krit.club logo

Microscope and Microscopy - Parts of a Compound microscope-advanced

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

A compound microscope is an optical instrument used to observe small objects by using two sets of lenses: the ocular lens (eyepiece) and the objective lens.

•

The magnification of a compound microscope is the product of the magnification of the objective lens and the magnification of the ocular lens. It is expressed as Mtotal=Mobjective×MeyepieceM_{total} = M_{objective} \times M_{eyepiece}.

•

Resolving Power (Resolution) is the ability of the microscope to distinguish two closely spaced points as separate entities. It is inversely proportional to the wavelength of light used: d=λ2⋅NAd = \frac{\lambda}{2 \cdot NA}.

•

Numerical Aperture (NANA) represents the light-gathering capacity of the objective lens. It is defined by the formula NA=nsin⁡θNA = n \sin \theta, where nn is the refractive index of the medium between the lens and the specimen.

•

The Condenser and Iris Diaphragm are critical for controlling illumination. The condenser focuses light onto the specimen, while the iris diaphragm controls the intensity and cone of light reaching the specimen to improve contrast.

•

Mechanical parts include the Base (support), Arm (carrying handle), Stage (platform for slides), and Adjustment Knobs (Coarse for general focus and Fine for sharp detail).

📐Formulae

Mtotal=Mocular×MobjectiveM_{total} = M_{ocular} \times M_{objective}

NA=nsin⁡θNA = n \sin \theta

Limit of Resolution (d)=λ2⋅NALimit\ of\ Resolution\ (d) = \frac{\lambda}{2 \cdot NA}

💡Examples

Problem 1:

Calculate the total magnification of a compound microscope if the ocular lens has a power of 10x10x and the high-power objective lens has a power of 45x45x.

Solution:

Mtotal=10×45=450xM_{total} = 10 \times 45 = 450x

Explanation:

To find the total magnification, we multiply the magnifying power of the eyepiece (ocular lens) by the magnifying power of the objective lens being used.

Problem 2:

If a microscope uses light with a wavelength λ=550 nm\lambda = 550\text{ nm} and the objective lens has a Numerical Aperture (NANA) of 1.11.1, calculate the limit of resolution (dd).

Solution:

d=λ2⋅NAd = \frac{\lambda}{2 \cdot NA} d=5502×1.1d = \frac{550}{2 \times 1.1} d=5502.2=250 nmd = \frac{550}{2.2} = 250\text{ nm}

Explanation:

The limit of resolution is the smallest distance between two points that can still be distinguished. Using Abbe's formula, we divide the wavelength by twice the numerical aperture.