What will be the nature of the image for an object placed at infinity a real and erect B Real and inverted C virtual and erect D virtual and inverted?

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.

(c) It bends away from the normal while travelling from a denser to a rarer 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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Since parallel rays coming from the object converge at principal focus, F of a concave mirror; after reflection. Hence, when the object is at infinity the image will form at F.

Fig: Object at Infinity

Properties of image:

• Point sized
• Highly diminished
• Real and inverted

Object between infinity and Centre of Curvature:

When object is placed between infinity and centre of curvature of a concave mirror the image is formed between centre of curvature (C) and focus (F).

Fig: Object Between Infinity and C

Properties of image:

• Diminished compared to object
• Real and inverted

When the object is placed at centre of curvature (C) of a concave mirror, a real and inverted image is formed at the same position.

Fig: Object at C

Properties of image:

• Same size as object
• Real and inverted

Object between Centre of curvature (C) and Principal Focus (F):

When the object is placed between centre of curvature and principal focus of concave mirror, a real image is formed beyond the centre of curvature (C).

Fig: Object between C and F

Properties of image:

• Larger than object
• Real and inverted

When the object is placed at principal focus (F) of a concave mirror, a highly enlarged image is formed at infinity.

Fig: Object at F

Properties of image:

• Highly enlarged
• Real and inverted

Object between Principal Focus (F) and Pole (P):

When the object is placed between principal focus and pole of a concave mirror, an enlarged, virtual and erect image is formed behind the mirror.

Fig: Object between F and P

Properties of image:

• Enlarged
• Virtual and erect

Positions of Object and Image in Concave Mirror
Position of Object	Position of Image	Size of Image	Nature of Image
At infinity	At focus	Point sized, highly diminished	Real and inverted
Between infinity and C	Between F and C	Dminished	Real and inverted
At C	At C	Same size	Real and inverted
Between C and F	Beyond C	Enlarged	Real and inverted
At F	At infinity	Highly enlarged	Real and inverted
Between F and P	Behind mirror	Enlarged	Virtual and erect

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