ALevel物理必须要记住的核心定义！

All Definitions Needed For A2 Level Physics

Thermal Physics

The internal energy isa function of state and the total microscopic kinetic and potential energies ofthe particles composing the system.

The specific latent heat of fusion, Lf ,is defined as the amount of heat required per unit mass to change a substancefrom the solid phase to the liquid phase without any change in temperature

The specific latent heat of vaporization,Lv, is defined as the amount of heat required per unit mass tochange a substance from the liquid phase to the vapor phase without any changein temperature.

First law of thermodynamics state that internal energy is a function of state and theincrease in internal energy is equal to the sum of the heat supplied to systemand work done on system.

Circular Motion

Angular displacement, θis the angle subtended at centre of a circle by an arc of equal length to theradius.

Angular velocity, ω is the rate of change of angular displacement with respect totime.

The period T of an object in circularmotion is the time taken for the object to make one complete revolution.

The frequency f of an object incircular motion is the number of complete revolutions made by the object perunit time.

Oscillations

Periodic motion isthe regular, repetitive motion of a body which continually retraces its path atregular intervals.

Period Tof a periodic motion is the time to make one complete cycle.

Frequency fof a periodic motion is the number of cycles per unit time.

Angular frequency of a periodic motion is the rate of change of angulardisplacement with respect to time.

Displacement of an object is the distance of the oscillating particlefrom its equilibrium position at any instant.

Amplitude ofa periodic motion is the magnitude of the maximum displacement of theoscillating particle from the equilibrium position.

Simple Harmonic Motion (SHM) is defined as the oscillatory motion of a particlewhose acceleration a is always directed towards a fixed point and is directlyproportional to its displacement x from that fixed point but in the oppositedirection to the displacement.

Damping isthe process whereby energy is taken from the oscillating system.

Natural frequency of the system is the frequency at which it will vibratefreely.

Gravitation

Newton’s Law Of Universal Gravitation statesthat every particle in the Universe attracts every other particle with a forcethat is directly proportional to the product of their masses and inverselyproportional to the square of the distance between them.

Gravitational field strength at a point is defined as the gravitational force per unitmass acting on a mass placed at that point.

Gravitational potential energy, U of a point mass m, in a gravitational field, is the work doneby an external force in bringing that point mass from infinity to that point.

Gravitational potential at a point in a gravitational field is the work done perunit mass, by an external force, in bringing the mass from infinity to thatpoint.

Escape speed is the minimum speed with which a mass should be projectedfrom the Earth’s surface in order to escape Earth’s gravitation field.

Electric Field

The coulomb’s law states that theelectrostatic force between two point charges is proportional to the product oftheir charges and inversely inversely proportional to the square of thedistance between them.

The Electric field strength at apoint in an electric field is the electrostatic force per unit chargeexperienced by a small positive test charge placed at that point.

Electric Potential at a point in an electric field is the work done per unitcharge by an external agent in bringing a positive test charge from infinity tothat particular point without acceleration.

Electric potential energy of a charge in an electric field is defined as the work doneby an external force in bringing the charge from infinity to that point adistance r away.

The electron volt is defined asenergy that an electron (or proton) gains (or loses) when it is accelerated(ordecelerated) through a potential difference of 1 volt.

Electromagnetism

Magnetic flux density (B)is defined as the force acting per unit current per unit length on a wireplaced at right angles to the magnetic field.

1 Tesla isdefined as the magnetic flux density of a uniform magnetic field when a wire oflength 1m , carrying a current of 1A, placed perpendicular to the field,experiences a force of 1N in a direction at right angles to both the field andthe current.

ElectromagneticInduction

Magnetic flux through a plane surface isthe product of the magnetic flux density normal to the surface BN and the areaA of the surface.

The weber is defined as the magneticflux through a surface if a magnetic field of flux density 1 T existsperpendicularly to an area of 1 m2.

Magnetic Flux Linkage is defined as the product of the number of turns N of thecoil and the magnetic flux linking each turn.

Faraday’s Law states that the induced e.m.f. is directly proportional tothe rate of change of magnetic flux linkage or rate of cutting of magnetic fluxlinkage.

Lenz’s Law states that the induced e.m.f. will be directed such thatthe current which it causes to flow opposes the change that is producing it.

Alternating Current

The root-mean-square (r.m.s.) value of an alternatingcurrent is equivalent to the steady direct current thatconverts electrical energy to other forms of energy at the same average rate asthe alternating current in a given resistance.

Rectification is the process in which an alternating current is forced toonly flow in one direction.

Nuclear Physics

The mass defect of a nucleus isdefined as the difference between the mass of the separated nucleons and thecombined mass of the nucleus.

Nuclear fission is the disintegration of a heavy nucleus into two lighternuclei of approximately equal masses.

Nuclear fusion is the combining of the two light nuclei to produce aheavier nucleus.

Radioactive decay is the spontaneous disintegration of the nucleus of an atomwhich results in the emission of particles.

Background radiation refers to ionizing radiation emitted from a variety ofnatural and artificial radiation sources.

The activity of a radioactivesubstance is defined as the average number of atoms disintegrating per unittime.

The decay constant λ of a nucleus isdefined as its probability of decay per unit time.

Half-life isdefined as the time taken for half the original number of radioactive nuclei todecay.

Good luck with your A-Level!