Question

A student wishes to study the cell structure under a light microscope having a 10X eyepiece and 45X objective. For best resolution the object should be illuminated by which light?
A) Blue
B) Green
C) Yellow
D) Red

Answer 1

A light or optical microscope uses visible light to focus a beam on a specimen. This goes through two different lenses to get the best possible resolution or separation of all the different elements of the object under observation.

Complete answer:
Blue light gives the best resolution under the light microscope. To know the smallest point that can be identified in an object, it is essential to know the wavelength of light involved. A shorter wavelength gives better resolving power. Answer A is the correct answer.

As wavelengths progress from near Ultraviolet light to the red spectrum, the resolving power of the microscope decreases. This is why green is not as efficient as blue light. Option B is incorrect.

Yellow light is closer to the long wavelength of red and is therefore not used in light microscopy if possible. With yellow light the refractive index decreases, and resolution is very poor. Option C is not correct.

Using red light to observe the specimen in a light microscope can actually reduce the resolving power by half. Option D is not correct.

Hence the correct answer is option ‘A’.

Note: In light microscopy there are different types of microscopes which may vary the number of lenses or the kind of light used, or the principle of contrast. These include phase contrast, bright field, fluorescence, and dark field light microscopes. All of these use a visible light source and cause the light to refract or bend with the help of a prism as it passes through the object under observation.