| Glossary | ||||||||||||||
| origin
— point in space where the position = 0 m in one dimension or (0,0,0) m in three dimensions. The origin is the fixed reference point for position data and is the location where all the coordinate axes intersect. oscillator — system that exhibits harmonic motion. output arm — distance on a lever between the location from which the output force is applied and the fulcrum. output force — force produced by a machine. parallel circuit — electric circuit where the electric current can take more than one path. Pauli exclusion principle — quantum rule that no two electrons (or fermions) may occupy the same quantum state in the same system. period — time it takes to complete one full cycle of an oscillation. Equal to the inverse of the frequency of oscillation. periodic force — force whose magnitude or direction has a repetitive or cyclic pattern. permanent magnet — magnetic object that retains its magnetism even when it is not in an external magnetic field. permeability of free space — physical constant describing how effectively a magnetic field can be established in a vacuum. Also called the vacuum permeability. The permeability of free space is used in the equation for the magnetic field surrounding a current-carrying wire. phase — Waves: location of a wave with respect to its complete cycle. Usually given in degrees, where 360 degrees is one full cycle. A phase of 180 degrees is a half cycle. Matter: state of solid, liquid, gas, or plasma. phases of matter — matter can exist in only four different states: gas, liquid, solid, and plasma. The first three are regularly encountered as part of everyday life. phosphorescence — type of light emission by a material where there is a delay between the absorption and re-emission of the light. The delay is caused by the electrons being excited to higher energy levels that do not decay rapidly back to lower energy levels. | photoelectric effect
— ejection of electrons from a metal when light of certain frequencies is incident upon it. photon — smallest, discrete packet of electromagnetic energy that makes up light in the quantum theory. photovoltaic cell — device that converts energy from the Sun’s light into electricity. pitch — perceived frequency of sound. High pitch is high frequency and low pitch is low frequency. pixel — smallest element of an electronic image, such as the picture from a digital camera. Planck’s constant — fundamental constant that determines the scale of quantum phenomena. Planck’s constant corresponds to the ratio of the energy of light to its frequency. The value of Planck’s constant is h = 6.63×10−34 J s. polar coordinates — coordinates that use radius (or magnitude) and angle to define points in space. polarity — condition of a system that describes opposing physical characteristics. Examples include the poles of a magnet and electrical charges. polarization — property of a transverse wave that describes the direction of the oscillation in a plane perpendicular to the wave’s direction of motion. position — vector quantity that locates a unique point in space relative to an origin. positron — particle that has the same mass as an electron and electric charge of +1.6×10-19 C. potential difference — difference in the electric potential between two locations. In electric circuits, potential difference and voltage are often used interchangeably. potential energy — energy of position—often due to gravity, but also includes other forms such as elastic potential energy and pressure. Measured in joules (J). pound (lb) — English unit of force equal to 4.448 N. The force due to the Earth’s gravity is often expressed in pounds. | |||||||||||||
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