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📘 Study MCQs
Q1. In the sign convention for spherical mirrors, distances are measured from the __________.
• Centre of curvature
• Focus
• Pole
• Object
Answer: Pole
All distances are measured from the pole (P) of the mirror. The pole is the reference point for the sign convention.
Q2. According to the sign convention, distances measured in the direction of the incident light are taken as __________.
• Positive
• Negative
• Zero
• Infinite
Answer: Positive
Distances measured in the same direction as the incident light is traveling (usually from the mirror towards the object) are considered positive.
Q3. For a spherical mirror, the focal length (f) and object distance (u) are both negative. What type of mirror is it?
• Convex mirror
• Concave mirror
• Plane mirror
• Cannot determine
Answer: Concave mirror
For a concave mirror, the object distance (u) and focal length (f) are both negative as per the New Cartesian Sign Convention.
Q4. The mirror formula is __________.
• 1/v + 1/u = 1/f
• 1/v – 1/u = 1/f
• uv = f
• u + v = f
Answer: 1/v + 1/u = 1/f
The mirror formula relates the object distance (u), image distance (v), and focal length (f) as 1/v + 1/u = 1/f.
Q5. Magnification (m) for a mirror is the ratio of the height of the image to the __________.
• Height of the object
• Focal length
• Object distance
• Radius of curvature
Answer: Height of the object
Magnification, m = h_i / h_o, where h_i is image height and h_o is object height.
Q6. Magnification can also be calculated using the formula m = __________.
• -v/u
• v/u
• u/v
• -f/u
Answer: -v/u
For spherical mirrors, magnification is given by the negative of the ratio of image distance (v) to object distance (u), i.e., m = -v/u.
Q7. A positive magnification value indicates that the image is __________.
• Real
• Inverted
• Virtual and erect
• Diminished
Answer: Virtual and erect
A positive sign for magnification means the image is erect. Since real images are inverted, a positive magnification indicates a virtual and erect image.
Q8. The bending of light as it passes from one medium to another is called __________.
• Reflection
• Dispersion
• Refraction
• Scattering
Answer: Refraction
Refraction is the phenomenon where light changes direction (bends) when it travels from one transparent medium to another with a different density.
Q9. The Refractive Index is the ratio of the speed of light in vacuum to the speed of light in __________.
• Air
• Water
• The medium
• Glass
Answer: The medium
The refractive index (n) of a medium = (Speed of light in vacuum) / (Speed of light in the medium).
Q10. Which medium has the highest refractive index among the given options?
• Water
• Crown glass
• Diamond
• Alcohol
Answer: Diamond
Diamond has a very high refractive index of 2.42, which is why it sparkles so much. The other options have lower indices.
Q11. Which medium has the lowest refractive index among the given common materials?
• Air
• Water
• Kerosene
• Ice
Answer: Air
Air has a refractive index very close to 1 (1.0003). Other materials like water (1.33), ice (1.31), and kerosene (1.44) have higher indices.
Q12. A transparent material with a curved surface, used to converge or diverge light, is called a __________.
• Mirror
• Prism
• Lens
• Glass slab
Answer: Lens
A lens is a piece of transparent material, like glass, bounded by one or two spherical surfaces, used to refract light.
Q13. A lens that is thicker in the middle and thinner at the edges is a __________ lens.
• Concave
• Convex
• Plano-concave
• Biconcave
Answer: Convex
A convex lens converges light and is thicker at the center than at the edges. It is also called a converging lens.
Q14. For a convex lens, a real and inverted image is formed when the object is placed __________.
• Between the lens and its focus
• At the focus
• Beyond the focus
• Anywhere
Answer: Beyond the focus
A convex lens forms a real and inverted image when the object is placed anywhere beyond its focal point (F).
Q15. The formula that relates object distance (u), image distance (v), and focal length (f) for a lens is __________.
• 1/v – 1/u = 1/f
• 1/v + 1/u = 1/f
• 1/u – 1/v = 1/f
• uv = f
Answer: 1/v – 1/u = 1/f
The lens formula is 1/v – 1/u = 1/f. Note the sign difference from the mirror formula.
Q16. The power of a lens is defined as the reciprocal of its __________.
• Diameter
• Focal length
• Radius of curvature
• Thickness
Answer: Focal length
Power of a lens, P = 1/f, where f is the focal length measured in meters. Its unit is Dioptre (D).
Q17. The unit of power of a lens is __________.
• Meter
• Centimeter
• Dioptre
• Joule
Answer: Dioptre
The SI unit of lens power is the dioptre (D). 1 D = 1 m⁻¹.
Q18. A convex lens has a __________ focal length and __________ power.
