Explanation

Surface area = 4πr², Volume = 4/3πr³.  

Surface area is just derivative of volume w.r.t r.

2πr is circumference of a circle, not volume at all.

Last verified on 07-06-2026

Explanation

• Smog is a form of air pollution formed by smoke + fog.
• It mainly occurs in big cities due to vehicle and factory emissions.
• It reduces visibility and causes breathing problems.
• Smog is a serious environmental and health hazard.

Last verified on 06-06-2026

Explanation

• According to scientists, the universe has about 100 billion galaxies.
• Earlier estimates from the Hubble Space Telescope suggested similar numbers.
• Modern studies show it may be between 100–200 billion galaxies.
• Some older estimates even suggested up to 2 trillion galaxies (later revised).

Last verified on 06-06-2026

Explanation

• Oceans play the most important role in regulating Earth’s temperature and climate.
• They absorb heat from the Sun and distribute it across the planet.
• Ocean currents control weather patterns globally.
• They help maintain Earth’s temperature balance.

Last verified on 06-06-2026

Explanation

• Mangrove forests act as barriers against cyclones.
• Mangroves reduce erosion by trapping sediments, stabilizing the coastal zone and thus protecting the coast from storm surges and cyclones.
• Mangroves in Pakistan are found along the coastline of Sindh and Balochistan.

Last verified on 06-06-2026

Explanation

• Over-damping occurs when damping force is very large.
• The system returns to equilibrium without oscillating.
• Because of strong resistance, motion becomes very slow.
• It takes more time compared to critical damping.

Last verified on 05-06-2026

Explanation

• Physical pendulum depends on moment of inertia (I) and distance (d) from pivot to center of mass.
• Time period increases when mass is farther from pivot (larger d).
• Standard formula is T = 2π√(I/Mgd).

Last verified on 05-06-2026

Explanation

• Zener diode is mainly used as a constant voltage regulator.
• It operates in the reverse breakdown region.
• In this region, voltage remains almost constant even if current changes.

Last verified on 05-06-2026

Explanation

• The average distance covered by an alpha particle in air before losing its ionizing power is called its range.
• Alpha particles lose energy continuously while moving through air.
• They stop ionizing after traveling a certain distance.
• This stopping distance is not straight-line path always due to collisions.

Last verified on 05-06-2026

Explanation

• Lyman series lies in the ultraviolet (UV) region of hydrogen spectrum.
• It is produced when an electron falls to the first energy level (n = 1).
• These transitions release high-energy photons.

Additional information:

• Balmer series lies in the visible region.
• Paschen and Brackett are in infrared.

Last verified on 05-06-2026