General Principles in the Working of Telescope, Microscope
General Principles in the Working of Telescope, Microscope MCQ Questions
7.
Which telescope is best for observing distant galaxies?
ANSWER :
C. Infrared telescope
Approach
The question asks which type of telescope is best suited for observing distant galaxies. Distant galaxies are characterized by significant redshift due to the expansion of the universe, meaning their emitted light is shifted towards longer wavelengths. We need to consider which part of the electromagnetic spectrum is most effective for observing these redshifted objects and which telescope type specializes in that.
Step-by-step
- Understanding Redshift: As galaxies move away from us due to the expansion of the universe, the light they emit gets stretched to longer wavelengths. This phenomenon is called cosmological redshift. For very distant galaxies, light originally emitted in the visible or ultraviolet spectrum can be redshifted into the infrared part of the electromagnetic spectrum.
- Penetrating Dust: Infrared radiation also has the advantage of being able to penetrate cosmic dust clouds more effectively than visible light. Many distant galaxies are obscured by dust, making infrared observation crucial.
- Atmospheric Absorption: Earth's atmosphere absorbs much of the infrared radiation. Therefore, infrared telescopes are often placed in space or at very high, dry altitudes to minimize atmospheric interference.
- Comparing Telescope Types:
- Optical telescopes observe visible light, which is heavily redshifted for distant galaxies.
- Radio telescopes observe very long wavelengths (radio waves), which are useful for different phenomena but not typically for imaging the main stellar populations of distant, redshifted galaxies as effectively as infrared.
- Infrared telescopes are specifically designed to detect infrared radiation, making them ideal for observing objects whose light has been redshifted into this spectrum and for penetrating dust.
Correct Option:
C) Infrared telescope is the best choice because light from very distant galaxies is significantly redshifted into the infrared spectrum, and infrared radiation can penetrate cosmic dust more effectively than visible light.
Incorrect Options
- A) Radiotelescope — While radio telescopes are excellent for observing certain phenomena (like cold gas, pulsars, and active galactic nuclei), they are not the primary choice for imaging the stellar populations of distant, redshifted galaxies, which are better observed in the infrared.
- B) Refracting telescope — This is a type of optical telescope that uses lenses. Like other optical telescopes, it primarily observes visible light, which is not ideal for highly redshifted distant galaxies.
- D) Optical telescope — Optical telescopes observe visible light. For very distant galaxies, the visible light they emit is redshifted out of the visible spectrum and into the infrared, making optical telescopes less effective for these objects.
8.
What is the advantage of space telescopes?
A.
Avoid atmospheric distortion
ANSWER :
A. Avoid atmospheric distortion
Approach
The question asks about the primary advantage of space telescopes. We need to consider the challenges faced by ground-based telescopes and how placing telescopes in space mitigates these issues.
Step-by-step
- Understanding Ground-based Telescopes: Telescopes on Earth's surface must look through the atmosphere.
- Atmospheric Effects: The Earth's atmosphere contains gases, dust, and water vapor. These components absorb, scatter, and refract light and other electromagnetic radiation coming from celestial objects. This causes blurring, twinkling (scintillation), and distortion of images, making it difficult to resolve fine details. Different wavelengths of light are also absorbed to varying degrees, limiting the observable spectrum from the ground.
- Advantage of Space Telescopes: By placing telescopes in orbit above the Earth's atmosphere, they can observe celestial objects without these atmospheric interferences. This allows for much clearer, sharper images and the ability to detect a broader range of electromagnetic radiation (like X-rays, gamma rays, and much of the infrared and ultraviolet spectrum) that would otherwise be blocked by the atmosphere.
Correct Option:
A) Avoid atmospheric distortion — This is the primary and most significant advantage of space telescopes. By operating above the Earth's atmosphere, they are not affected by atmospheric blurring, absorption, and scattering, leading to much clearer images and access to a wider range of the electromagnetic spectrum.
Incorrect Options
- B) Easy to maintain — Space telescopes are extremely difficult and expensive to maintain. Once launched, repairs or upgrades require complex and costly space missions, unlike ground-based telescopes which can be accessed relatively easily for maintenance.
