General Principles in the Working of Telescope, Microscope
General Principles in the Working of Telescope, Microscope MCQ Questions
13.
What is the primary reason telescopes are placed on mountains?
A.
To avoid light pollution
B.
To get closer to space
C.
To reduce atmospheric distortion
ANSWER :
C. To reduce atmospheric distortion
Approach
The question asks for the primary reason why telescopes are placed on mountains. This relates to optimizing observational conditions for astronomical research. We need to consider the factors that affect the quality of astronomical observations from Earth's surface.
Step-by-step
- Understanding Atmospheric Effects: Earth's atmosphere, while vital for life, significantly distorts light from celestial objects. This distortion is caused by variations in temperature, pressure, and humidity, which lead to changes in the refractive index of the air.
- Impact on Astronomical Observations: These atmospheric variations cause starlight to twinkle (scintillation) and blur images (seeing). This reduces the clarity and resolution of images captured by telescopes.
- Advantage of High Altitudes: Mountains offer higher altitudes where the atmosphere is thinner, drier, and more stable. By placing telescopes on high mountains, astronomers can reduce the amount of atmosphere the light has to travel through before reaching the telescope.
- Minimizing Distortion: A thinner and more stable atmosphere means less turbulence and fewer refractive index variations, thus significantly reducing atmospheric distortion and improving the "seeing" conditions for astronomical observations.
Correct Option: C) To reduce atmospheric distortion. Placing telescopes on mountains helps to get above a significant portion of the Earth's atmosphere, which is responsible for blurring and distorting astronomical images due to turbulence and varying refractive indices.
Incorrect Options
- A) To avoid light pollution. While light pollution is a significant problem for ground-based astronomy, and mountains often provide isolation from city lights, it is not the primary reason. Telescopes can be placed in remote areas at lower altitudes to avoid light pollution, but they would still suffer from atmospheric distortion.
- B) To get closer to space. Even the highest mountains are only a few kilometers above sea level, which is negligible compared to the vast distances to celestial objects or even the thickness of Earth's atmosphere (which extends hundreds of kilometers). This slight increase in altitude does not significantly reduce the physical distance to space.
- D) To reduce cost. Building and maintaining observatories on remote mountain tops is typically very expensive due to logistical challenges, extreme weather conditions, and the need for specialized infrastructure. Therefore, reducing cost is definitely not a reason.
14.
What is the main purpose of an optical telescope?
A.
To detect gravitational waves
B.
To detect visible light
ANSWER :
B. To detect visible light
Approach
The question asks for the primary function of an optical telescope. This requires understanding the basic principles of different types of telescopes and the electromagnetic spectrum.
Step-by-step
- Understand what an optical telescope is: An optical telescope is a type of telescope that gathers and focuses light, primarily from the visible part of the electromagnetic spectrum, to create a magnified image for direct viewing, photography, or data analysis.
- Consider the term "optical": The word "optical" directly refers to light, specifically visible light, which is the portion of the electromagnetic spectrum that the human eye can perceive.
- Relate to the electromagnetic spectrum: The electromagnetic spectrum includes various forms of radiation like radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Different telescopes are designed to detect different parts of this spectrum.
- Evaluate the options based on the definition: An optical telescope is inherently designed to work with visible light. Other forms of radiation require different detection methods and telescope designs (e.g., radio telescopes for radio waves, X-ray telescopes for X-rays).
Correct Option: B) To detect visible light. Optical telescopes are specifically designed to collect and focus visible light from celestial objects, allowing us to observe them.
Incorrect Options
- A) To detect gravitational waves — Gravitational waves are ripples in spacetime, not electromagnetic radiation. They are detected by specialized instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory), not optical telescopes.
- C) To detect gamma rays — Gamma rays are high-energy electromagnetic radiation. Gamma-ray telescopes use different principles, such as Compton scattering or pair production, and are typically space-based due to atmospheric absorption.
- D) To detect X-rays — X-rays are also high-energy electromagnetic radiation. X-ray telescopes use grazing incidence mirrors because X-rays would pass through conventional mirrors. These telescopes are also typically space-based.
15.
What is the largest radio telescope in the world?
Approach
The question asks to identify the largest radio telescope in the world. This requires knowledge of prominent radio astronomy facilities and their characteristics, specifically their size.
Step-by-step
- Recall or research the major radio telescopes globally.
- Compare their primary mirror or dish diameters/sizes.
- Identify the one with the largest effective aperture or collecting area.
- The Five-hundred-meter Aperture Spherical Telescope (FAST) in China is known for its immense 500-meter diameter dish, making it the largest single-dish radio telescope.
Correct Option: A) FAST (China) is the Five-hundred-meter Aperture Spherical Telescope, located in Guizhou, China. With a dish diameter of 500 meters, it is currently the world's largest single-dish radio telescope and the second-largest aperture in the world after Russia's RATAN-600 (which is a circular array, not a single dish).
Incorrect Options
- B) Arecibo Observatory: Located in Puerto Rico, the Arecibo telescope had a fixed spherical reflector dish 305 meters in diameter. While historically significant and very large, it was smaller than FAST and unfortunately collapsed in 2020.
- C) Green Bank Telescope: The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, USA, is the world's largest fully steerable radio telescope, with a dish diameter of 100 meters. While impressive for its steerability, its size is considerably less than FAST.
- D) ALMA (Chile): The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes located in the Atacama Desert of northern Chile. It is an array of multiple dishes working together, not a single large dish. Its individual antennas are 12 meters and 7 meters in diameter, which are much smaller than FAST's single dish.
