Ray Optics and Optical Instruments - Result Question 43
45. The focal length of converging lens is measured for violet, green and red colours. It is respectively $f_v, f_g, f_r$. We will get
(a) $f_y=f_g$
(c) $f_v<f_r$
(b) $f_g>f_r$
[1997]
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Answer:
Correct Answer: 45. (c)
Solution:
- (c) Red light has wavelength greater than violet light. Therefore focal length of lens for red is greater than for violet. $(f_r>f_v)$
Cauchy relation
$\mu=A+\frac{B}{\lambda^{2}}+\frac{C}{\lambda^{4}} \cdots \quad$ Hence $f \propto \lambda$.
