Explanation

• The velocity of a wave depends on its wavelength and frequency.
• Formula: v = λ × f, where λ is wavelength and f is frequency.
• This applies to sound waves, light waves, and water waves.
• Higher frequency or longer wavelength increases the wave’s velocity if the medium is constant.

Last verified on 17-03-2026

Explanation

• An echo is a sound that reflects off a surface and is heard again.
• It occurs when sound waves bounce back from a distant surface like a wall or mountain.
• Echoes are common in caves, valleys, and empty halls.
• The reflected sound is perceived after a short delay.

Last verified on 17-03-2026

Explanation

• Gravity pulls objects toward the center of the Earth.
• To lift or move an object against gravity, a force equal to or greater than gravitational force is needed.
• This force allows objects to rise or stay in motion vertically.

Last verified on 17-03-2026

Explanation

• When a marker is held and released, gravity pulls it downward.
• If there was an initial upward push, the upward force can be greater than the downward force momentarily.
• The marker accelerates until gravity slows it and pulls it back down.
• This explains the initial upward motion before falling.

Last verified on 17-03-2026

Explanation

• Total internal reflection occurs when light travels from a denser medium to a rarer medium.
• The angle of incidence must be greater than the critical angle for the two media.
• Light is completely reflected back into the denser medium instead of refracting.
• Common examples: optical fibers, diamonds, and mirages.

Last verified on 17-03-2026

Explanation

• The sky appears blue due to Rayleigh scattering of sunlight by the atmosphere.
• Shorter wavelengths like blue light scatter more than longer wavelengths (red, yellow).
• The scattered blue light reaches our eyes, making the sky appear blue.
• Red light is less scattered and passes through the atmosphere.

Last verified on 17-03-2026

Explanation

• Ions are charged particles formed when an atom gains or loses electrons.
• Loss of electrons creates a positively charged ion (cation).
• Gain of electrons creates a negatively charged ion (anion).

Last verified on 17-03-2026

Explanation

• Polyvinyl chloride (PVC) is a widely used synthetic polymer.
• It is a solid plastic material at room temperature.
• PVC is used in pipes, bottles, cables, and packaging.
• It is durable, lightweight, and resistant to corrosion.

Last verified on 17-03-2026

Explanation

• A change in physical appearance or state of a substance, such as a change in shape, size, color, or phase (solid, liquid, gas), is called a Physical Change.
  

The are examples of Physical Changes:

• Melting (ice cream, wax, chocolate, ice and change from solid to liquid)
• Phase changes (boiling, freezing, condensation)
• Crushing (chalk)
• Tearing (paper)
• Crumpling (aluminium foil)
• Stretching (rubber band)
• Mixing (sugar in water)
• Dissolving (sugar, salt in water)
• Moulding (clay, metals)
• Slicing (fruit)
• Forming of frost (from water vapors)
• Transition to a gas (change from liquid to gas)
• Change of durability (change in texture or strength)
• Changes to crystal form (change in crystal structure)

Last verified on 17-03-2026

Explanation

• A mature, large ovary and seed are characteristics of a fruit.
• A fruit is the mature ovary of a plant, which contains seeds.
• It typically surrounded by a fleshy, edible pulp.

Last verified on 17-03-2026