Physics MCQ – Spherical Mirrors & Refraction (50 Qs — short explanations)
Q1. Uses of concave mirrors include which of the following?
a) As wall decoration
b) Concentrating sunlight in solar furnaces
c) As security mirrors in shops
d) In spectacles
Answer: Concentrating sunlight in solar furnaces.
Why correct: Concave mirrors converge parallel sunlight to a focus, allowing concentration of energy for heating. Why others wrong: (a) decoration is not a functional optical use; (c) security mirrors are usually convex for wide view; (d) spectacles do not use concave mirrors to concentrate light.
Q2. Concave mirrors are used in torches and headlights to get:
a) Scattered light
b) Powerful parallel beams of light
c) Diminished images
d) No reflection
Answer: Powerful parallel beams of light.
Why correct: A reflector shaped like a concave mirror takes light from a source at its focus and reflects it as nearly parallel rays, producing a beam. Why others wrong: (a) scattered light is opposite of aimed beam; (c) “diminished images” refers to image size, not beam formation; (d) mirrors always reflect, so “no reflection” is false.
Q3. Which mirror is often used as a shaving mirror to see a larger image?
a) Convex mirror
b) Plane mirror
c) Concave mirror
d) Cylindrical mirror
Answer: Concave mirror.
Why correct: When the object is within the focal length of a concave mirror, it produces an enlarged virtual erect image, useful for shaving. Why others wrong: (a) convex mirrors give diminished images; (b) plane mirrors give same-size images; (d) cylindrical mirror is not standard for this purpose.
Q4. Dentists use concave mirrors primarily to:
a) View a wider field
b) See enlarged images of teeth
c) See diminished images
d) Produce virtual images only
Answer: See enlarged images of teeth.
Why correct: Concave mirrors magnify nearby objects when the object is inside the focal length, helping inspection. Why others wrong: (a) wider field is a convex mirror property; (c) dentists want enlargement, not diminution; (d) concave mirrors can produce real or virtual images depending on object distance — the relevant use is virtual enlargement.
Q5. Large concave mirrors are mostly used in:
a) Car side mirrors
b) Solar furnaces
c) Home dressing tables
d) Periscopes
Answer: Solar furnaces.
Why correct: Large concave mirrors concentrate sunlight at a focus to produce high temperatures, as in solar furnaces. Why others wrong: (a) car side mirrors are convex; (c) dressing mirrors are typically plane or small concave but not large concentrators; (d) periscopes use plane mirrors/prisms, not large concave reflectors.
Q6. Convex mirrors are commonly used as:
a) Rear-view mirrors in vehicles
b) Shaving mirrors
c) Projectors
d) Magnifying glasses
Answer: Rear-view mirrors in vehicles.
Why correct: Convex mirrors provide a wide field of view and erect diminished images, ideal for seeing traffic behind. Why others wrong: (b) convex mirrors diminish rather than enlarge; (c) projectors require converging optics; (d) magnifying glasses are converging lenses, not convex mirrors.
Q7. Why are convex mirrors preferred as rear-view mirrors?
a) They form inverted images
b) They give enlarged images
c) They provide a wider field of view
d) They form no image
Answer: They provide a wider field of view.
Why correct: The outward curvature spreads reflected rays so the mirror shows a larger area behind the vehicle. Why others wrong: (a) convex images are erect, not inverted; (b) convex mirrors produce diminished, not enlarged, images; (d) mirrors always form images.
Q8. Compared to a plane mirror, a convex mirror gives:
a) A narrower field of view
b) A wider field of view
c) A real image
d) No image
Answer: A wider field of view.
Why correct: Curvature of a convex mirror lets it capture and reflect light from a broader angular range than a flat mirror. Why others wrong: (a) incorrect property; (c) convex mirrors produce virtual images; (d) incorrect — convex mirrors do form images.
Q9. Which of the following is TRUE about convex mirrors?
a) They always give an erect, diminished image
b) They always give inverted images
c) They concentrate sunlight
d) They give enlarged images for shaving
Answer: They always give an erect, diminished image.
