Physics
What are the three principal rays that are drawn to construct the ray diagram for the image formed by a lens? Draw diagrams to support your answer.
Answer
(i) A ray of light incident at the optical centre O of the lens passes undeviated through the lens.
Convex Lens
Concave Lens
(ii) A ray of light incident parallel to the principal axis of the lens, after refraction passes through the second focus F2 (in a convex lens) or appears to come from the second focus F2 (in a concave lens), respectively.
Convex Lens
Concave Lens
(iii) A ray of light passing through the first focus F1 (in a convex lens) or directed towards the first focus F1 (in a concave lens), emerges parallel to the principal axis after refraction, respectively.
Convex Lens
Concave Lens
Related Questions
State whether the following statements are 'true' or 'false' by writing T/F against them.
(a) A convex lens has a divergent action and a concave lens has a convergent action.
(b) A concave lens, if kept at a proper distance from an object, can form its real image.
(c) A ray of light incident parallel to the principal axis of a lens, passes undeviated after refraction.
(d) A ray of light incident at the optical centre of a lens, passes undeviated after refraction.
(e) A concave lens forms a magnified or diminished image depending on the distance of an object from it.
Where must a point source of light be placed in front of a convex lens so as to obtain a parallel beam of light?
In the diagrams below, XX' represents the principal axis, O the optical centre and F the focus of the lens. Complete the path of the rays A and B as they emerge out of the lens.
(a)
(b)
Distinguish between a real and a virtual image.