Physics Definitions and Concepts

8/10/2019 Physics Definitions and Concepts

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Physics Definitions and Concepts

Chapter 1: Introduction To Physics

Physicalquantities

QUANTITIES that can be measured.

Base quantities PHYSICAL QUANTITIES that cannot be defined in terms of other physicalquantities but has its own definition.

(length, time, mass, electric current, temperature)

Derivedquantities

PHYSICAL QUANTITIES that are derived from base quantities bymultiplication or division or both.

Scalar quantity QUANTITY which has magnitude only.

Vector quantity QUANTITY which has both magnitudeand direction.

Consistency ABILITY to register the same reading when a measurement is repeated.

Accuracy DEGREE of closeness of the measurements to the actual value.

Sensitivity ABILITY to detect a small change in the value of measurement.

Error DIFFERENCE between actual value of quantity and the value obtained inmeasurement.

Zero error ERROR that arises when the measuring instrument does not start from exactlyzero.

Systematicerrors

CUMULATIVE ERRORS that can be corrected, if the errors are known.

(zero error, incorrect calibration of measuring instrument)

Random errors ERRORS that arise from unknown and unpredictable variations in condition,and will produce a different error every time.

(human limitations, lack of sensitivity, natural errors, wrong technique)

Distance The TOTAL PATH travelled by an object from one point to the other.

Displacement The shortest distancebetween two points in a specific direction.

Speed The RATE of change of distance.

Velocity The RATE of change of displacement.

Acceleration The RATE of change of velocity.

Inertia PROPERTY of matter that causes it to resist any change in its motion or

state of rest.

Mass QUANTITY of matter in the object.

Momentum PRODUCT of mass and velocity.

Elastic collision The collision where the kinetic energy is conservedafter the collision.

Inelastic collision The collision where the kinetic energy is not conservedafter thecollision

Force Pulling or a pushing ACTION on an object.

Frictional force FORCE that opposing motion.

Impulse The change in momentum.

Chapter 2 Forces and Motion


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Impulsive force RATE of change of momentum.

Force of Gravity/Gravitational force

FORCE originated from centre of Earth that pulls objects towards theground.

Free fall FALLING of object with acceleration due to gravity only.

Weight The gravitational forceacting on the object.

Resultant force SINGLE FORCE which combines two or more forces which act on anobject.

Force in equilibrium/Balanced forces

Forces act upon an object causes it remain stationary or moves withconstant velocity.// Resultant force acting on object is ZERO.

Work The PRODUCT of applied force acting on object and displacement in thedirection of force.

Energy ABILITY to do work.

Kinetic energy ENERGY possessed by a movingobject.

Gravitationalpotential energy

ENERGY STORED in the object because of its heightabove the earthsurface.

Elastic potentialenergy

ENERGY STORED in the object(spring) because of stretching orcompressing it.

Power RATE of energy transferred./Amount of work done per second.

Elasticity PROPERTY of an object that enables it to return to its original shape ordimensions after applied force is removed.

Spring constant FORCE needed to extend a spring per unit length.

Elastic limit MAXIMUM STRETCHING FORCE which can be applied to an elasticmaterial before it ceases to be elastic.

PRINCIPLE & LAW

Principle of

conservation ofmomentum

The total momentumin a closed system alwaysremains constant;

that is, total momentum before collision will equal to the total momentumafter collision.

Principle ofconservation ofenergy

Energy CANNOT be created or destroyed, but it can be transformed fromone kind to another, and the total energy remains constant.

Newtons first law ofmotion

A body will either remain at rest or continue with constant velocity unlessit is acted by an external force.

Newtons second lawof motion

The rate of change of momentumof a body is directly proportionaltotheresultant force acting on the body and is in the same direction.

Newtons third law ofmotion

To every ACTION, there is areactionwith the same magnitude but in theopposite direction.

Hookes law The extension of a springis directly proportionalto the applied forceprovided the elastic limit is not exceeded.


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CHAPTER 3 FORCES AND PRESSURE

Pressure FORCE acting normally on a unit surface area.

Density Mass per unit volume

Gas pressure Force per unit area exerted by the gas particlesas they collide with the

walls of the container.

Atmospheric pressure The force per unit area exerted against a surface by the weight of theair moleculesabove that surface.

Buoyant force/Upthrust

Upward force acting on an object which is immersed in a fluid.

PRINCIPLE & LAW

Law of Floatation The weight of an object floating on the surface of a liquid is equal to theweight of water displaced by the object.

Pascals Principle PRESSURE applied to an enclosed fluid is transmitted uniformly in alldirections throughout the fluid.

Archimedes Principle The buoyant force on a body immersed in a fluid is equal to the weightof the fluid displaced by that object.

Bernoullis Principle The pressure of a moving fluid decreases as the speed of the fluidincreases, and vice versa.

CHAPTER 4 HEAT

Temperature DEGREE of hotnessof an object./Amount of kinetic energy in anobject.

Heat A form of energytransferred from hot to cold object.

Thermal equilibrium A STATE where objects in thermal contact reach the same

temperatureand the net of heat flowbetween the objects arezero.

Heat capacity Amount of heat energy required to raise the temperature of a materialby 1

0C.

Specific heat capacity Amount of heat energy required to raise the temperature of 1 kgmaterial by 1 0C.

Latent heat Heat absorbed or released when a substance changes its state withouta change in temperature.

Specific latent heat offusion

Amount of heat required to melt 1 kg of a solid at its melting pointwithout a change in temperature.

Specific latent heat ofvaporisation

Amount of heat required to change 1 kg of a liquid at its boiling point togas without a change in temperature.

