| Glossary | ||||||||||||||
| emissivity
— relative ability of a surface to emit thermal energy by radiation.
The emissivity is the ratio of the actual power emitted as thermal radiation divided by the power emitted by a perfect blackbody at the same temperature. The value of emissivity ε is between zero (no power radiated) and one (radiates as a perfect blackbody), or 0 ≤ ε ≤ 1. energy — quantity that causes matter to change and mediates how much change occurs. energy levels — set of quantum states for the electron energies in an atom. The electron must absorb or release energy to change from one level to another. engineering — creative application of science to design technologies that solve problems or meet needs. entropy — thermodynamic quantity calculated by dividing heat by temperature. The entropy of a system measures the thermal energy per degree that is not available for converting to output work. equilibrium — state of a system in which all forces are in balance. There is zero net force on a system in equilibrium. equipotential — two or more positions in an electric field that have the same electric potential. In an electric field diagram, equipotential lines are lines of constant electric potential. equivalent resistance — total or combined resistance of a circuit with more than one resistor. Also called the effective resistance. escape velocity — minimum initial velocity needed to completely break away from a gravitational field. Objects with less than the escape velocity eventually fall back towards the parent body. Objects with greater than the escape velocity may never come back if launched on the right trajectory. excited state — energy level of an atom that has higher energy than the ground state. An electron will move from the ground state to an excited state by absorbing energy from light; if it returns to the ground state it will emit light. experiment — controlled situation set up specifically to observe what happens under a well-defined set of circumstances. | exponent
— value of b in an expression ab. Fahrenheit scale — relative temperature scale where 32°F is defined as the temperature that water freezes and 212°F is the temperature that water boils. Faraday’s law of induction — changing magnetic flux through a coil of wire will induce an emf in the wire that is proportional to the number of loops and the rate of change of the magnetic field. ferromagnetic — a type of substance, such as iron, that experiences strong magnetic forces when in the presence of a magnet. Iron, nickel, and cobalt are ferromagnetic materials. first law of thermodynamics — change in energy of a system is the heat added to the system plus the work done on the system. Referred to as the conservation of energy for thermodynamics. fission — nuclear reaction in which a nucleus is split, thereby releasing large amounts of energy. fluid — substance that can change shape and flow readily in response to any applied forces, such as a liquid or a gas. focal length — distance from the center of an optical device to the focal point. focal point — point at which light rays that are parallel to the optical axis of an optical device either meet (converge) or diverge after being reflected or refracted. force — action on a body that causes change in motion. Measured in newtons (N). force field — field that exerts a force on objects in it. Examples include magnetic, electric, and gravitational fields. Fourier’s theorem — any repetitive signal, such as a multi-frequency wave, can be replaced by a series of single-frequency sine waves of different amplitudes and phases. free fall — motion of an object when the only force acting on it is the force of gravity. free-body diagram — sketch that isolates a single object and uses arrows to represent the strength, location, and direction of all forces acting on the object. | |||||||||||||
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