Filtrate

(n.) A liquid obtained through filtration. This liquid consists of extremely small molecules or ions that pass through the holes in the filter paper.

Filtration

(n.) A method for separating a solid from a liquid by passing it through filter paper or a porous material.

Focal Length

(n.) The distance denoted as f that characterizes a converging lens: it is the distance between the center of the lens and its focal point.

Focus of a Converging Lens

(n.) A point denoted as F on the optical axis of the lens where light rays from rays parallel to the optical axis converge.

Fog

(n.m.) Mass of very small water droplets suspended in the air. Fog forms near the ground. When droplet condensation is at its maximum, there is an aqueous fog called mist. When it is at its minimum, there is only haze. The phenomenon of smog occurs when fog contains small solid particles.

Free Surface

(n.) A surface that is in contact with the air.

Freezing Point

(n.) Temperature at which a substance begins to solidify when cooled. The freezing point of pure water is 0°C.

Frequency

(n.) The number of elementary patterns of a periodic quantity per second. It is denoted by f or N and is expressed in hertz, symbol Hz.

Fuel

(n.) Substance that, in the presence of an oxidizing agent, can burn and thus undergo combustion.

Fusion

(n.) The transition from a solid state to a liquid state.