What is a compound microscope? Describe its construction and working. What is its magnifying power?

A compound microscope is an optical instrument that uses more than one lens to magnify small objects. It is commonly used in laboratories for examining specimens like cells, bacteria, or thin slices of biological tissues.

Construction of a Compound Microscope:

The basic construction of a compound microscope involves several key parts:

  1. Eyepiece (ocular lens): This is the lens closest to the eye, through which the observer views the specimen. It typically has a magnifying power of 10x.

  2. Objective lenses: These are the lenses that are closest to the specimen. A compound microscope usually has multiple objective lenses of different magnifications, such as 4x, 10x, 40x, or 100x. These are mounted on a rotating nosepiece, allowing the user to switch between different lenses for varied magnification.

  3. Stage: The platform where the specimen is placed for viewing. It usually has clips to hold the specimen in place and may have mechanical adjustments to move the slide around.

  4. Condenser: The condenser focuses light onto the specimen. In some microscopes, it is adjustable to control the intensity and size of the light beam.

  5. Diaphragm or iris: This part controls the amount of light that passes through the specimen. Adjusting it can improve contrast and resolution.

  6. Light source: A light bulb or mirror that provides light for illuminating the specimen. In modern microscopes, this is typically an LED light source placed beneath the stage.

  7. Arm and base: The arm holds the eyepiece and objective lenses in place, while the base provides support and houses the light source.

  8. Coarse and fine focus knobs: These are used to adjust the focus of the image. The coarse focus knob makes large adjustments, while the fine focus knob is used for fine-tuning the image clarity.

Working of a Compound Microscope:

The working principle of a compound microscope involves the use of multiple lenses to magnify an object.

  1. Illumination: The light from the source (either a mirror or an electric bulb) passes through the condenser and the diaphragm, which control the size and intensity of the light that reaches the specimen.

  2. Objective lenses: The light that passes through the specimen is captured by the objective lens. The objective lens produces a real, inverted image of the specimen at a high magnification.

  3. Eyepiece: The eyepiece further magnifies the image formed by the objective lens. It works as a simple magnifying lens, allowing the observer to see the specimen in more detail.

In essence, the compound microscope combines the magnification of the objective lens and the eyepiece to provide an overall higher magnification and clearer view of small objects.

Magnifying Power:

The magnifying power of a compound microscope is determined by the magnifying power of the eyepiece and the objective lens.

  • Total Magnification = Magnification of the eyepiece × Magnification of the objective lens.

For example, if the eyepiece has a magnifying power of 10x, and the objective lens is 40x, the total magnification would be:

10x × 40x = 400x

Thus, the total magnification of a compound microscope can range from around 40x (with low-power objective) to 1000x (with high-power objectives). Some advanced microscopes may allow for even higher magnification, especially when using oil immersion techniques for the highest magnification objectives (typically 100x)

Related Questions:

  1. What is reflection of light? Define the following terms: Incident ray, reflected ray, normal, angle of incidence, and angle of reflection. Describe the laws of reflection.
  2. What are different spherical mirrors? Define different terms involved in spherical mirrors.
  3. Why is a concave mirror called a converging mirror? Why is a convex mirror called a diverging mirror?
  4. Define the principal focus of convex and concave mirrors. Define focal length. Which mirror has a positive focal length? Which has a negative focal length and why?
  5. What is the spherical mirror formula? Also, write down the sign conventions for the spherical mirror formula.
  6. Differentiate between real and virtual images. What are three basic rays by which we can draw a ray diagram to form an image by a spherical mirror?
  7. What is refraction of light? Show by ray diagram how light bends when it travels from rare to denser medium and from denser to rare medium. Define the refractive index of a medium. What are its different formulae?
  8. What are the laws of refraction? Explain with the help of ray diagrams
  9. Explain the phenomenon of total internal reflection. What are necessary conditions to perform total internal reflection? Derive the formula for the refractive index of a medium in terms of the critical angle.
  10. What is optical fibre? How does light travel through it? Explain.
  11. What is a lens? What are its types? Define the basic terminologies of lenses.
  12. Define and explain the terms: resolving power and magnifying power.
  13. What is a magnifying lens or simple microscope? How can a convex lens behave as a magnifying glass? What is its magnifying power? Why must a convex lens of short focal length be used as a magnifying glass?
  14. What is an astronomical telescope? Describe its construction and working. What is its magnifying power? Under what conditions does an astronomical telescope act in normal adjustment?
  15. What are defects of vision? What are the causes of each defect? How can we remove these defects of vision?
  16. When you look at the front side of a polished spoon, your image is inverted, and from the back of the spoon, your image is erect. Explain why?
  17. Which mirror is used by girls for makeup and why?
  18. Why are large convex mirrors fixed at blind turns of mountains?
  19. Which mirrors are used for the rear view of vehicles and why?
  20. If a person is walking in a pool, why do his legs appear shorter in water?