Why correct: Geometry of convex surfaces causes reflections that form smaller (diminished), upright (erect), virtual images. Why others wrong: (b) convex images are not inverted; (c) convex mirrors diverge rays so cannot concentrate sunlight; (d) they reduce image size, so not suitable for shaving.
Q10. Define the principal focus of a concave mirror.
a) The point where parallel rays converge after reflection
b) The point where rays diverge before reflection
c) The center of the mirror surface
d) The point where the mirror is mounted
Answer: The point where parallel rays converge after reflection.
Why correct: By definition, the principal focus is where rays initially parallel to the principal axis meet after reflection from a concave mirror. Why others wrong: (b) divergent before reflection is not focus; (c) center of mirror is not the focal point; (d) mounting point is unrelated.
Q11. If the radius of curvature of a spherical mirror is 20 cm, its focal length is:
a) 10 cm
b) 20 cm
c) 40 cm
d) 5 cm
Answer: 10 cm.
Why correct: Focal length f = R/2 for spherical mirrors, so f = 20/2 = 10 cm. Why others wrong: (b) equals radius not half; (c) incorrect arithmetic; (d) too small relative to R/2.
Q12. Name a mirror that can give an erect and enlarged image of an object.
a) Concave mirror (when object is within focal length)
b) Convex mirror
c) Plane mirror
d) Spherical mirror that is plane
Answer: Concave mirror (when object is within focal length).
Why correct: If the object lies between pole and focus of a concave mirror, the mirror produces an erect, enlarged virtual image. Why others wrong: (b) convex gives erect but diminished images; (c) plane gives erect same-size images; (d) “spherical mirror that is plane” is contradictory.
Q13. Why do we prefer a convex mirror as a rear view mirror in vehicles?
a) Because it provides a wider field of view
b) Because it gives enlarged images
c) Because it concentrates light
d) Because it shows only a small area
Answer: Because it provides a wider field of view.
Why correct: Convex curvature increases the area visible to the driver, enhancing safety. Why others wrong: (b) convex images are diminished; (c) convex mirrors diverge rays, not concentrate; (d) opposite of true.
Q14. In sign conventions for spherical mirrors, focal length of a concave mirror is:
a) Positive
b) Negative
c) Zero
d) Variable
Answer: Negative.
Why correct: (Per the sign convention used in the supplied text) with object on the left and distances to the right positive, the focal point of a concave mirror lies to the left of the origin in that convention, so focal length is negative. Why others wrong: (a) positive contradicts the text’s chosen sign convention; (c) focal length is not zero; (d) focal length is a fixed value for a given mirror.
Q15. Focal length of a plane mirror is:
a) Infinite
b) Zero
c) Equal to radius of curvature
d) Always 50 cm
Answer: Infinite.
Why correct: Plane mirrors do not converge or diverge rays; their focal length is conceptually at infinity. Why others wrong: (b) zero would mean focus at mirror surface; (c) plane mirror has no curvature so R is infinite too; (d) arbitrary and incorrect.
Q16. Relationship between focal length (f) & radius of curvature (R):
a) f = R
b) f = 2R
c) R = 2f
d) f = R/3
Answer: R = 2f.
Why correct: For spherical mirrors the standard relation is R = 2f (or f = R/2). Why others wrong: (a)/(b)/(d) are incorrect algebraic relations.
Q17. Small area of a spherical mirror used for reflection is called:
a) Vertex
b) Aperture
c) Focus
d) Centre of curvature
Answer: Aperture.
Why correct: Aperture refers to the usable reflective area or opening size of the mirror. Why others wrong: (a) vertex/pole is a point, not area; (c) focus is a point where rays converge; (d) centre of curvature is a point in space.
Q18. Distance between pole & focus is:
a) Aperture
b) Radius
c) Focal length (f)
d) Principal axis
Answer: Focal length (f).
Why correct: Focal length is defined as distance from pole (mirror vertex) to the principal focus. Why others wrong: (a) aperture is area; (b) radius usually refers to radius of curvature; (d) principal axis is a line, not a distance.
