Lakhmir Singh Physics Class 10 Solutions Page No:192
Question 1: According to the “New Cartesian Sign Convention” for mirrors, what sign has been given to the focal length of :
(i) a concave mirror ?
(ii) a convex mirror ?
Solution : (i) Negative
Question 2: Which type of mirror has :
(a) positive focal length ?
(b) negative focal length ?
Solution : (a) Convex mirror.
(b) Concave mirror.
Question 3: What is the nature of a mirror having a focal length of, +10 cm ?
Solution : Convex mirror (since focal length is positive).
Question 4: What kind of mirror can have a focal length of, – 20 cm ?
Solution : Concave mirror (since focal length is negative).
Question 5: Complete the following sentence :
All the distances are measured from the……….. of a spherical mirror.
Solution : Pole
Question 6: What sign (+ve or -ve) has been given to the following on the basis of Cartesian Sign Convention ?
(a) Height of a real image.
(b) Height of a virtual image.
Solution : (a) Negative.
Question 7: Describe the New Cartesian Sign Convention used in optics. Draw a labelled diagram to illustrate this sign convention.
Solution : According to the New Cartesian Sign Convention:
(i) All the distances are measured from pole of the mirror as origin.
(ii) Distances measured in the same direction as that of incident light are taken as positive.
(iii) Distances measured against the direction of incident light are taken as negative.
(iv) Distances measured upward and perpendicular to the principal axis are taken as positive.
(v) Distance measured downward and perpendicular to the principal axis are taken as negative.