Question

Focal length of a convex lens will be maximum for

• A. Green Light
• B. Blue Light
• C. Red Light
• D. Yellow Light

Answer 1

The Correct Option is C

The focal length of a convex lens is influenced by the refractive index of the material it is composed of and the wavelength of light passing through it. The refractive index of a material varies slightly with different wavelengths of light, which in turn affects the focal length.

In general, the refractive index of a material decreases as the wavelength of light increases. This phenomenon is known as dispersion. Among the options given, red light has the longest wavelength (longer than green, blue, and yellow light), so the refractive index of the lens material will be the least for red light.

According to the lens maker's formula, a lower refractive index corresponds to a longer focal length for a convex lens. Therefore, the focal length of a convex lens will be maximum for (C) red light.

Answer 2

The focal length of a convex lens is influenced by the refractive index of the lens material, which can vary depending on the wavelength (or color) of light. This variation is referred to as chromatic aberration.

In general, the refractive index of a material is higher for shorter wavelengths, such as blue light, and lower for longer wavelengths, such as red light. Consequently, the focal length of a convex lens is shorter for shorter wavelengths and longer for longer wavelengths.

Given this information, the focal length of a convex lens will be maximum for red light. Red light has a longer wavelength compared to green, blue, and yellow light. Therefore, when red light is used, a convex lens will exhibit the maximum focal length.