MHTCET 16 Apr 2026 Shift 1 Paper

Concept:The magnifying power of a simple microscope depends on the focal length of its lens, which changes with the colour of light.Explanation:For a simple microscope, the magnifying power is given by $M = \frac{D}{f}$ in normal adjustment.When the final image is formed at the least distance of distinct vision, $M = 1 + \frac{D}{f}$.In both cases, $M$ is inversely proportional to the focal length $f$.The focal length of a lens depends on the refractive index $\mu$ of the glass.Using the lens maker's formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$.Blue light has a shorter wavelength, so the refractive index of glass is higher for blue light than for red light.Therefore, for blue light, $\mu$ is larger, which gives a smaller focal length $f$.For red light, $\mu$ is smaller, so the focal length $f$ becomes larger.Since magnifying power is inversely proportional to $f$, changing from blue light to red light increases $f$ and thus decreases the magnifying power.Answer:Option A: decreases