reflection is that the angle of incidence must be:

a. Equal to the angle of refraction

b. Less than the critical angle

c. Greater than the critical angle

d. Equal to 90°

Correct answer: c

Explanation: Total internal reflection occurs only when the angle of incidence exceeds the critical angle.

MCQ No. 79

The critical angle is the angle of incidence in the denser medium for which the angle of refraction is:

a. 0°

b. 45°

c. 60°

d. 90°

Correct answer: d

Explanation: At the critical angle, the refracted ray travels along the boundary between the two media, making an angle of 90° with the normal.

MCQ No. 80

Which of the following is NOT an application of total internal reflection?

a. Optical fibres

b. Endoscopes

c. Binocular prisms

d. Plane mirrors

Correct answer: d

Explanation: Optical fibres, endoscopes, and prism binoculars use total internal reflection, whereas an ordinary plane mirror works by reflection from a coated surface.

MCQ No. 81

Optical fibres transmit light mainly by:

a. Diffraction

b. Reflection

c. Total internal reflection

d. Dispersion

Correct answer: c

Explanation: Light repeatedly undergoes total internal reflection inside the core of an optical fibre, allowing it to travel long distances with minimal loss.

MCQ No. 82

The brilliant sparkle of a diamond is mainly due to:

a. Diffraction

b. Interference

c. Total internal reflection

d. Polarization

Correct answer: c

Explanation: Diamonds have a very high refractive index, resulting in a small critical angle and multiple total internal reflections that produce exceptional brilliance.

MCQ No. 83

A pencil partially immersed in water appears bent because of:

a. Reflection

b. Refraction

c. Diffraction

d. Polarization

Correct answer: b

Explanation: Light from the submerged portion of the pencil bends as it moves from water to air, making the pencil appear bent.

MCQ No. 84

The apparent depth of water is always:

a. Greater than the real depth

b. Equal to the real depth

c. Less than the real depth

d. Zero

Correct answer: c

Explanation: Due to refraction, objects under water appear closer to the surface than they actually are, making the apparent depth less than the real depth.

MCQ No. 85

The image of an object at the bottom of a swimming pool appears:

a. Deeper than its actual position

b. At the actual depth

c. Closer to the surface

d. Completely invisible

Correct answer: c

Explanation: Refraction causes underwater objects to appear raised, reducing their apparent depth.

MCQ No. 86

A lens that is thicker at the center than at the edges is called a:

a. Concave lens

b. Cylindrical lens

c. Convex lens

d. Plane lens

Correct answer: c

Explanation: A convex lens has greater thickness at its center and converges parallel rays of light.

MCQ No. 87

A lens that is thinner at the center than at the edges is known as a:

a. Convex lens

b. Concave lens

c. Plane mirror

d. Prism

Correct answer: b

Explanation: A concave lens diverges parallel rays and is thinner at the center than at the edges.

MCQ No. 88

A convex lens is also called a:

a. Diverging lens

b. Converging lens

c. Cylindrical lens

d. Reflecting lens

Correct answer: b

Explanation: A convex lens bends parallel rays toward a common point called the principal focus.

MCQ No. 89

A concave lens is commonly known as a:

a. Converging lens

b. Reflecting lens

c. Diverging lens

d. Optical prism

Correct answer: c

Explanation: A concave lens spreads out parallel rays, making it a diverging lens.

MCQ No. 90

The point through which a ray passes without deviation in a thin lens is called the:

a. Principal focus

b. Optical center

c. Pole

d. Center of curvature

Correct answer: b

Explanation: A ray passing through the optical center of a thin lens continues in the same direction without significant deviation.

MCQ No. 91

The formula for a thin lens is:

a. $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

b. $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

c. $f=u+v$

d. $v=uf$

Correct answer: b

Explanation: Using the Cartesian sign convention, the thin lens formula is 1/f = 1/v − 1/u, where u is the object distance and v is the image distance.

MCQ No. 92

The SI unit of the power of a lens is:

a. Watt

b. Joule

c. Dioptre

d. Tesla

Correct answer: c

Explanation: The power of a lens is measured in dioptres (D), where $P=\frac{1}{f}$ when the focal length is expressed in metres.

MCQ No. 93

The power of a lens is numerically equal to:

a. The radius of curvature

b. The reciprocal of its focal length in metres

c. Twice its focal length

d. The product of focal length and refractive index

Correct answer: b

Explanation: The power of a lens is defined as $P=\frac{1}{f}$ , where $f$ is measured in metres.

MCQ No. 94

The unit dioptre (D) is equal to:

a. $1\,\text{m}$

b. $1\,\text{m}^{-1}$

c. $1\,\text{cm}^{-1}$

d. $1\,\text{s}^{-1}$

Correct answer: b

Explanation: One dioptre is the power of a lens having a focal length of one metre, so $1\,\text{D}=1\,\text{m}^{-1}$ .

MCQ No. 95

A convex lens has:

a. Negative focal length

b. Positive focal length

c. Zero focal length

d. Infinite focal length

Correct answer: b

Explanation: According to the Cartesian sign convention, a convex (converging) lens has a positive focal length.

MCQ No. 96

A concave lens has:

a. Positive focal length

b. Zero focal length

c. Negative focal length

d. Infinite focal length

Correct answer: c

Explanation: Since a concave lens diverges light, its focal length is taken as negative.

MCQ No. 97

A prism is primarily used to:

a. Produce sound

b. Reflect all incident light

c. Refract and disperse light

d. Increase the speed of light

Correct answer: c

Explanation: A prism bends light by refraction and can separate white light into its constituent colours through dispersion.

MCQ No. 98

The splitting of white light into its constituent colours is called:

a. Reflection

b. Diffraction

c. Dispersion

d. Polarization

Correct answer: c

Explanation: Dispersion occurs because different colours of light are refracted by different amounts while passing through a prism.

MCQ No. 99

Which colour of visible light is deviated the least by a glass prism?

a. Violet

b. Blue

c. Green

d. Red

Correct answer: d

Explanation: Red light has the longest wavelength and the lowest refractive index in glass, so it undergoes the least deviation.

MCQ No. 100

Which colour of visible light is deviated the most by a glass prism?

a. Red

b. Yellow

c. Green

d. Violet

Correct answer: d

Explanation: Violet light has the shortest wavelength and experiences the greatest refractive index in glass, causing it to undergo the maximum deviation.

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