1. Reflection of light:

(i) Light travels in straight lines and does not bend around the corners. This is known as rectilinear propagation of light.

(ii) Reflection is the phenomenon due to which a ray of light bounces off a smooth polished surface in the same medium.

(iii) Image is a view of a well-illuminated object in a mirror or through a lens.

(iv) The real image is an image formed by the actual convergence of rays of light which are reflected by a mirror or pass through a lens. It can be obtained on the screen.

(v) A virtual image is an image in which the rays reflected by a mirror or on passing through a lens, diverge, but to the eye, they appear to converge at some point. It cannot be obtained on the screen.

2. Mirror:

(i) A mirror is a smooth polished surface from which reflection takes place.

(ii) A plane mirror always forms a virtual image, which is as far behind the mirror, as the object is in front of it. Image is erect and is of the same size as the object.

(iii) The concave mirror is a reflecting surface which curves inward.

(iv) The convex mirror is a reflecting surface which curves outward.

(v) A concave mirror always forms a real and inverted image, which may be magnified or diminished, except when the object is held close to the mirror. In such a case, it always forms a virtual, erect and magnified image.

(vi) A convex mirror always forms a virtual, erect and diminished image.

3. Lens:

(i) The lens is a piece of transparent material which has one or two spherical surfaces.

(ii) The concave lens is a lens which is thicker at the edges and tapering in the middle.

(iii) The convex lens is a lens which is thicker in the middle and tapering at the edges.

(iv) A convex lens always forms a real and inverted image which may be magnified or diminished, except when the object is held close to the lens. In such a case, it always forms a virtual, erect, and magnified image.

(v) A concave lens always forms a virtual, erect, and diminished image.

4. Dispersion:

(i) Dispersion is the phenomenon due to which white light splits into seven colours (VIBGYOR).

(ii) Rainbow is an arc consisting of seven colours (VIBGYOR) formed in the sky, just after the rain during the daytime.

(iii) The seven colours of white light (VIBGYOR) can be combined by rapidly rotating Newton's colour disc.

A partial lunar eclipse occurs when the umbra obscures the whole of the moon's visible surface.

Important Questions on Light

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