• Positive, positive
• Negative, negative
• Positive, negative
• Negative, positive
Answer: Positive, positive
A convex lens is a converging lens. Its focal length is taken as positive, and therefore its power is also positive.
Q19. A concave lens always forms a __________ image.
• Real, inverted, and diminished
• Virtual, erect, and diminished
• Real, erect, and magnified
• Virtual, inverted, and magnified
Answer: Virtual, erect, and diminished
For all positions of a real object, a concave (diverging) lens always produces a virtual, erect, and diminished image.
Q20. Magnification for a lens is given by the formula m = __________.
• v/u
• u/v
• -v/u
• h_o / h_i
Answer: v/u
For lenses, magnification is given by the ratio of the image distance (v) to the object distance (u), i.e., m = v/u. There is no negative sign as in mirrors, though the nature of the image is determined by other rules.
Q21. If the magnification produced by a lens is +2, the image is __________.
• Real and inverted
• Virtual and inverted
• Virtual and erect
• Real and erect
Answer: Virtual and erect
For lenses, a positive magnification value indicates that the image is erect. Since real images from lenses are inverted, a positive magnification means the image is virtual and erect.
Q22. Which type of lens is used to correct myopia (short-sightedness)?
• Convex lens
• Concave lens
• Cylindrical lens
• Bifocal lens
Answer: Concave lens
A concave (diverging) lens is used to correct myopia as it helps diverge the light rays before they enter the eye, allowing the image to focus on the retina.
Q23. The refractive index of water is approximately __________.
• 1.00
• 1.33
• 1.50
• 2.42
Answer: 1.33
The refractive index of water is about 1.33. This means light travels about 1.33 times slower in water than in a vacuum.
Q24. Light travels fastest in which medium?
• Glass
• Water
• Vacuum
• Diamond
Answer: Vacuum
Light travels fastest in a vacuum (3 x 10⁸ m/s). It slows down when it enters any material medium.
Q25. According to the sign convention for lenses, the focal length of a convex lens is __________.
• Positive
• Negative
• Zero
• Infinite
Answer: Positive
Convex lenses are converging lenses. Their focal length is taken as positive.
Q26. A lens with a power of +4.0 D is a __________ lens.
• Concave
• Convex
• Plane
• Cannot say
Answer: Convex
A positive power indicates a converging lens, which is a convex lens.
Q27. If the image distance (v) is positive for a lens, the image is formed on the __________ side.
• Same as the object
• Opposite to the object
• On the lens itself
• Cannot say
Answer: Opposite to the object
For lenses, a positive image distance (v) means the image is formed on the side opposite to the object. This is typically a real image for a convex lens.
Q28. Which lens has a negative focal length?
• Convex lens
• Concave lens
• Both
• Neither
Answer: Concave lens
A concave (diverging) lens has a negative focal length as per the sign convention.
Q29. When an object is placed at 2F (twice the focal length) of a convex lens, the image is formed __________.
• At F
• At 2F on the other side
• At infinity
• Between F and 2F
Answer: At 2F on the other side
For a convex lens, when the object is at 2F, the image is also formed at 2F on the opposite side. It is real, inverted, and the same size as the object.
Q30. The refractive index of a medium depends on the __________ of light.
• Intensity
• Speed
• Color (wavelength)
• Source
Answer: Speed
The refractive index depends on how much the speed of light is reduced in that medium compared to a vacuum.
Q31. Which of the following has a refractive index greater than 1.5?
• Water
• Crown glass
• Dense flint glass
• Alcohol
Answer: Dense flint glass
Dense flint glass has a refractive index of 1.65, which is greater than 1.5. Water (1.33), Crown glass (1.52), and Alcohol (1.36) are lower.
Q32. Snell’s Law relates the angles of incidence and refraction with the __________.
• Focal length
• Refractive indices
• Object distance
• Image distance
Answer: Refractive indices
Snell’s Law states: n₁ sin i = n₂ sin r, where n₁ and n₂ are the refractive indices of the two media.
Q33. A lens forms an image that is four times the size of the object. The magnification is __________.
• 4
• 1/4
• -4
• -1/4
Answer: 4
Magnification is the ratio of image size to object size. If the image is four times larger, m = 4. The sign would depend on whether it’s erect or inverted.
Q34. The power of a lens with a focal length of 0.5 meters is __________.
• 0.5 D
• 1 D
• 2 D
• 4 D
Answer: 2 D
Power P = 1/f (in meters). So, P = 1 / 0.5 = 2 Dioptres.
Q35. A concave lens is also called a __________ lens.
• Converging
• Diverging
• Magnifying
• Focusing
Answer: Diverging
A concave lens causes parallel rays of light to spread out (diverge) after passing through it.
