Question

A student wishes to study the cell structure under a light microscope having 10 X eyepiece and 45 X objective. He should illuminate the object, by which one of the following colours of light, the best possible resolution can be achieved?

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

Answer 1

The correct option is C Blue

Resolving power is the ability to distinguish two close objects as distinct. It is calculated by the formula 0.61 $\lambda$/ numerical aperture, where $\lambda$ is the wavelength of light and numerical aperture is the light collecting ability of lens. Actually, after calculations, the value comes out to be 0.5 $\lambda$ or one half the wavelength of illuminating light. The average wavelength of light used in microscopes is 500-600 nm. It gives a maximum resolution of 250-300 nm or 0.25 micrometer to 0.3 micrometer for optical microscope. Use of blue light or blue filters helps in achieving a resolution limit of 200 nm or 0.2 micrometer. This is because blue light has shorter wavelength as compared to red, yellow and green light.