Question

The focal length of a convex lens depends upon

• A. Frequency of the light ray
• B. Wavelength of the light ray
• C. Both $\left(a\right)$ and $\left(b\right)$
• D. None of these

Answer 1

The correct option is B Wavelength of the light ray

The focal length depends on the color of light because changing color changes wavelength which in turn changes the convergence point, so focus position changes and hence focal length also changes. It also depends on the curvature of the lens,

$f\propto \frac{1}{\mu -1}$ and $\mu \propto \frac{1}{\lambda }$