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Q1. Convex mirrors are preferred as rear-view mirrors because:
Convex mirrors provide a wider field of view because they bulge outward. This allows the driver to see a larger area behind the vehicle, making driving safer. They form diminished images, not enlarged or inverted ones.
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Q2. Path of a ray of light passing through the focus of a concave mirror after reflection:
A ray passing through the focus of a concave mirror, after reflection, emerges parallel to the principal axis. This is the reverse of the rule that a ray parallel to the principal axis passes through the focus after reflection.
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Q3. Compared to plane mirror, a convex mirror gives:
Convex mirrors have a wider field of view than plane mirrors because they curve outward and reflect light from a larger area. This is why they are preferred in vehicles and for security purposes.
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Q4. Bending of light when it passes from one medium to another is called:
Refraction is the bending of light when it passes obliquely from one transparent medium to another. This happens because the speed of light changes in different media. Reflection is bouncing back, while dispersion is splitting of light into colors.
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Q5. A light ray passing through optical center of lens:
A ray passing through the optical center of a lens emerges without any deviation (it goes straight). This is because the two surfaces at the optical center are parallel, so the ray passes through without bending.
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Q6. In sign convention, focal length of a concave mirror is taken:
According to the Cartesian sign convention, the focal length of a concave mirror is taken as negative because the focus lies in front of the mirror (on the same side as the incident light). For a convex mirror, the focal length is positive.
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Q7. Principal focus of a concave mirror is the point where:
The principal focus (F) of a concave mirror is the point on the principal axis where parallel rays of light converge after reflection from the mirror. This is why concave mirrors are called converging mirrors.
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Q8. If magnification (m) = –1, the image is:
A magnification of –1 means the image is real (negative sign), inverted, and of the same size as the object. This happens when the object is placed at the centre of curvature (C) of a concave mirror.
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Q9. A real image can be obtained on:
A real image is formed when light rays actually meet at a point. Such an image can be obtained on a screen. Virtual images cannot be obtained on a screen because the rays only appear to meet behind the mirror.
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Q10. Mirror that always produces virtual and erect images:
A convex mirror always produces virtual and erect images regardless of the object’s position. Plane mirrors also produce virtual and erect images, but convex mirrors always form diminished images as well.
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Q11. Power of a lens is measured in:
The power of a lens is measured in dioptres (D). One dioptre is the power of a lens with a focal length of 1 meter. The formula is P = 1/f, where f is in meters. Watt is a unit of power (energy), not lens power.
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Q12. Image formed by a convex mirror is always:
A convex mirror always forms a virtual, erect, and diminished (smaller) image regardless of the object’s position. This property makes it useful for rear-view mirrors and security mirrors.
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Q13. A lens that is thick at the center and thin at edges is called:
A convex lens is thicker in the middle and thinner at the edges. It converges parallel rays of light to a point (focus). A concave lens is thinner in the middle and thicker at the edges.
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Q14. Refractive index is defined as ratio of:
Refractive index (n) is the ratio of the speed of light in a vacuum (or air) to the speed of light in a given medium. So, n = c/v. It tells us how much light slows down in a medium.
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Q15. Mirror used as a shaving mirror to see enlarged images:
A concave mirror is used as a shaving mirror because when the face is placed between the focus and the pole, it forms a virtual, erect, and enlarged image. This helps in seeing fine details clearly.
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Q16. Lens used in a magnifying glass:
A convex lens is used as a magnifying glass. When an object is placed between the lens and its focus, it forms a virtual, erect, and magnified image. Concave lenses cannot magnify objects.
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Q17. Focal length of convex mirror is always:
According to the sign convention, the focal length of a convex mirror is taken as positive because the focus lies behind the mirror (virtual focus). For a concave mirror, the focal length is negative.
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Q18. The phenomenon of a stick appearing bent in water is due to:
A stick appears bent when partly immersed in water because light from the submerged part bends as it travels from water to air. This refraction makes the stick look bent or broken at the water surface.
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Q19. Which lens is used to correct short-sightedness (myopia)?
Myopia (short-sightedness) is corrected using concave lenses. These lenses diverge light rays before they enter the eye, moving the focus back onto the retina so distant objects appear clear.
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Q20. The center of a spherical mirror is known as:
The pole (P) is the center of the reflecting surface of a spherical mirror. The centre of curvature (C) is the center of the hollow sphere from which the mirror is made, and the focus (F) is the point where parallel rays meet.
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Q21. Mirror used in street lamps for better illumination:
Concave mirrors are used in street lamps to direct light downwards over a large area. The light source is placed at the focus, and the reflected rays emerge as a parallel or concentrated beam.
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Q22. Laws of refraction are also known as:
The laws of refraction are called Snell’s laws, named after the Dutch mathematician Willebrord Snellius. They describe the relationship between the angles of incidence and refraction when light passes between two media.
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Q23. When light enters a denser medium from rarer medium, its speed:
When light enters a denser medium (like air to glass), its speed decreases because the denser medium has a higher refractive index. This slowing down causes the light to bend towards the normal.
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Q24. A concave mirror forms an erect and enlarged image when the object is placed:
A concave mirror forms an erect and enlarged image only when the object is placed between the focus (F) and the pole (P). This is the principle used in shaving mirrors and makeup mirrors.
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Q25. If radius of curvature is 30 cm, focal length is:
The focal length (f) is half of the radius of curvature (R). So, f = R/2 = 30/2 = 15 cm. This relationship (f = R/2) is true for all spherical mirrors.
