Teaching Science Glossary



radiant energy: Energy associated with electromagnetic radiation. An object that absorbs radiant energy increases in temperature. Radiant energy is given off substances that are heated.
radiation: In terms of heating and cooling, radiation represents the emission of electromagnetic radiation from one object that is absorbed by another object. The object that has absorbed the electromagnetic radiation or radiant heat will increase in internal energy.
radio telescope: A telescope that detects radio waves.
rarefaction: A region of a material of lower than average pressure. The particles in this part of the material are more separated than in other parts.
ray: An arrow used in diagrams to show the direction of light travel. Ray diagrams are diagrams that explain light phenomena.
reaction force: A force that is created in response to the application of an action force.
real image: An image formed by a curved mirror or lens where the light actually passes through it. A real image can be seen on a screen. The images formed at the retinas of our eyes are real images.
red giant: A stage in the life of a star.
redox reaction: A reaction that involves both oxidation and reduction.
reductant: A substance that causes another substance to undergo a reduction reaction; a reductant donates one or more electrons to the substance it reduces.
reduction: Part of a redox reaction where a substance accepts electrons from an oxidant.
refraction: A phenomenon where light changes speed in passing from one transparent material into another.
relative atomic mass: The weighted mean of the relative isotopes relative to the mass of the carbon 12 isotope, taken as 12 units.
relative humidity: The ratio of the amount of actual water vapour in the air, for a given volume, to the amount of water required to saturate the air.
residual current device (RCD): A device used in AC circuits that compares the current flowing in the active wire with the current flowing in the neutral wire. Any disparity in current will cause the RCD to induce an open circuit.
resistance: As the term suggests, this is a quantity that gives the strength of opposition to current. An object that has high resistance will only let a small current through it. All loads have a certain amount of resistance. Conductors have a lower resistance than insulators. Resistance is measured in ohms.
resistor: A conductor used in electric circuits with a known resistance.
resonance: A phenomenon where some sound frequencies are amplified. Resonance occurs in resonating cavities or resonating chambers.
resonant frequencies: The frequencies that cause resonance to occur.
resonating cavity or chamber: A region where sound waves reflect causing amplified waves. These amplified waves correspond to certain frequencies called ‘resonant frequencies’.
retina: The back of the eye where real images are formed.
retrograde motion: The apparent motion of a moon or planet opposite to the dominant direction of the orbiting and rotating of the Sun and planets.
reverse reaction: This is where, in an equilibrium reaction, bonds are reformed to produce the reactant compounds.
rheopectic fluid: A non-Newtonian fluid. Rheopectic liquids increase in viscosity under a constantly applied force and are sometimes called ‘stir-thickening liquids’.
Richter Magnitude Scale: A scale that measures the total amount of energy released in an earthquake.
rock: A consolidated aggregate of minerals or particles of other rocks; although there are exceptions to this definition, coal and natural glass are also considered rocks.
rock cycle: A process of rock recycling.
rolling friction: Friction force that tends to slow a wheel rolling along a surface.

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