Space Communication — Physics

Q.1

WBCS Prelims 2015

Satellites provide information about

A. Forest and vegetative cover

B. Rivers and their courses

C. Advancing storms and cyclones

D. All of the above

Explanation

Why Correct: Remote sensing satellites use optical, infrared, and microwave sensors to monitor forest cover through vegetation indices like NDVI, track river courses via high-resolution imagery, and detect cyclones through cloud patterns and sea surface temperature data.
Distractor Analysis: Forest and vegetative cover monitoring uses multispectral imaging to assess biomass and deforestation. River course mapping employs synthetic aperture radar to penetrate cloud cover and track changes. Storm and cyclone tracking utilizes geostationary satellites for continuous weather observation and early warning systems.
Takeaway: India's INSAT series provides meteorological data, while Resourcesat and Cartosat support land and water resource management.

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Q.2

WBCS Prelims 2012

The first remote sensing satellite from India was :

A. P6

B. P4

C. IRS 1A

D. CARTOSAT 1

Explanation

Why Correct: IRS 1A launched on March 17, 1988 from Baikonur Cosmodrome, Kazakhstan aboard a Soviet Vostok rocket, marking India's first dedicated remote sensing satellite.
Distractor Analysis: P6 refers to IRS-P6 (Resourcesat-1) launched in 2003. P4 refers to IRS-P4 (Oceansat-1) launched in 1999. CARTOSAT-1 launched in 2005 as India's first stereoscopic imaging satellite.
Takeaway: Aryabhata, launched in 1975, was India's first satellite overall, while IRS 1A specifically initiated India's remote sensing program.

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Q.3

WBCS Prelims 2010

The minimum number of artificial satellites required for communication throughout the globe is

A. 1

B. 2

C. 3

D. 4

Explanation

Why Correct: Three geostationary satellites placed 120 degrees apart in equatorial orbit provide complete global coverage except for polar regions above 81 degrees latitude.
Distractor Analysis: One satellite covers only about one-third of Earth's surface. Two satellites leave significant gaps in coverage. Four satellites provide redundancy and better coverage but are not the theoretical minimum.
Takeaway: Geostationary satellites orbit at 35,786 km altitude with orbital period matching Earth's rotation, appearing stationary from ground.

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Q.4

WBPSC Miscellaneous Prelims 2018

What is the full form of SCM?

A. Standard Cosmological Model

B. Strong Cosmological Model

C. Stable Cosmological Model

D. Strict Cosmological Model

Explanation

Why Correct: SCM stands for Standard Cosmological Model, which describes the universe's large-scale structure and evolution based on the Big Bang theory, including dark energy and cold dark matter.
Distractor Analysis: 'Stable Cosmological Model' and 'Strict Cosmological Model' are not standard terms in cosmology. 'Strong Cosmological Model' is also not used. The only recognized acronym among these is Standard Cosmological Model.
Takeaway: The Standard Cosmological Model is also known as the Lambda-CDM model, where Lambda represents dark energy and CDM represents cold dark matter.

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Q.5

WBPSC Miscellaneous Prelims 2018

What is Li-Fi System?

A. It is a traditional computer chip.

B. It is a system relies on centralised light antennas.

C. It is a universal turing machine.

D. It is a single desktop computer.

Explanation

Why Correct: Li-Fi (Light Fidelity) is a wireless communication technology that uses light from LED bulbs to transmit data. It relies on centralized light antennas (LEDs) to modulate light intensity, which is detected by photodiodes.
Distractor Analysis: Option A: Traditional computer chip refers to microprocessors, not a communication system. Option C: Universal Turing machine is a theoretical computing model, unrelated to Li-Fi. Option D: Single desktop computer is a personal computer, not a communication system.
Takeaway: Li-Fi was coined by Harald Haas and uses visible light communication (VLC). It offers high-speed data transmission and is considered a complement to Wi-Fi.

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Q.6

WBPSC Miscellaneous Prelims 2010

Geostationary satellite revolves round the earth from

A. East to West

B. West to East

C. North to South

D. South to North

Explanation

Why Correct: Geostationary satellites orbit the Earth in the same direction as its rotation — from west to east — so they appear stationary relative to a point on the equator.
Distractor Analysis: East to west would be opposite to Earth's rotation, requiring a retrograde orbit. North to south and south to north describe polar orbits, which cross over the poles and are not geostationary.
Takeaway: A geostationary orbit has an orbital period of exactly 24 hours and is placed at an altitude of about 35,786 km above the equator, moving west to east.

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