16.
What does the term "aperture" in a telescope refer to?
B.
Diameter of the lens/mirror
ANSWER :
B. Diameter of the lens/mirror
Approach
The question asks for the definition of "aperture" in the context of a telescope. Understanding the basic components and functions of a telescope is key to answering this question.
Step-by-step
- Define Aperture: In optics, especially for telescopes, the aperture refers to the effective diameter of the light-gathering element, which is typically the primary lens (in a refractor telescope) or the primary mirror (in a reflector telescope).
- Function of Aperture: The aperture determines two crucial characteristics of a telescope:
- Light-gathering power: A larger aperture collects more light, allowing fainter objects to be observed.
- Resolving power: A larger aperture provides better resolution, meaning it can distinguish finer details and separate closely spaced objects.
- Evaluate Options: Based on this understanding, we can evaluate the given options.
Correct Option:
B) Diameter of the lens/mirror — This accurately defines aperture. The diameter of the primary optical component (lens or mirror) is what determines how much light the telescope can collect and its ability to resolve fine details.
Incorrect Options
- A) Lens curvature — While the curvature of a lens or mirror is critical for its focal length and image formation, it is not what the term "aperture" specifically refers to. Aperture is about the size of the opening, not its shape or curvature.
- C) Focal length — Focal length is the distance from the lens or mirror to the point where light rays converge to form a sharp image. It affects magnification and the field of view, but it is distinct from the aperture.
- D) Magnification — Magnification is the ability of the telescope to make an object appear larger. It is determined by the ratio of the focal length of the objective lens/mirror to the focal length of the eyepiece, not directly by the aperture itself, although aperture influences the quality of the magnified image.
17.
What is the focal length of a telescope?
A.
Distance between lens and image
C.
Power of magnification
ANSWER :
A. Distance between lens and image
Approach
The question asks for the definition of the focal length of a telescope. We need to recall the basic principles of optics and how lenses/mirrors form images, specifically in the context of a telescope.
Step-by-step
- A telescope uses lenses or mirrors to gather light and form an image of distant objects.
- The focal length of a lens or mirror is a fundamental property that determines where parallel rays of light (from a distant object) converge to form a real image, or from where they appear to diverge after refraction/reflection.
- In a telescope, the objective lens (or primary mirror) collects light and forms an intermediate image. The distance from the optical center of this objective to where the image is formed is its focal length.
- Similarly, the eyepiece lens has its own focal length, which determines how it magnifies this intermediate image.
- Therefore, the focal length is directly related to the distance at which an image is formed by the optical components.
Correct Option: A) Distance between lens and image
The focal length of a lens or mirror is defined as the distance from the optical center (or pole for a mirror) to the principal focus, which is the point where parallel rays of light converge after passing through the lens or reflecting off the mirror. This point is where the real image of a very distant object is formed. Thus, it represents the distance between the optical element (lens/mirror) and the image formed by it for distant objects.
Incorrect Options
- B) Width of the mirror — The width (or diameter) of the mirror is its aperture. While aperture is an important characteristic of a telescope (affecting light-gathering power and resolution), it is not the focal length.
- C) Power of magnification — Magnification power is a ratio determined by the focal lengths of the objective and eyepiece lenses (\(M = f_o / f_e\)). It is a consequence of focal length, not the definition of focal length itself.
- D) Resolution capability — Resolution capability refers to the telescope's ability to distinguish between two closely spaced objects. It is primarily determined by the aperture of the objective lens/mirror and the wavelength of light, not directly by the focal length alone.
18.
Which planet was discovered using a telescope?
Approach
The question asks to identify the planet that was discovered using a telescope. This requires knowledge of the history of planetary discoveries and the tools used for observation.
Step-by-step
- Understanding pre-telescopic planets: Planets like Mercury, Venus, Mars, Jupiter, and Saturn are visible to the naked eye and have been known since ancient times. Their existence predates the invention of the telescope.
- The invention of the telescope: The telescope was invented in the early 17th century, revolutionizing astronomy.
- Discovery of Uranus: William Herschel discovered Uranus on March 13, 1781, using a telescope. Initially, he thought it was a comet or a star, but further observations confirmed it as a new planet. This marked the first discovery of a planet using a telescope.
- Discovery of Neptune: Neptune was discovered much later, in 1846, based on mathematical predictions by Urbain Le Verrier and John Couch Adams, and then observed telescopically by Johann Galle. While a telescope was used for its observation, its discovery was primarily driven by gravitational perturbation calculations, and it was discovered after Uranus.
Therefore, Uranus was the first planet discovered with the aid of a telescope.
Correct Option: C) Uranus was discovered by William Herschel in 1781 using a telescope. This was the first planet whose discovery was attributed to telescopic observation.
Incorrect Options
- A) Mars — Mars is one of the five planets (Mercury, Venus, Mars, Jupiter, Saturn) visible to the naked eye and has been known since antiquity. Its discovery does not involve a telescope.
- B) Neptune — Neptune was discovered in 1846, after Uranus. Its discovery was based on mathematical predictions of its gravitational effect on Uranus, and then observed telescopically. While a telescope was used, it was not the *first* planet discovered using this instrument, nor was its discovery purely accidental like Uranus's.
- D) Jupiter — Jupiter is also one of the planets visible to the naked eye and has been known since ancient times. Its discovery does not involve a telescope.
