Explanation

• The audible range of a normal human ear is 20 Hz to 20,000 Hz (20 kHz).
• Below 20 Hz: Infrasound
• Above 20 kHz: Ultrasound
• Unit of frequency: Hertz (Hz)

Last verified on 23-06-2026

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

• Vitamin D is essential for healthy bones.
• Its deficiency leads to Rickets in children and Osteomalacia in adults.
• Sunlight is the best natural source of Vitamin D.

Additional information:

Deficiency effects:

• Bone pain
• Weak bones
• Skeletal deformities

Other Vitamin Deficiencies:

• Vitamin A: Night blindness
• Vitamin C: Scurvy
• Vitamin B7 (Biotin): Hair fall

Last verified on 17-01-2026

Explanation

• Almost all the mass of an atom is concentrated in its nucleus.
• The nucleus contains protons and neutrons, which are much heavier than electrons.
• Electrons revolve around the nucleus but contribute very little to atomic mass.
• The nucleus is located at the center of the atom.
• Ernest Rutherford discovered the nucleus through the gold foil experiment in 1911.

Last verified on 09-05-2026

Explanation

• Earth water coverage: 71%
• Land area: 29%
• Ocean water: 97% of total water
• Fresh water: 3% of total water
• Largest ocean: Pacific Ocean

Last verified on 10-04-2026