PPSC Everyday Science MCQs

Metal structures expand in hot weather.
Gaps prevent buckling and structural damage.

Melting occurs when a solid gains enough energy to become liquid.
It happens at the melting point under fixed pressure.

Freezing removes energy from a liquid until it forms a solid.
For pure water at standard pressure, this occurs at 0°C.

Evaporation occurs at the surface of a liquid.
Higher temperature and moving air usually increase its rate.

Condensation occurs when gas particles lose energy.
Water vapor condenses into droplets on a cool surface.

The highest-energy water molecules escape during evaporation.
This lowers the average energy and temperature of the skin.

Wind carries away water vapor near the fabric.
This maintains a concentration difference and speeds evaporation.

At boiling, vapor bubbles form throughout the liquid.
It occurs when vapor pressure matches external pressure.

Atmospheric pressure decreases with altitude.
Lower pressure allows water to boil at a lower temperature.

Boiling water is cooler at high altitude.
The lower cooking temperature slows many cooking processes.

Pressure inside the cooker increases above atmospheric pressure.
Water then boils at a higher temperature and cooks food faster.

Visible light is part of the electromagnetic spectrum.
It can travel through a vacuum.