- C) Lower cost — Space telescopes are significantly more expensive to design, build, launch, and operate compared to ground-based telescopes. The cost of launching a payload into space is enormous, and the engineering challenges are far greater.
- D) Portable — Space telescopes are not portable in the conventional sense. They are launched into specific orbits and remain there, whereas portability usually implies ease of movement from one location to another on Earth.
9.
What is the largest optical telescope in the world?
A.
Hubble Space Telescope
B.
Gran Telescopio Canarias
ANSWER :
B. Gran Telescopio Canarias
Approach
The question asks to identify the largest optical telescope in the world. This requires knowledge of current astronomical observatories and their primary mirror sizes, which is a common topic in general science and current affairs sections of competitive exams.
Step-by-step
- Understand what an optical telescope is: It's a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct viewing or to make a photograph.
- The size of an optical telescope is primarily determined by the diameter of its primary mirror (for reflecting telescopes) or lens (for refracting telescopes). Larger mirrors/lenses collect more light, allowing for observations of fainter objects and higher resolution.
- Recall or research the largest optical telescopes currently in operation.
- Compare the primary mirror sizes of the telescopes listed in the options.
The Gran Telescopio Canarias (GTC) has a primary mirror composed of 36 hexagonal segments that together act as a single mirror with a diameter of 10.4 meters. This makes it the largest single-aperture optical telescope in the world.
Correct Option: B) Gran Telescopio Canarias is currently the largest single-aperture optical telescope in the world, with a primary mirror diameter of 10.4 meters.
Incorrect Options
- A) Hubble Space Telescope: While famous and highly productive, the Hubble Space Telescope is a space telescope with a primary mirror of 2.4 meters. It is not the largest optical telescope, especially when compared to ground-based observatories.
- C) Keck Observatory: The Keck Observatory consists of two telescopes, Keck I and Keck II, each with a primary mirror of 10 meters in diameter. While very large and among the biggest, the Gran Telescopio Canarias is slightly larger at 10.4 meters.
- D) Chandra Telescope: The Chandra X-ray Observatory is a space telescope designed to detect X-ray emissions from hot regions of the universe. It is an X-ray telescope, not an optical telescope, and therefore does not fit the criteria of the question.
10.
What is the unit of measurement for the resolving power of a telescope?
Approach
The question asks for the unit of measurement for the resolving power of a telescope. Resolving power refers to the ability of an optical instrument to distinguish between two closely spaced objects. This ability is typically measured as an angular separation.
Step-by-step
- Understanding Resolving Power: Resolving power in astronomy, particularly for telescopes, is the ability to see fine details or to separate two distinct objects that are very close together in the sky.
- Angular Separation: Since celestial objects are at vast distances, their apparent separation from our perspective is measured as an angle. A smaller angle indicates better resolving power, meaning the telescope can distinguish objects that are closer together.
- Units of Angular Measurement: Angles can be measured in degrees, radians, arcminutes, or arcseconds. For the very small angles involved in astronomical resolution, arcseconds are the most commonly used unit. One degree is equal to 60 arcminutes, and one arcminute is equal to 60 arcseconds. Therefore, one degree is equal to 3600 arcseconds.
- Rayleigh Criterion: The theoretical limit of resolving power for a circular aperture (like a telescope lens or mirror) is given by the Rayleigh criterion, which states that the minimum angular separation \(\theta\) (in radians) that can be resolved is:\[ \theta = 1.22 \frac{\lambda}{D} \]where \(\lambda\) is the wavelength of light and \(D\) is the diameter of the aperture. When converted to arcseconds, this angular separation represents the resolving power.
Correct Option:
B) Arcseconds — Resolving power is an angular measurement, indicating the smallest angle between two objects that a telescope can distinguish. Arcseconds are the standard unit for expressing these very small angles in astronomy.
Incorrect Options
- A) Meters — Meters are a unit of length or distance, not angular separation. While the diameter of a telescope's aperture (measured in meters) affects resolving power, resolving power itself is not measured in meters.
- C) Decibels — Decibels are a logarithmic unit used to express the ratio of two values of a power or root-power quantity, often used in acoustics or electronics to measure sound intensity or signal strength. They are not related to angular resolution.
