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

• 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

Explanation

• The movement of water from higher water potential to lower water potential is called osmosis.
• It occurs through a semi-permeable membrane.
• Only water molecules move in osmosis.
• It is a passive process (no energy required).

Last verified on 18-06-2026

Explanation

• The human body contains about 65% oxygen by mass.
• Oxygen is the most abundant element in the human body.
• It is mainly present in water (H₂O) and organic compounds.
• It is essential for respiration and energy production.

Additional information:

• Carbon: ~18%
• Hydrogen: ~10%
• Nitrogen: ~3%
• Other elements: ~4% (calcium, phosphorus, etc.)

Last verified 09-06-2026

Explanation

When white light passes through a prism, it splits into 7 colors, forming a spectrum known as a rainbow:

1. Red
2. Orange
3. Yellow
4. Green
5. Blue
6. Indigo
7. Violet

The separation of visible light into its different colours is known as dispersion.

Last verified on 08-06-2026

Explanation

• Sublimation is the direct transition of a solid into a gas without passing through the liquid phase.

Additional information:

Some common sublimating substances:

• Dry ice (CO₂) – solid → gas
• Iodine crystals – solid → violet gas
• Camphor – solid → vapor
• Naphthalene (mothballs) – solid → gas
• Ammonium chloride – solid → gas

Last verified on 13-03-2026

Explanation

• Pressure in gases is due to the collision of gas molecules with the walls of the container.
• Gas molecules are in constant random motion.
• They continuously strike the container walls.
• These collisions create force per unit area (pressure).
• More collisions mean higher pressure.

Last verified on 08-06-2026

Explanation

• Photosynthesis produces glucose and oxygen.
• Green plants use sunlight, water, and carbon dioxide.
• This process occurs in chloroplasts using chlorophyll.
• Glucose is used as food for energy and growth.
• Oxygen is released as a byproduct into the atmosphere.

Last verified on 10-03-2026

Explanation

• Short-sightedness is called Myopia.
• It is corrected by a concave lens.
• This lens is thin in the center and thick at edges.
• It helps light focus on the retina correctly.
• Without correction, distant objects look blurred.

Additional information:

• Long-sightedness is called Hypermetropia.
• It is corrected by a convex lens.
• This lens is thick in the center and thin at edges.
• It helps light focus on the retina properly.
• Without correction, near objects look blurred.

Last verified on 07-06-2026

Explanation

• Proteins are called body-building foods.
• They help in growth, repair of tissues, and muscle development.
• They are essential for maintaining and rebuilding body cells.
• They are made of amino acids, the building blocks of the body.
• Deficiency of protein can lead to weak muscles and poor growth.

Last verified on 06-05-2026