Question

The focal length of a lens depends on :

• A. color of light
• B. radius of curvature of the lens
• C. material of the lens
• D. all of the above

Answer 1

The correct option is D all of the above

Focal length depends on colour 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 curvature of lens,
i.e. $\frac{1}{f}=(\frac{M_2}{M_1}-1)(\frac{1}{R_1}-\frac{1}{R_2})$

where $R_1,R_2$ are radius of curvature of two sides of lens. And $M_2$ is refractive index of material of which lens is made of and $M_1$is refractive index of surrounding medium. And by this formula we see that focal length is also dependent on the material of lens.