Miscellaneous — Physics

Q.1

WBCS Prelims 2004

In the solar spectrum Fraunhofer lines are seen in the sodium D wavelength This proves

A. there is no sodium in the sun

B. there is no sodium in the solar atmosphere

C. there is no sodium in the sun's interior

D. there is sodium in the solar atmosphere

Explanation

Why Correct: Fraunhofer lines are absorption lines at specific wavelengths, caused by elements in the Sun's cooler outer atmosphere absorbing radiation from the hotter interior.
Distractor Analysis: Sodium D lines at 589.0 nm and 589.6 nm specifically indicate sodium presence. The lines prove sodium exists in the solar atmosphere, not its absence.
Takeaway: Fraunhofer lines identify elemental composition of stellar atmospheres; each element has unique absorption wavelengths.

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Q.2

WBCS Prelims 2002

Lightning discharges induce rain formation. This is because they cause

A. Nitrogen and oxygen of the air to combine

B. Some gas molecules to ionize

C. The electrical discharge active the H2O molecules

D. They induce photochemical reactions.

Explanation

Why Correct: Lightning ionizes atmospheric gases, producing charged particles that act as condensation nuclei for water vapor to form raindrops.
Distractor Analysis: Nitrogen and oxygen combine to form nitrogen oxides, not rain. Electrical discharge does not activate H2O molecules directly. Photochemical reactions require sunlight, not lightning.
Takeaway: The Bergeron-Findeisen process describes how ice crystals grow at the expense of supercooled water droplets in clouds, another rain formation mechanism.

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Q.3

WBCS Prelims 2012

Aerial photographs are studied with the help of :

A. Microscope

B. Stereoscope

C. Parallax bar

D. Theodolite

Explanation

Why Correct: Stereoscopes create three-dimensional depth perception by presenting slightly offset images to each eye, essential for interpreting aerial photographs' terrain and elevation.
Distractor Analysis: Microscopes magnify tiny objects, not large-scale aerial images. Parallax bars measure height differences between points on stereo pairs but do not provide the visual interpretation itself. Theodolites measure horizontal and vertical angles in land surveying.
Takeaway: In photogrammetry, stereoscopes work with overlapping aerial photographs taken from different positions along a flight line to create stereo models.

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