Definitions for Physics Electrons, Waves and Quantum

admin / January 16, 2018
Question Answer
Explain Electric Current (Vector) A net flow of charged particles. In a metal it is due to a net drift of conduction electrons, while in an electrolyte it is due to a flow of ions. In a vacuum a beam of electrons or other charged particles can constitute a current. Conventional : + to –
Define The Coulomb the amount of charge supplied when a current of 1 ampere passes for 1 second. Charge is defined as the product of current and time.
State what is meant by mean drift velocity The result of the gradual migration of conduction electrons though a material under the action of an applied potential difference.It is much slower than the speeds associated with their random thermal motion. Average rate of change of disp of the con elec
Describe Kirchhoff's first law The sum of the currents entering any junction (or point) in a circuit is equal to the sum of the currents leaving that junction (or point). Conservation of charge.
Define Potential Difference The electrical energy transferred per unit charge when electrical energy is converted into another form of energy.
Define Electromotive Force The electrical energy transferred per unit charge when another form of energy is converted into electrical energy.
Define The Volt 1 joule per coulomb
Explain the meaning of the term terminal p.d. The potential difference across the terminals of an electrical supply when 'under load'
Define Resistance The ratio of the potential difference across a component to the current through it. Expressed by R = V/I.
State Ohm's Law The current through a conductor is proportional to the potential difference across it providing physical conditions such as temperature remain constant.
Define The Ohm 1 volt per ampere
Define Resistivity Resistivity is defined by the equation relating the resistance of a conductor to its physical dimensions of length and cross sectional area. It is a property of the material. R= (pl)/A.
State Kirchhoff's Second Law round any closed loop in a circuit the sum of the electromotive forces is equal to the sum of potential differences. Conservation of energy.
Define The Kilowatt Hour A unit of energy and is the energy delivered by a supply of 1 kilowatt running for 1 hour.
Describe and distinguish between longitudinal and transverse waves. Transverse: The direction of oscillation is perpendicular to the direction of wave travel, or at right angles to the direction of propagation. Longitudinal: Direction of the oscillations is in the direction of travel.
Define the term Displacement The distance moved by any part of the medium (or of the wave) from its rest position. Can be positive or negative.
Define the term Amplitude the maximum displacement, for example the maximum distance moved by any part of the medium from the rest position. Always Positive.
Define the term Wavelength The smallest distance between two points that have the same pattern of oscillation, for example are moving in phase with each other. It is also the distance the wave travels before the pattern of behaviour repeats itself.
Define the term Period The time taken for one complete (pattern of) oscillation to take place at any given point.
Define the term phase difference A measure of the delay between the pattern of oscillation at one point and the pattern of oscillation at another. Given in radians.
Define the term Frequency The number of oscillations per unit time at a given point. Expressed in Hz
Define the term Speed of a wave The distance travelled by the wave per unit time. Given by v = f?
State the principle of superposition States that, when two or more waves of the same type exist at the same time in the same place, the resultant is found by adding the displacements due to the individual waves.
Explain the term Interference The process by which two wave systems combining can produce either reinforcement (constructive) or cancellation (destructive). This can be partial or total. The result at any point in space and time is governed by the principle of superposition.
Explain the term coherence Wave sources are said to be coherent if they have a constant phase difference. The phase difference does not have to be zero. Althought it is a possibility.
Explain the term phase difference and path difference Waves from two different sources have a phase difference at a given point that depends upon the distances travelled by the progressive wave systems from their individual sources. expresses the extent to which they are out of step in terms of phase angle.
Explain what is meant by a stationary or standing wave A stationary or standing wave is formed when two progressive waves of the same frequency travel in opposite directions through the same medium. Unlike a progressive wave there is no net transfer of energy, there is often a considerable energy storage.
Define the term node In a Stationary wave, points where the displacement of the medium is always zero are called nodes.
Define the term antinode Points where the displacement is a maximum (positive and negative) in a stationary wave.
Define the term fundamental mode of vibration The oscillation pattern at the lowest frequency for which for which a stationary wave can exist.
Define the term Harmonic any frequency of vibration, above and including the frequency corresponding to the fundamental mode, for which a standing or stationary wave can be set up.
Define the electron volt Is a Unit of energy and is the energy gained (or lost) by an electron moving through a potential difference of 1V.
Define the term work function The minimum energy required to release an electron from the metal.
Define the threshold Frequency The minimum frequency of radiation that can cause photo-emission of electrons from a particular metal surface.

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