PPSC MCQs

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.

Ice has an open crystal structure that occupies more volume.
Its lower density causes it to float on water.

Wood and many plastics conduct heat poorly.
They reduce heat transfer to the user's hand.

Freezing expands water into a less dense solid structure.
The resulting ice is buoyant in liquid water.