D
De Broglie wavelength
A wavelength, given by = h/mv, which is associated with matter. Louis de Broglie proposed the idea that matter could be treated as waves in 1923 and applied this theory successfully to small particles like electrons.
A wavelength, given by = h/mv, which is associated with matter. Louis de Broglie proposed the idea that matter could be treated as waves in 1923 and applied this theory successfully to small particles like electrons.
Decay constant
A constant, , not to be confused with wavelength, that defines the speed at which a radioactive element undergoes decay. The greater is, the faster the element decays.
A constant, , not to be confused with wavelength, that defines the speed at which a radioactive element undergoes decay. The greater is, the faster the element decays.
Decibel
A logorithmic unit for measuring the volume of sound, which is the square of the amplitude of sound waves.
A logorithmic unit for measuring the volume of sound, which is the square of the amplitude of sound waves.
Deposition
The process by which a gas turns directly into a solid because it cannot exist as a liquid at certain pressures.
The process by which a gas turns directly into a solid because it cannot exist as a liquid at certain pressures.
Destructive interference
The cancellation of one wave by another wave that is exactly out of phase with the first. Despite the dramatic name of this phenomenon, nothing is “destroyed” by this interference—the two waves emerge intact once they have passed each other.
The cancellation of one wave by another wave that is exactly out of phase with the first. Despite the dramatic name of this phenomenon, nothing is “destroyed” by this interference—the two waves emerge intact once they have passed each other.
Diffraction
The bending of light at the corners of objects or as it passes through narrow slits or apertures.
The bending of light at the corners of objects or as it passes through narrow slits or apertures.
Diffraction grating
A sheet, film, or screen with a pattern of equally spaced slits. Typically the width of the slits and space between them is chosen to generate a particular diffraction pattern.
Direction
The property of a vector that distinguishes it from a scalar: while scalars have only a magnitude, vectors have both a magnitude and a direction. When graphing vectors in the xy-coordinate space, direction is usually given by the angle measured counterclockwise from the x-axis to the vector.
Directly proportional
Two quantities are directly proportional if an increase in one results in a proportional increase in the other, and a decrease in one results in a proportional decrease in the other. In a formula defining a certain quantity, those quantities to which it's directly proportional will appear in the numerator.
Dispersion
The separation of different color light via refraction.
Displacement
A vector quantity, commonly denoted by the vector s, which reflects an object’s change in spatial position. The displacement vector points from the object’s starting position to the object’s current position in space. If an object is moved from point A to point B in space along path AB, the magnitude of the object’s displacement is the separation of points A and B. Note that the path an object takes to get from point A to point B does not figure when deining displacement.
Distance
A scalar quantity. If an object is moved from point A to point B in space along pathAB, the distance that the object has traveled is the length of the path AB. Distance is to be contrasted with displacement, which is simply a measure of the distance between points A and B, and doesn’t take into account the path followed between Aand B.
Doppler shift
Waves produced by a source that is moving with respect to the observer will seem to have a higher frequency and smaller wavelength if the motion is towards the observer, and a lower frequency and longer wavelength if the motion is away from the observer. The speed of the waves is independent of the motion of the source.
Dot product
A form of vector multiplication, where two vectors are multiplied to produce a scalar. The dot product of two vectors, A and B, is expressed by the equation A · B =AB cos .
Dynamics
The application of kinematics to understand why objects move the way they do. More precisely, dynamics is the study of how forces cause motion.
E
Efficiency
For a heat engine, the ratio of work done by the engine to heat intake. Efficiency is never 100%.
For a heat engine, the ratio of work done by the engine to heat intake. Efficiency is never 100%.
Elastic collision
A collision in which both kinetic energy and momentum are conserved.
Electric generator
A device that converts mechanical energy to electrical energy by rotating a coil in a magnetic field; sometimes called a “dynamo.”
Electromagnetic induction
The property by which a charge moving in a magnetic field creates an electric field.
Electromagnetic spectrum
The spectrum containing all the different kinds of electromagnetic waves, ranging in wavelength and frequency.
Electromagnetic wave
A transverse traveling wave created by the oscillations of an electric field and a magnetic field. Electromagnetic waves travel at the speed of light, m/s. Examples include microwaves, X rays, and visible light.
Electron
A negatively charged particle that orbits the nucleus of the atom.
Electronvolt
A unit of measurement for energy on atomic levels. 1 eV = J.
Energy
A conserved scalar quantity associated with the state or condition of an object or system of objects. We can roughly define energy as the capacity for an object or system to do work. There are many different types of energy, such as kinetic energy, potential energy, thermal energy, chemical energy, mechanical energy, and electrical energy.
Entropy
The disorder of a system.
Equilibrium
The state of a nonrotating object upon whom the net torque acting is zero.
Equilibrium position
The stable position of a system where the net force acting on the object is zero.
F
- Faraday’s Law
- A law, || = , which states that the induced emf is the change in magnetic flux in a certain time.
- First Law of Thermodynamics
- Essentially a restatement of energy conservation, it states that the change in the internal energy of a system is equal to the heat added plus the work done on the system.
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Focal length
- The distance between the focal point and the vertex of a mirror or lens. For concave mirrors and convex lenses, this number is positive. For convex mirrors and concave lenses, this number is negative.
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Focal point
- The point of a mirror or lens where all light that runs parallel to the principal axis will be focused. Concave mirrors and convex lenses are designed to focus light into the focal point. Convex mirrors and concave lenses focus light away from the focal point.
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Force
- A push or a pull that causes an object to accelerate.
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Free-body diagram
- Illustrates the forces acting on an object, drawn as vectors originating from the center of the object.
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Frequency
- The number of cycles executed by a system in one second. Frequency is the inverse of period, f = 1/T. Frequency is measured in hertz, Hz.
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Frictional force
- A force caused by the roughness of two materials in contact, deformations in the materials, and a molecular attraction between the materials. Frictional forces are always parallel to the plane of contact between two surfaces and opposite the direction that the object is being pushed or pulled.
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Fundamental
- The standing wave with the lowest frequency that is supported by a string with both ends tied down is called the fundamental, or resonance, of the string. The wavelength of the fundamental is twice the length of the string, .