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 retina is the light-sensitive layer located at the back of the human eye.
• It contains special cells called rods and cones that detect light and color.
• These cells convert light into electrical signals.
• The signals are then sent to the brain through the optic nerve to produce vision.

Last verified on 11-03-2026

Explanation

• The part of the eye that controls the amount of light entering is the Iris.
• It adjusts the size of the pupil according to light intensity.
• In bright light, it reduces light entry; in dim light, it allows more light in.
• This process protects the retina and helps clear vision.

Last verified on 17-05-2026

Explanation

• Mars is known as the Red Planet due to its reddish appearance.
• Its surface contains iron oxide (rust) which gives it a red color.
• It is the 4th planet from the Sun in the solar system.
• Mars has two small moons: Phobos and Deimos.
• Mars is often called the “planet of future exploration”.

Last verified on 12-06-2026

Explanation

• The SI unit of electrical resistance is Ohm (Ω).
• It measures how much a material opposes the flow of electric current.
• Higher resistance means less current flows.
• It is defined by V = IR (Ohm’s Law).
• 1 Ohm = 1 Volt per Ampere.

Last verified on 10-06-2026

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

• Mitochondria are called the powerhouse of the cell.
• Because they produce Adenosine Triphosphate (ATP).
• ATP is the energy currency of the cell.
• ATP provides energy for different cellular activities such as movement, growth, and transport.
• Energy is produced through aerobic cellular respiration using oxygen and الغذائی molecules.
• They are found in the cytoplasm of most eukaryotic cells.
• Richard Altmann first described mitochondria in 1890.

Main Parts of a Cell:

1. Cell membrane → Outer protective layer
2. Nucleus → Controls cell activities
3. Cytoplasm → Jelly-like material between membrane and nucleus

Last verified on 09-05-2026