Q19. Direction of incident light by convention is:
a) Towards the left
b) Towards the right
c) Upward
d) Arbitrary
Answer: Towards the left (by convention).
Why correct: The New Cartesian convention (used in the text) places the object to the left, so incident light travels from left to right and distances measured accordingly. Why others wrong: (b)/(c)/(d) contradict that stated convention.
Q20. Concave mirror forms an image at focus when object is:
a) Very far from mirror (at infinity)
b) At centre of curvature
c) At pole
d) Between focus & pole
Answer: Very far from mirror (at infinity).
Why correct: Rays from an object at infinity are practically parallel; a concave mirror reflects them to its focal point. Why others wrong: (b) yields image at center not focus; (c)/(d) produce different image locations.
Q21. Value of focal length if radius of curvature = 30 cm:
a) 5 cm
b) 10 cm
c) 15 cm
d) 20 cm
Answer: 15 cm.
Why correct: f = R/2, so 30/2 = 15 cm. Why others wrong: (a)/(b)/(d) are incorrect results.
Q22. Magnification > 1 indicates:
a) Diminished image
b) Enlarged image
c) Same size image
d) No image
Answer: Enlarged image.
Why correct: Magnification greater than one means image height is larger than object height. Why others wrong: (a) is magnification < 1; (c) corresponds to m = 1; (d) irrelevant.
Q23. If m = –1 (magnification), then image is:
a) Real, inverted and same size
b) Virtual, erect and same size
c) Real, erect and diminished
d) Virtual, inverted and enlarged
Answer: Real, inverted and same size.
Why correct: A magnification of –1 indicates image height equals object height but opposite sign denotes inversion; this occurs when object is at centre of curvature. Why others wrong: (b) sign would be +1; (c)/(d) mismatch sign and size.
Q24. A ray parallel to principal axis after reflection passes through:
a) Pole
b) Focus
c) Centre of curvature
d) Aperture
Answer: Focus.
Why correct: By mirror geometry, rays parallel to the principal axis reflect through the principal focus in concave mirrors. Why others wrong: (a)/(d) are not where parallel rays converge; (c) parallel rays don’t pass through centre of curvature after reflection.
Q25. Bending of light when it passes from one medium to another is called:
a) Reflection
b) Refraction
c) Dispersion
d) Scattering
Answer: Refraction.
Why correct: Refraction is the change of direction of light due to speed change across media. Why others wrong: (a) reflection is bounce off a surface; (c) dispersion separates colors; (d) scattering is random redirection by particles.
Q26. Laws of refraction are also known as:
a) Newton’s Laws
b) Snell’s Laws
c) Faraday’s Laws
d) Coulomb’s Laws
Answer: Snell’s Laws.
Why correct: Snell’s law gives the quantitative relation between angles of incidence and refraction for two media. Why others wrong: (a)/(c)/(d) refer to different physical laws unrelated to refraction.
Q27. Refractive index is defined as ratio of:
a) Speed of light in air to speed in medium
b) Speed of light in medium to speed in air
c) Height to image distance
d) Focal length to radius of curvature
Answer: Speed of light in air to speed in medium.
Why correct: Refractive index n = c (in vacuum/air) ÷ v (in medium); it quantifies slowing of light. Why others wrong: (b) is inverse of the definition; (c)/(d) irrelevant.
Q28. The phenomenon of a stick appearing bent in water is due to:
a) Reflection
b) Refraction
c) Dispersion
d) Scattering
Answer: Refraction.
Why correct: Light rays from the submerged part change direction at the air–water interface, making the stick appear displaced. Why others wrong: (a) would show mirror-like reversal; (c) color separation is not involved; (d) scattering causes diffused light, not apparent bending.
Q29. A light ray passing through optical center of lens:
a) Bends towards principal axis
b) Bends away from axis
c) Emerges without deviation
d) Merges into lens
Answer: Emerges without deviation.
