A thin convex lens is made of two materials with refractive indices $$n_1 and n_2$$ as shown in figure. The radius of curvature of the left and right spherical surfaces are equal. f is the focal length of the lens when $$n_1 = n_2 = n.$$ The focal length is $$f + \triangle f$$ when $$n_1 = n$$ and $$n_2 = n + \triangle n$$. Assuming $$\triangle n \ll (n — 1)$$ and 1 < n < 2, the correct statement(s) is/are

$$| \frac {\triangle f}{f}| < | \frac {\triangle n}{n}|$$

For $$n = 1.5, \triangle n = 10^{-3}$$ and f = 20 cm,the value of $$|\triangle f|$$ will be 0.02 cm (round off to $$2^{nd}$$ decimalplace).

If $$\frac {\triangle n}{n} < 0 then \frac {\triangle f}{f} > 0$$

The relation between $$\frac {\triangle f}{f} and \frac {\triangle n}{n}$$ remains unchanged if both the convex surfaces are replaced by concave surfaces of the same radius of curvature.