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Q26. In ray diagrams, direction of incident light is taken:
In ray diagrams, the incident light is always taken as traveling from left to right (towards the mirror). According to the sign convention, distances measured in the direction of incident light are positive.
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Q27. A ray parallel to principal axis after reflection passes through:
A ray of light incident parallel to the principal axis of a concave mirror, after reflection, passes through the focus (F). This is one of the standard rules used in ray diagrams for concave mirrors.
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Q28. Uses of concave mirrors include which of the following?
Concave mirrors are used in solar furnaces to concentrate sunlight at the focus, producing intense heat. They are not used for wall decoration, in spectacles (lenses are used), or as security mirrors (convex mirrors are used).
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Q29. Distance between pole and focus is called:
Focal length (f) is the distance between the pole (P) and the focus (F) of a spherical mirror. The radius of curvature is the distance between the pole and the centre of curvature.
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Q30. Concave mirror forms image at focus when object is placed:
When the object is at infinity, the rays are parallel. After reflection from a concave mirror, they converge at the focus (F). This principle is used in solar cookers and telescopes.
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Q31. Which lens is used to correct long-sightedness (hypermetropia)?
Hypermetropia (long-sightedness) is corrected using convex lenses. These lenses converge light rays before they enter the eye, helping to focus nearby objects clearly on the retina.
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Q32. Eye defect that occurs due to weakening of ciliary muscles:
Presbyopia occurs with age when the ciliary muscles weaken and the eye lens loses its flexibility. This makes it difficult to see nearby objects clearly. It is corrected using bifocal lenses.
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Q33. The area of the spherical mirror used to reflect light is called:
The aperture of a spherical mirror is the area of the mirror surface that is actually used to reflect light. It determines how much light the mirror can gather. The pole is the center point of the reflecting surface.
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Q34. Convex mirrors are commonly used as:
Convex mirrors are commonly used as rear-view mirrors in vehicles because they provide a wider field of view. They are not used as magnifying glasses (convex lenses are used), shaving mirrors (concave mirrors are used), or projectors.
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Q35. A convex mirror always forms:
A convex mirror always forms a virtual and erect image. The image is also diminished (smaller). It is formed behind the mirror and cannot be obtained on a screen.
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Q36. Lens formula is:
The lens formula is 1/f = 1/v – 1/u or 1/v – 1/u = 1/f. The correct form is 1/f = 1/v – 1/u. This formula relates focal length (f), image distance (v), and object distance (u) for lenses.
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Q37. If image formed by a concave mirror is inverted and smaller than object, the object is placed:
When the object is placed beyond the centre of curvature (C), the image formed is real, inverted, and diminished (smaller than the object). This is used in cameras to capture distant objects.
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Q38. Focal length of a plane mirror is:
A plane mirror can be considered as a spherical mirror with an infinite radius of curvature. Since f = R/2, if R is infinity, f is also infinity. Plane mirrors do not converge or diverge light.
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Q39. Which surface separates two different media?
The interface is the boundary surface that separates two different media (like air and water, or air and glass). Refraction occurs at this interface when light passes from one medium to another.
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Q40. Dentists use concave mirrors to:
Dentists use concave mirrors to see enlarged images of teeth. When the tooth is placed between the focus and the pole, the mirror forms a virtual, erect, and magnified image, helping dentists see small cavities clearly.
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Q41. The image formed by a plane mirror is:
A plane mirror always forms a virtual, erect, and same-sized image. The image is formed behind the mirror and shows lateral inversion (left-right reversal). It cannot be obtained on a screen.
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Q42. Which of the following has the least refractive index?
Air has the lowest refractive index (approximately 1.0003) among the given options. Water has n ≈ 1.33, glass has n ≈ 1.50, and diamond has the highest n ≈ 2.42.
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Q43. Convex mirror is used as rear-view mirror because:
Convex mirrors are used as rear-view mirrors because they provide a wider field of view. Although they form diminished images, they allow the driver to see a larger area behind the vehicle.
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Q44. When object is placed between focus and centre of curvature of concave mirror, image is:
When the object is placed between the focus (F) and the centre of curvature (C), the image is formed beyond C. The image is real, inverted, and enlarged. This is used in projectors.
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Q45. Radius of curvature (R) and focal length (F) are related as:
The radius of curvature (R) is twice the focal length (F). So, R = 2F or F = R/2. This relationship holds true for all spherical mirrors.
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Q46. If magnification (m) > 1, then the image is:
Magnification (m) is the ratio of the height of the image to the height of the object. If m > 1, the image is larger than the object (enlarged). If m < 1, the image is diminished.
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Q47. Concave mirrors are used in torches and headlights to get:
Concave mirrors are used in torches and headlights to produce powerful parallel beams of light. The bulb is placed at the focus, and the reflected rays emerge parallel, illuminating a large area.
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Q48. Large concave mirrors are mostly used in:
Large concave mirrors are used in solar furnaces to concentrate sunlight at the focus, producing intense heat. Car side mirrors use convex mirrors, dressing tables use concave mirrors, and periscopes use plane mirrors.
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Q49. If radius of curvature of a concave mirror is 20 cm, focal length is:
The focal length (f) is half of the radius of curvature (R). So, f = R/2 = 20/2 = 10 cm. This is a fundamental relationship for spherical mirrors.
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Q50. A concave lens always forms image that is:
A concave lens always forms a virtual, erect, and diminished image regardless of the object’s position. The image is formed on the same side as the object and cannot be obtained on a screen