Why correct: Rays through the optical center of a thin lens pass straight through since opposite refractions cancel. Why others wrong: (a)/(b) are typical for other ray paths; (d) is non-physical.
Q30. A concave lens always forms image that is:
a) Real and erect
b) Virtual, erect and diminished
c) Real and enlarged
d) Virtual and enlarged
Answer: Virtual, erect and diminished.
Why correct: Concave (diverging) lenses spread rays so the image is virtual, upright and smaller than object. Why others wrong: (a)/(c) are real-image cases from converging optics; (d) enlargement is not produced by diverging lenses.
Q31. Power of a lens is measured in:
a) Meter
b) Dioptre
c) Watt
d) Centimeter
Answer: Dioptre.
Why correct: Lens power = 1/f (in meters) and its SI unit is dioptre (m⁻¹). Why others wrong: (a)/(d) are distance units; (c) is power of energy, not optical power.
Q32. A lens that is thick at the center and thin at edges is called:
a) Concave lens
b) Convex lens
c) Plane lens
d) Cylindrical lens
Answer: Convex lens.
Why correct: Convex (converging) lenses bulge outward, thicker in center than at edges. Why others wrong: (a) concave is thinner at center; (c)/(d) are not descriptions matching bulged shape.
Q33. A real image can be obtained on:
a) Retina only
b) Screen
c) Paper only
d) Water surface
Answer: Screen.
Why correct: Real images are formed by converging rays and can be projected onto a screen. Why others wrong: (a) retina collects image in eye but is not the only place; (c) paper could receive light but “screen” is the standard projection surface; (d) water surface is not a reliable projection screen.
Q34. Path of a ray of light passing through the focus of a concave mirror after reflection:
a) Becomes parallel to principal axis
b) Passes through pole
c) Becomes circular
d) Goes randomly
Answer: Becomes parallel to principal axis.
Why correct: By reversibility of rays, a ray through the focus reflects out parallel to the principal axis. Why others wrong: (b)/(c)/(d) do not describe the standard ray-behavior for concave mirrors.
Q35. The center of a spherical mirror is known as:
a) Pole
b) Focus
c) Aperture
d) Centre of curvature
Answer: Centre of curvature.
Why correct: Centre of curvature is the center of the sphere of which the mirror is a part. Why others wrong: (a) pole is mirror vertex; (b) focus is point where parallel rays converge; (c) aperture is opening/area.
Q36. When light enters a denser medium from rarer medium, its speed:
a) Increases
b) Decreases
c) Remains same
d) Becomes zero
Answer: Decreases.
Why correct: Light slows down in a medium with higher refractive index, causing refraction. Why others wrong: (a) is opposite; (c)/(d) not physically correct for normal transparent media.
Q37. A convex mirror always forms:
a) Real and inverted image
b) Virtual and erect image
c) Real and erect image
d) No image at all
Answer: Virtual and erect image.
Why correct: Convex mirrors diverge rays so the image appears behind the mirror, virtual and upright. Why others wrong: (a)/(c) involve real images which convex mirrors do not form; (d) false.
Q38. Focal length of convex mirror is always:
a) Zero
b) Positive
c) Negative
d) Changing
Answer: Positive.
Why correct: Per the convention used in earlier text, convex mirror focal length (located to the right of pole) is taken positive. Why others wrong: (a) zero is not correct; (c)/(d) contradict the defined sign/location in that convention.
Q39. If image formed by a concave mirror is inverted and smaller than object, the object is placed:
a) At focus
b) Beyond centre of curvature
c) Between pole and focus
d) Very close to mirror
Answer: Beyond centre of curvature.
Why correct: When object lies beyond C (centre), the concave mirror produces a real, inverted, diminished image between C and F. Why others wrong: (a) at focus gives image at infinity; (c)/(d) give enlarged or virtual images, not diminished.
Q40. Which lens is used to correct short-sightedness (myopia)?
a) Convex lens
b) Concave lens
c) Bifocal lens
d) Cylindrical lens
Answer: Concave lens.
