Resolving Power of Optical Instruments

Chapter-10|Wave Optics|NCERT 12th Physics:

Resolving Power of Optical Instruments:

Resolving power of an optical instrument is the ability of the instrument to produce separate image of two close objects.

According to Rayleigh, two point objects A and B will be just resolved, when Central maximum of diffraction pattern of B lies on first secondary minimum of diffraction pattern of A.

# The minimum distance between two objects, which can just be seen as separate by the optical instrument is called the limit of the resolution of the instrument.

Resolving Power of a Microscope:

The resolving power of a microscope is defined as the reciprocal of the distance between two objects which can be just resolved when seen through the microscope.

Resolving power of microscope depends on-

(I) Refractive index of the medium between the object and the objective lens of microscope.

(II) Wavelength λ of light.

(III) Half angle θ or β of the cone of light from one of the objects.

Note: If we put microscope in oil then its resolving power will be increased because μ will be increased. Refractive index of oil is greater than refractive index of air.

Resolving Power of a Telescope:

The resolving power of a telescope is define as the reciprocal of the smallest angular separation between two distant objects, whose images are to be seen separately.

Resolving power of telescope depends on-

(I) Wavelength λ of light.

(II) Diameter of objective.