Scalar: A scalar is a quantity that has magnitude only.
Vector: A vector is a quantity that has magnitude and direction.
The moment (or torque) of a force: The turning effect of a force (or moment or torque) about a point is defined as the force x the perpendicular distance from the point to the line of action of the force, i.e. moment = F × d. UNIT: Nm.
The principle of moments: For a system to be in equilibrium, ∑ anticlockwise moments about a point = ∑ clockwise moments about the same point.
Centre of gravity: The centre of gravity is the single point within a body at which the entire weight of the body is considered to act.
Displacement: The displacement of a point B from a point A is the shortest distance from A to B, together with the direction. UNIT: m.
Mean Speed: Mean speed = total distance travelled total time taken x t ∆ = ∆ UNIT: ms-1.
Instantaneous Speed: instantaneous speed = rate of change of distance UNIT: ms-1.
Mean Velocity: Mean velocity = total displacement total time taken UNIT: ms-1.
Instantaneous Velocity: The velocity of a body is the rate of change of displacement. UNIT: ms-1
Mean Acceleration: Mean Acceleration = change in velocity time taken v t ∆ = ∆ UNIT: ms-2.
Instantaneous Acceleration: The instantaneous acceleration of a body is its rate of change of velocity. UNIT: ms
Terminal Velocity: The terminal velocity is the constant, maximum velocity of an object when the resistive forces on it are equal and opposite to the accelerating forces (e.g. pull of gravity).
Hookes Law: The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great.
Spring Constant: The spring constant is the force per unit extension. UNIT: Nm-1.
Stress: Stress is the force per unit cross-sectional area when equal opposing forces act on a body. UNIT: Pa or Nm-2.
Strain: Strain is defined as the extension per unit length due to an applied stress. UNIT: none
The Young Modulus: Young Modulus tensile stress tensile strain E = Unless otherwise indicated this is defined for the Hookes Law region. UNIT: Nm-2
Amplitude: The amplitude is defined as the maximum displacement of any particle from its equilibrium position.
Wavelength of a progressive wave: The wavelength of a progressive wave is the minimum distance between two points on the wave oscillating in phase.
Frequency of a wave: The frequency of a wave is the number of cycles of a wave that pass a given point in one second, or equivalently The frequency of a wave is the number of cycles of oscillation performed by any particle in the medium through which the wave is passing.
Velocity of a wave: The velocity of a wave is the distance that the wave profile moves per unit time.
Intensity of a wave: Energy per second passing normally through a given area / Area
A transverse wave: is one where the particle oscillations are at 90° (right angles) to the direction of travel (or propagation) of the wave.
Longitudinal wave: A longitudinal wave is one where the particle oscillations are in line with (parallel to) the direction of travel (or propagation) of the wave.
The principle of superposition: The principle of superposition states that if two or more waves occupy the same region then the total displacement at any one point is the vector sum of their individual displacements at that point.
Coherence: Waves or wave sources, which have a constant phase difference between them (and therefore must have the same frequency) are said to be coherent.
Phase difference: Phase difference is the difference in position of 2 points within a cycle of oscillation measured as a fraction of the cycle. [Alternatively it can be expressed as an angle where one whole cycle is 360°]
Snells law: At the boundary between any two given materials, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
Electric current, I: This is the rate of flow of electric charge. I = ∆Q/∆t. Unit: A
Potential difference (p.d.), V: The p.d. between two points is the energy converted from electrical potential energy to some other form per coulomb of charge flowing from one point to the other. Unit: volt (V) [= JC-1].
e.m.f: The e.m.f. of a source is the energy converted from some other form (e.g. chemical) to electrical potential energy per coulomb of charge flowing through the source. Unit: volt (V) [= JC-1].
Ohms Law: The current flowing through a metal wire at constant temperature is proportional to the p.d. across it.
Electrical Resistance, R: The resistance of a conductor is the p.d. (V) placed across it divided by the resulting current (I) through it. R = V / I Unit: ohm
Resistivity, ρ: The resistance, R, of a metal wire of length L and cross-sectional area A is given by R = ρ L / A, in which ρ , the resistivity, is a constant (at constant temperature) for the material of the wire. Unit: ohm-metre
Temperature coefficient of resistance, α: If the resistance of a conductor at 0C is R0 and its resistance at θ C is Rθ then α is defined by: α = (Rθ R0 ) / R0 θ . [It is the fractional change in resistance per degree rise in temperature above 0C.] Unit: °C-1
The Law of Conservation of Charge: Electric charge cannot be created or destroyed, (though positive and negative charges can neutralize each other). In a purely resistive circuit charge cannot pile up at a point.
Nucleon: Protons and neutrons have similar masses. They are both classed as nucleons.
Atomic mass number: A The atomic mass number of an atom is the number of nucleons (number of protons + number of neutrons) in its nucleus.
Atomic number, Z: The atomic number of an atom is the number of protons in its nucleus.This determines the chemical element which the atom represents.
Nuclide: A nuclide is a particular variety of nucleus, that is a nucleus with a particular A and Z.
Isotope: Isotopes are atoms with the same number of protons, but different numbers of neutrons in their nuclei.
Electron volt. (eV): This is the energy transferred when an electron moves between two points with a potential difference of 1 volt between them. 1 eV = 1.6 × 10-19 J
Ionisation: The removal of one or more electrons from an atom. 3.2.6(f)
Ionisation energy: The ionization energy of an atom is the minimum energy needed to remove an electron from the atom. Unit: J
Work function: The work function of a surface is the minimum energy needed to remove an electron from the surface. Unit: J [or eV]
Photoelectric effect: When light or ultraviolet radiation of short enough wavelength falls on a surface, electrons are emitted from the surface. This is the photoelectric effect.
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