Why correct: Concave lenses diverge light so that images of distant objects are focused on the retina for myopic eyes. Why others wrong: (a) convex lens converges light (used for hypermetropia); (c)/(d) are specialized corrections, not primary myopia fix.
Q41. Which lens is used to correct long-sightedness (hypermetropia)?
a) Concave lens
b) Convex lens
c) Plane mirror
d) Spherical mirror
Answer: Convex lens.
Why correct: Convex lenses converge light, helping focus images of nearby objects onto the retina for hypermetropic eyes. Why others wrong: (a) diverging lens would worsen the condition; (c)/(d) are irrelevant.
Q42. Mirror that always produces virtual and erect images:
a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Both b and c
Answer: Both convex mirror and plane mirror.
Why correct: Plane mirrors always produce erect virtual images of same size; convex mirrors produce erect virtual diminished images. Why others wrong: (a) concave can produce real/inverted images depending on object distance.
Q43. The image formed by a plane mirror is:
a) Virtual, erect and same size
b) Real, erect and diminished
c) Virtual and inverted
d) Real and same size
Answer: Virtual, erect and same size.
Why correct: Plane mirror geometry produces an image behind the mirror equal in size and upright. Why others wrong: (b)/(d) real images do not occur with plane mirrors; (c) inversion does not occur.
Q44. Which of the following has the least refractive index?
a) Water
b) Air
c) Glass
d) Diamond
Answer: Air.
Why correct: Air is the least dense optical medium in the list, with refractive index ~1, lower than water, glass and diamond. Why others wrong: Water, glass, diamond have progressively higher refractive indices.
Q45. Eye defect that occurs due to weakening of ciliary muscles:
a) Myopia
b) Hypermetropia
c) Astigmatism
d) Presbyopia
Answer: Presbyopia.
Why correct: Presbyopia is age-related loss of accommodation because ciliary muscles weaken, reducing near focusing ability. Why others wrong: (a)/(b) are refractive errors due to eyeball shape; (c) is irregular corneal curvature, not ciliary weakness.
Q46. Lens used in a magnifying glass:
a) Concave lens
b) Convex lens
c) Prism
d) Plane mirror
Answer: Convex lens.
Why correct: A convex lens with short focal length produces an enlarged virtual image for close viewing. Why others wrong: (a) concave lenses diminish images; (c)/(d) do not magnify in the same way.
Q47. Mirror used in street lamps for better illumination:
a) Plane mirror
b) Convex mirror
c) Concave mirror
d) Parabolic mirror
Answer: Concave mirror.
Why correct: Concave reflectors concentrate and direct light to form stronger beams; parabolic/concave shapes are used — concave is the general correct term given choices. Why others wrong: (a) plane spreads light poorly; (b) convex diverges light; (d) parabolic is a specific type of concave but not listed as chosen option in earlier text.
Q48. When object is placed between focus and centre of curvature of concave mirror, image is:
a) Virtual and erect
b) Real, inverted and enlarged
c) Real and diminished
d) Behind the mirror
Answer: Real, inverted and enlarged.
Why correct: Objects between F and C produce real inverted images beyond F and between C and infinity, typically larger than object. Why others wrong: (a) virtual/erect occurs only when object is inside F; (c) diminished occurs when object is beyond C; (d) behind the mirror refers to virtual images.
Q49. Which surface separates two different media?
a) Interface
b) Axis
c) Aperture
d) Vertex
Answer: Interface.
Why correct: The interface is the boundary where properties (and therefore light speed) change causing refraction. Why others wrong: (b) axis is geometric line; (c) aperture is opening; (d) vertex/pole is part of mirror, not a medium boundary.
Q50. Lens formula is:
a) 1/f = 1/u + 1/v
b) f = uv
c) f = u – v
d) v = f + u
Answer: 1/f = 1/u + 1/v.
Why correct: The lens/mirror formula relates focal length f to object distance u and image distance v in thin-lens approximation. Why others wrong: (b)/(c)/(d) are incorrect algebraic relations not satisfying lens geometry.