Question

The limitation in using an optical microscope for measuring small dimensions is-
1. extremely small objects cannot be focused by the microscope
2. it can only measure length along one direction
3. the wave nature of light cannot help resolve smaller particles
4. none of the above

Answer 1

Correct Answer - Option 3 : the wave nature of light cannot help resolve smaller particles

The correct answer is option 3) i.e. the wave nature of light ​cannot help resolve smaller particles

CONCEPT:

• Estimation of very small distances:
  • ​Measurements of the order of 10^-8 m or 10^-12 m cannot be measured directly using a geometric ruler or vernier calipers.
  • Such dimensions can only be measured if they can be viewed under microscopes of high magnification or by using some indirect methods.
  • An optical microscope is an instrument that can help in measuring smaller dimensions.

EXPLANATION:

• An optical microscope is also known as a light microscope.
• It creates a magnified image of an object using an objective lens and magnifies this image further with an eyepiece. This allows the user to observe it by the naked eye. 
• Since it uses visible light to view the object, the resolution to which an optical microscope can be used depends on the wavelength of light.
• For visible light, the range of wavelengths is 4000 Å to 7000 Å (where 1 Å = 10^-10 m).
• Hence, an optical microscope cannot resolve particles that are smaller than the wavelength size of visible light. 
• Thus, the limitation in using an optical microscope for measuring small dimensions is the wave nature of light.