An object is placed at the centre of curvature of a concave mirror

Living Science Physics 8>Light Energy>Think and answer>Q 2

1. Refraction of light:

(i) Anything through which light can travel is called a medium. Vacuum, glass, air and water are all mediums through which light can travel.

(ii) The bending of light as it passes from one medium to another is called refraction. The amount of refraction (bending) that occurs depends on the nature of the two mediums.

(iii) The refractive index of one medium with respect to another is speed of light in the medium from which light is travellingspeed of light in the medium into which light is travelling .

(iv) When light travels from one medium to another:

(a) It bends only if it is incident at an angle to the normal.

(b) It bends towards the normal while travelling from a rarer to a denser medium.

(d) It retraces its path while moving in the reverse direction.

(v) When light travels through a rectangular glass slab, the emergent ray is parallel to the incident ray and is laterally shifted from it.

2. Prism:

(i) A prism is a piece of glass that has a triangular cross-section formed by three rectangular faces. The angle between two rectangular faces is called the angle of the prism, A.

(ii) When a ray of light passes through a prism, it bends towards the base of the prism. The angle between the incident ray and the emergent ray is the angle of deviation, d. For refraction through a prism, ∠i+∠e=∠A+∠d.

(iii) Atmospheric refraction is the bending of light as it passes through the atmosphere because of the variations in the density of air. Early sunrise, delayed sunset and the twinkling of stars are some effects of atmospheric refraction.

(iv) The separation of white light into its constituent colours is called dispersion. The band of colours (VIBGYOR) that light separates into is called its spectrum. Dispersion occurs because the refractive index of a medium is slightly different for lights of different colours.

3. Spherical mirror:

(i) In a convex mirror, the reflecting surface bulges outwards. In a concave mirror, the hollow part is made reflecting.

(ii) The centre of the imaginary sphere of which a spherical mirror is a part is called the centre of curvature (C). The radius of the sphere is called the radius of curvature (R). The centre of the mirror is called its pole (P). A diameter of the imaginary sphere passing through the pole is the principal axis of the mirror. The point lying midway between P and C is the focus (F). The distance PF= focal lengthf=R2.

(iii) When two rays start from a point O, move along different paths, and meet (intersect) again at some point I, an image of O is formed at I.

(iv) The nature of the image formed by a concave mirror depends on the distance of the object from the mirror.

(v) The image formed by a convex mirror is always virtual, erect and smaller than the object.

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Option 1 : Real and magnified

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10 Questions 10 Marks 10 Mins

CONCEPT:

The mirror which has a spherical reflection surface is called as spherical mirror.
The spherical mirror whose reflecting surface is away from the center of curvature is called as convex mirror.
Convex mirror always from a virtual image of any object.
The mirror whose reflecting surface is inward is called as concave mirror.
The concave mirror can form both real as well as virtual image of any object.

EXPLANATION:

Given: Focal length (f) of concave mirror = 16 cm

Since the object is shifted towards focus by 8 cm so object is between focus and center of curvature of the mirror.
When the object is between focus and Centre of curvature the image formed by the concave mirror is real and magnified. Hence option 1 is correct.