Q36. For a lens, if the object distance (u) is negative, it means the object is __________.
• Virtual
• On the same side as incident light
• Real and placed on the opposite side
• Always real
Answer: Real and placed on the opposite side
By sign convention for lenses, a negative object distance (u) indicates that the object is real and is placed on the side from which light is coming (the conventional object side).
Q37. Which of these materials is likely to bend light the most?
• Air (n=1.0003)
• Water (n=1.33)
• Glass (n~1.5)
• Diamond (n=2.42)
Answer: Diamond
The higher the refractive index, the greater the bending (refraction) of light. Diamond has the highest index.
Q38. The image formed by a convex lens is virtual and erect when the object is placed __________.
• At 2F
• Beyond 2F
• At F
• Between the lens and F
Answer: Between the lens and F
A convex lens produces a virtual, erect, and magnified image only when the object is placed between the principal focus (F) and the optical center of the lens.
Q39. Two lenses of power +2.0 D and -0.5 D are placed in contact. The combined power is __________.
• +1.5 D
• +2.5 D
• -1.5 D
• +0.5 D
Answer: +1.5 D
The powers of lenses in contact add up. Combined Power = P1 + P2 = (+2.0) + (-0.5) = +1.5 D.
Q40. The principal focus of a concave lens is __________.
• Real
• Virtual
• Positive
• On the same side as the object
Answer: Virtual
For a concave lens, the rays diverge and appear to come from a point on the same side as the object. This point is a virtual focus.
Q41. The lens formula, 1/v – 1/u = 1/f, is applicable to __________.
• Only convex lenses
• Only concave lenses
• Both convex and concave lenses
• Only spherical mirrors
Answer: Both convex and concave lenses
The lens formula is a universal formula relating u, v, and f, applicable to both types of spherical lenses when the sign convention is followed.
Q42. If the magnification is less than 1 (|m| < 1), the image is __________.
• Enlarged
• Same size
• Diminished
• Inverted
Answer: Diminished
If the magnitude of magnification is less than 1, it means the image is smaller than the object, i.e., diminished.
Q43. Which lens is used as a simple microscope (magnifying glass)?
• Concave lens
• Convex lens of short focal length
• Convex lens of long focal length
• Concave mirror
Answer: Convex lens of short focal length
A convex lens with a short focal length acts as a simple magnifying glass when the object is placed within its focal length, producing a magnified virtual image.
Q44. The speed of light in a medium with refractive index 1.5 is __________.
• 2 x 10⁸ m/s
• 3 x 10⁸ m/s
• 4.5 x 10⁸ m/s
• 1.5 x 10⁸ m/s
Answer: 2 x 10⁸ m/s
Speed in medium = (Speed in vacuum) / n = (3 x 10⁸ m/s) / 1.5 = 2 x 10⁸ m/s.
Q45. A real image formed by a lens can be obtained on a __________.
• Mirror
• Lens itself
• Screen
• It cannot be obtained
Answer: Screen
A real image is formed where light rays actually meet. It can be captured or projected onto a screen.
Q46. The refractive index of a medium is always __________.
• Less than 1
• Equal to 1
• Greater than 1
• Greater than or equal to 1
Answer: Greater than or equal to 1
The refractive index is the ratio of the speed in vacuum to speed in the medium. Since light travels fastest in vacuum, n is always ≥ 1.
Q47. When light enters a denser medium from a rarer medium, it bends __________ the normal.
• Away from
• Towards
• Parallel to
• Does not bend
Answer: Towards
When light goes from a rarer (like air) to a denser medium (like glass), it slows down and bends towards the normal line.
Q48. A lens of power -2.0 D is a __________ lens of focal length __________ m.
• Convex, +0.5
• Concave, -0.5
• Convex, -0.5
• Concave, +0.5
Answer: Concave, -0.5
Negative power indicates a concave (diverging) lens. f = 1/P = 1/(-2.0) = -0.5 m.
Q49. Which of these statements about magnification is true?
• It has a unit.
• It is always positive.
• It is the ratio of image distance to object distance for lenses.
• It is always greater than 1.
Answer: It is the ratio of image distance to object distance for lenses.
For lenses, magnification m = v/u (the height ratio is also valid). It is a ratio with no unit, can be positive or negative, and can be less than, equal to, or greater than 1.
Q50. For a convex lens, if the object is placed at the focus (F), the image is formed at __________.
• F
• 2F
• Infinity
• Between F and 2F
Answer: Infinity
When an object is placed at the principal focus of a convex lens, the refracted rays become parallel to the principal axis. Therefore, the image is formed at infinity.