| Glossary | ||||||||||||||
| theory
— well-verified set of explanations that typically are supported by a large body of scientific evidence. Theories generally start as hypotheses. A hypothesis is elevated to the status of a theory when it becomes supported by a large enough body of evidence. thermal conductivity — measure of a material’s ability to conduct heat. Thermal conductivity has units of watts per meter per degree Celsius (W m−1 ºC−1). A thermal conductivity of 1 W/(m ºC) means one watt of heat flows through a one meter cube when the temperature difference is 1ºC. thermal energy — kinetic energy that comes from the random motion of atoms and/or molecules due to the effects of temperature. thermal equilibrium — condition of equal temperature at which no heat flows. thermodynamics — study of heat and its transformation to and from mechanical energy. thermometer — instrument that measures or senses temperature. third law of thermodynamics — absolute zero is the minimum possible temperature at which the entropy of a system is zero. The implication of the third law is that there exists no temperature below absolute zero. threshold frequency — minimum frequency of light for a given metal that causes electrons to be ejected through the photoelectric effect. Related to the work function of the metal. torque — product of force and the perpendicular distance between its point of application and the center of rotation. Units of torque are newton meters (N m). total internal reflection — complete reflection of an incident light ray back into the incident media. This occurs at a boundary with a material that has a lower index of refraction. Total internal reflection occurs at angles of incidence greater than a critical angle that depends on the difference in refractive indices. trajectory — path a projectile follows. In two dimensions, the trajectory is a curved path due to a constant horizontal velocity and an accelerating vertical velocity. | transformer
— device that increases or decreases voltage in AC circuits in order to minimize energy lost during transmission. translation — linear motion that results in a change in location. Other types of motion include rotation and oscillation. translucent — optical device that allows only some light to pass through it. The light may change direction many times as it passes through a translucent material, creating a distorted image. transparent — optical device that allows all the light to pass through it without distorting the image. transverse — direction perpendicular to the long direction or direction of motion. Transverse wave: type of wave in which the oscillations are perpendicular to the wave’s direction of motion. trough — minimum value or lowest amplitude of a wave. ultraviolet light — form of electromagnetic radiation at somewhat higher frequencies than visible light. uncertainty principle — momentum and position of a quantum particle cannot be known simultaneously better than ΔhΔp = h/4π, nor is possible to know energy and time simultaneously better than ΔEΔt = h/4π. vacuum — void or absence of matter. variable — quantity that may take on different values. All possible values of a particular variable have the same dimensions. For example, speed is a variable that can have many different values, but each value has units of length over time and expresses the rate of change in position. vector — quantity that includes both magnitude (or value) and direction. Force, displacement, and velocity are vectors. vector diagram — graphical representation of a vector in which the coordinate axes are scaled to represent the components of the vector in perpendicular directions. | |||||||||||||
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