Slide 1

• Topic: Microscopes and Telescopes - Ray Optics and Optical Instruments – An introduction
• 12th Boards Physics Lecture

Slide 2

• In the realm of Ray Optics, optical instruments such as microscopes and telescopes play a crucial role.
• These instruments utilize the principles of refraction and reflection to enhance our ability to observe objects.
• Let’s delve into the world of microscopes and telescopes and explore their working principles.

Microscopes

• A microscope is an optical instrument used to magnify tiny objects or details that are not visible to the naked eye.
• It employs the phenomenon of refraction to magnify the image of an object.
• Microscopes are widely used in various scientific fields, such as biology, medicine, and materials science.

Types of Microscopes

1. Compound Microscope:
   • Consists of two lenses: the objective lens and the eyepiece.
   • Provides higher magnification and resolution compared to other types.

2. Simple Microscope:
   • Consists of a single lens.
   • Used for lower magnification applications.

3. Electron Microscope:
   • Utilizes beams of electrons instead of light rays.
   • Provides much higher magnification and resolution than optical microscopes.

Working Principle of a Compound Microscope

1. The objective lens forms a real and magnified image of the object.

2. The eyepiece acts as a magnifying glass, creating a virtual image of the real image.

3. The combined effect of both lenses results in an enlarged and highly magnified image.

Telescopes

• Telescopes allow us to observe distant celestial objects such as stars, galaxies, and planets.
• They work on the principle of reflection or refraction of light, depending on the type of telescope.
• Telescopes have revolutionized our understanding of the universe.

Types of Telescopes

1. Refracting Telescopes:
   • Use lenses to gather and focus light.
   • Examples: Galileo’s telescope, Hubble Space Telescope.

2. Reflecting Telescopes:
   • Employ mirrors to gather and focus light.
   • Examples: Newtonian telescope, Cassegrain telescope, Schmidt-Cassegrain telescope.

Light Gathering Power

• The light gathering power of a telescope is directly related to the diameter of its objective lens or mirror.
• A larger objective collects more light, allowing for better observation of faint objects and increased image brightness.

Angular Magnification

• The angular magnification of a telescope is determined by the ratio of the focal lengths of the objective and eyepiece lenses.
• It defines how much larger an object appears when viewed through the telescope compared to the naked eye.

Resolution

• Resolution determines the level of detail discernible in an image.
• It is inversely proportional to the size of the Airy disc, which depends on factors like aperture size and wavelength.
• Telescopes with larger apertures can achieve higher resolution and observe smaller details.

Components of a Compound Microscope

• Eyepiece: Magnifies the image formed by the objective lens.
• Objective Lens: Forms the real magnified image of the object.
• Coarse Adjustment Knob: Moves the stage up and down for focusing.
• Fine Adjustment Knob: Provides fine-tuning for precise focusing.
• Stage: Platform to hold the specimen.
• Diaphragm: Controls the amount of light passing through the specimen.
• Light Source: Provides illumination for the specimen.

Magnification Formula for a Compound Microscope

• The total magnification of a compound microscope is given by:
  • Total Magnification = Magnification of Objective Lens × Magnification of Eyepiece

Working Principle of a Refracting Telescope

1. Objective Lens:
   • Collects and focuses light rays from the observed object.

2. Eyepiece Lens:
   • Magnifies the image formed by the objective lens.

3. Focal Lengths:
   • The objective lens has a longer focal length, while the eyepiece lens has a shorter focal length.

Resolution Formula for a Telescope

• The angular resolution, or smallest resolvable angle, of a telescope is given by:
  • Angular Resolution = 1.22 × (Wavelength of Light)/(Diameter of Telescope)

Types of Telescopes: Advantages and Disadvantages

1. Refracting Telescopes:
   • Advantages: Provide high contrast and sharp images.
   • Disadvantages: Prone to chromatic aberration, heavier and more expensive for larger apertures.

2. Reflecting Telescopes:
   • Advantages: No chromatic aberration, more compact and cost-effective for larger apertures.
   • Disadvantages: Require periodic mirror alignment.

Applications of Microscopes

1. Biological Research:
   • Study of cells, tissues, and microorganisms.

2. Medical Science:
   • Diagnosis of diseases, examination of body fluids, and surgical procedures.

3. Material Science:
   • Analysis of crystal structures, surface defects, and materials characterization.

4. Forensics:
   • Examination of trace evidence, such as hair, fibers, and fingerprints.

Applications of Telescopes

1. Astronomical Observations:
   • Study of celestial objects, such as stars, galaxies, and nebulae.

2. Space Exploration:
   • Observations of other planets, moons, asteroids, and comets.

3. Astrometry and Cosmology:
   • Determining positions and measuring distances of celestial objects.

4. Search for Extraterrestrial Life:
   • Scanning the sky for signs of intelligent beings.

Limitations of Microscopes

1. Limited Field of View:
   • Higher magnification often results in a narrower field of view.

2. Depth of Field:
   • Only a limited portion of the object appears in sharp focus at a time.

3. Optical Aberrations:
   • Spherical and chromatic aberrations may decrease image quality.

4. Specimen Preparations:
   • Certain specimens require staining and fixation, which may alter their natural state.

Limitations of Telescopes

1. Atmospheric Disturbances:
   • Turbulence in the Earth’s atmosphere causes image distortion.

2. Light Pollution:
   • Artificial lights interfere with observations, especially in urban areas.

3. Diffraction Limit:
   • Theoretical resolution is limited by the physics of light diffraction.

4. Inaccessibility:
   • Distant and remote objects may be challenging to observe and study.

Summary

• Microscopes and telescopes are indispensable tools in scientific research and exploration.
• Microscopes enable the study of minute details in various fields, from biology to materials science.
• Telescopes expand our understanding of the universe, bringing distant celestial objects closer to our eyes.
• Both instruments have their limitations, but continuous advancements allow us to overcome many of those constraints.