- D) Watts — Watts are a unit of power, representing the rate at which energy is transferred or converted. This unit is used for measuring the brightness or energy output of celestial objects, not the resolving power of a telescope.
11.
Which type of telescope uses mirrors to gather and focus light?
ANSWER :
A. Reflecting telescope
Approach
The question asks to identify the type of telescope that uses mirrors to gather and focus light. This requires knowledge of the basic principles and components of different telescope types.
Step-by-step
- Understand the function of a telescope: A telescope's primary function is to collect electromagnetic radiation (light) from distant objects and bring it to a focus, allowing for magnification and detailed observation.
- Consider the components for light collection and focusing: Telescopes achieve this using either lenses or mirrors.
- Recall the definition of a reflecting telescope: A reflecting telescope, also known as a reflector, uses one or more curved mirrors to reflect light and form an image. The primary mirror gathers the light.
- Recall the definition of a refracting telescope: A refracting telescope, or refractor, uses lenses to bend (refract) light to form an image.
- Recall the definition of a radiotelescope: A radiotelescope detects radio waves, which are a form of electromagnetic radiation, using large dish antennas, not optical mirrors.
- Recall the definition of an infrared telescope: An infrared telescope is designed to detect infrared radiation, often using mirrors, but its defining characteristic is the type of radiation it detects, not exclusively the use of mirrors for visible light. However, when speaking generally about telescopes that use mirrors for *light* (implying visible light or a broader optical spectrum), the term "reflecting telescope" is most appropriate.
- Match the description to the options: The description "uses mirrors to gather and focus light" directly corresponds to the definition of a reflecting telescope.
Correct Option: A) A reflecting telescope uses mirrors (typically a large primary mirror) to gather and focus light from celestial objects. This design helps overcome chromatic aberration common in refracting telescopes and allows for much larger apertures.
Incorrect Options
- B) Refracting telescope: This type of telescope uses lenses, not mirrors, to gather and focus light. Lenses bend (refract) light to form an image.
- C) Radiotelescope: A radiotelescope is designed to detect radio waves, which are a different part of the electromagnetic spectrum than visible light. It typically uses large dish antennas, not optical mirrors, to collect these waves.
- D) Infrared telescope: While many infrared telescopes do use mirrors to collect infrared radiation, their defining characteristic is the type of radiation they detect (infrared), not solely the use of mirrors for general light collection. The most direct answer for a telescope using mirrors to gather and focus "light" (in the general sense, often implying visible) is a reflecting telescope.
12.
Who first used a telescope to observe the night sky?
ANSWER :
A. Galileo Galilei
Approach
The question asks to identify the individual who first utilized a telescope for astronomical observations of the night sky. This requires knowledge of key figures in the history of astronomy and their contributions.
Step-by-step
- The telescope was invented in the Netherlands around 1608.
- Galileo Galilei, an Italian astronomer, physicist, and engineer, heard about the invention in 1609.
- He quickly improved upon the design and built his own telescopes, achieving higher magnifications than the original Dutch models.
- Galileo was the first person to systematically point a telescope towards the night sky and make detailed observations, which led to groundbreaking discoveries.
Correct Option: A) Galileo Galilei is widely credited with being the first to use a telescope for astronomical observations. His observations, starting in 1609, included the phases of Venus, the four largest moons of Jupiter (now known as the Galilean moons), sunspots, and the mountains and craters on the Moon. These observations provided strong evidence supporting the heliocentric model of the solar system.
Incorrect Options
- B) Tycho Brahe was a Danish nobleman, astronomer, and writer who made accurate and comprehensive astronomical observations without the aid of a telescope. He lived from 1546 to 1601, preceding the invention of the telescope.
- C) Johannes Kepler was a German astronomer, mathematician, and astrologer. He is best known for his laws of planetary motion. While he used observations made by Tycho Brahe, and later corresponded with Galileo, Kepler himself did not invent or first use the telescope for astronomical observations. He did, however, improve the theory of the telescope.
- D) Nicolaus Copernicus was a Renaissance-era mathematician and astronomer who formulated a model of the universe that placed the Sun rather than Earth at its center (heliocentrism). He lived from 1473 to 1543, long before the invention of the telescope. His work was based on naked-eye observations and mathematical calculations.
