Explanation

• Solar plates consist of photovoltaic (PV) cells.
• PV cells convert sunlight directly into electrical energy.
• These cells work on the photovoltaic effect. 
• They are usually made of semiconductor materials like silicon.

Additional information:

• Discovered photovoltaic effect: 1839 by Edmond Becquerel

Common types of solar cells:

1. Monocrystalline silicon cells
2. Polycrystalline silicon cells
3. Thin-film solar cells

Last verified on 23-06-2026

Explanation

• On average, the human body contains about 60–70% water.
• Adult males: 60–65%
• Adult females: 50–60%
• Infants: ~75%
• Main functions: transport, digestion, temperature regulation

Last verified on 23-06-2026

Explanation

• Rectified spirit contains about 95% ethyl alcohol.
• It is highly purified alcohol obtained by repeated distillation.
• The remaining percentage is usually water.
• It is used in pharmaceuticals, laboratories, and industrial processes.

Last verified on 23-06-2026

Explanation

• Hydrophytes have poorly developed roots.
• Because they live in water and can absorb water directly from their surroundings.

Additional information:

Key Characteristics of Hydrophytes:

• Reduced xylem tissue
• Large air spaces in tissues (aerenchyma)
• Thin or absent cuticle
• Flexible stems and leaves

Examples include water lily and Hydrilla.

Last verified on 23-06-2026

Explanation

• The audible range of a normal human ear is 20 Hz to 20,000 Hz (20 kHz).
• Sounds below this range are called infrasound,
• Sounds above it are called ultrasound. 
• Lower limit: 20 Hz (deep rumbles)
• Upper limit: 20,000 Hz (high-pitched squeaks)

Additional information

• Adult change: The upper limit often drops to 15,000–17,000 Hz as people get older. 
• Unit of frequency: Hertz (Hz)

Last updated 27-07-2026 by NA

Explanation

• Damage to alveoli due to smoking leads to reduced gas exchange efficiency in the lungs.
• Alveoli are tiny air sacs where oxygen enters blood and carbon dioxide is removed.
• Smoking destroys alveolar walls, reducing surface area for gas exchange.
• This causes breathing problems and diseases like emphysema and COPD.

Last verified on 22-06-2026

Explanation

• The mass of a proton is approximately 1836 times greater than the mass of an electron.
• A proton is a positively charged particle found in the nucleus of an atom.
• It has almost the same mass as a neutron (slightly less).
• Electrons are much lighter compared to protons.

Last verified on 22-06-2026

Explanation

• Neon gas was discovered by William Ramsay and Morris Travers in 1898.
• It was found during the study of liquefied air and noble gases.
• Neon is a noble gas.
• It is chemically inert (does not react easily).
• It is famous for producing bright reddish-orange light in neon signs.
• It is present in very small amounts in Earth’s atmosphere.

Last verified on 21-06-2026

Explanation

• Theory proposed by: Charles Darwin
• Book published: 1859
• Book name: On the Origin of Species
• Key concept: Natural Selection
• Voyage that inspired him: HMS Beagle expedition (1831–1836)

Last verified on 21-06-2026

Explanation

• The density of gases increases when pressure is increased because gas molecules come closer together.
• Density is the mass per unit volume of a substance.
• When pressure increases, the volume of gas decreases (at constant temperature), causing density to increase.
• This relationship follows Boyle’s Law.

Last verified on 21-06-2026