LAW

Boyles Law The pressure of a fixed mass of gas is inversely proportional to itsvolume, provided the temperature of gas is constant.

Charles Law The volume of a fixed mass of gas is directly proportional to its absolutetemperature, provided the pressure of gas is constant.

Pressure Law The pressure of a fixed mass of gas is directly proportional to itsabsolute temperature, provided the volume of gas is constant.


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CHAPTER 5 LIGHT

Real image Image that can be projected onto a screen.

Virtual image Image that CANNOT be projected onto a screen.

Focal point(mirror) The POINT to which all rays parallel to principal axis converge or from

which they appear to diverge.

Focal length(mirror) The DISTANCE between the focal point and the pole of mirror.

Refraction The bending or change of direction of lightdue to a change in speedas it enters a medium of different optical density.

Refractive index The refractive index, of a material is given by:

v

c , where c is speed of light in vacuum, v is speed of light in the

medium.

Total internalreflection

Total reflection of a beam of light at the boundary of two mediums, whenthe angle of incidence in the denser medium exceeds a specific critical

angle.#Two conditions for total internal reflection to occur:

1. Light ray must travel from optically denser medium to less densemedium.

2. The angle of incidence must greater than critical angle.

Critical angle The ANGLE OF INCIDENCE which produces an angle of refraction of90

oas light travels from denser medium to less dense medium.

Focal point(lens) The POINT to which all rays parallel to the principle axis converge/diverge after refraction by the lens

Focal length(lens) The DISTANCE between focal point and optical centre of lens.

Linear magnification RATIO of the image distance, v to the object distance, u.

Power of lens

fPower

1 , where f is focal length(measured in meter).

PRINCIPLE & LAW

Law of Reflection The angle of incidence is equal to the angle of reflection (i = r), and theincident ray, normal and reflected ray lie in the same plane.

Snells Law For light passing from air into a medium of refractive index, :

r

i

sin

sin(a constant)

where iis the angle of incidence andr is the angle of refraction.

Lens formula

fvu

111 , uis object distance, vis image distance, fis focal length

CHAPTER 6 WAVES

Waves PROCESS of transferring energyfrom one location to another producedby an oscillating or vibrating motion.


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Wavefront An imaginary LINE that join all the points on the crest of a wave.

Transverse wave WAVE in which the vibration of particles in a medium is perpendiculartothe direction of propagation of the wave.

(water waves, light waves, microwaves)

Longitudinal wave WAVE in which the vibration of particles in a medium is parallel to the

direction of propagation of the wave.(sound waves, ultrasound)

Amplitude, a MAXIMUM DISPLACEMENT from its equilibrium position.

Period, T TIME TAKEN to complete one oscillation.

Frequency, f NUMBER of COMPLETE OSCILATION made in one second.

[SI unit = Hertz(Hz)/s-1

]

Wavelength, HORIZONTAL DISTANCE between two successivecrests or troughs.

Wave speed, v MEASUREMENT of how fast a crest is moving from its fixed point.

Wave speed, v=f wherefis frequency and is wavelength

Damping Occurred when an oscillating system loses energy to the surrounding

results the DECREASE in amplitude.

Resonance Occurs when a system is made to oscillate at a frequency equivalent to itsnatural frequencyby external force.

Natural frequency The frequency of a system which oscillates freely without external force.

Reflection of waves PHENOMENON where the return of all or part of the waves when theystrikes on an obstacle.

[direction ; v=; =; f =]

Refraction of waves PHENOMENON where there is a change of direction in waves motionwhen waves travel from one medium to another due to change in speed.

[direction ; v ; , f=]

Diffraction of waves PHENOMENON in which waves spread out as they passed through a gapor an obstacle.

[direction ; v =; =; f=]

Interference ofwaves

PHENOMENON where SUPERPOSITION of two waves originating fromtwo coherent sources.

Coherent source Waves that have same wavelength, frequencyand constant phasedifference.

Constructiveinterference

Occurs when crests or troughs of both waves coincide to produce a wavewith crests and troughs of maximum amplitude.

Destructiveinterference

Occurs when the crest of one wave coincides with the trough of the otherwave, thus canceling each other with the result that the resultant

amplitude is zero.

Antinode POINT where constructive interferenceoccurs.

Node POINT where destructive interferenceoccurs.

Monochromatic light LIGHT which has one color and one wavelength.

Electromagneticwaves

Propagating waves in space with electric and magnetic component.These components oscillate at right angle to each other and to thedirection of propagation of wave.


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PRINCIPLE

Principle ofsuperposition

When two waves overlap, the resultant displacementis equal to thesum of the displacement of the individual wave.

CHAPTER 7 ELECTRICITY

Electric current, I Therateof flow of electric charge.

[Unit: Ampere(A)/Cs-1

]

Electric field A regionin which an electric charge experiences an electric force.

Potential difference,V

WORK DONE in moving one coulomb of charge from one point toanother in an electric field.

[Unit: Volt(V)/JC-1

]

Ohmic conductor Conductors that obey Ohms Law.

Non-ohmicconductor

Conductors that do not obey Ohms Law.

Resistance, R RATIO of thepotential difference across the conductor to the currentflowing through it.

[Unit: Ohm()/VA-1

]

Superconductor A MATERIAL whose resistance becomes zero when its temperaturedrops to a certain value called critical temperature.

Electromotive force(e.m.f.)

Work done by a SOURCE in driving one coulomb of charge around acomplete circuit.

[Unit: Volt(V)]

Internal resistance, r The resistance against the moving charge due to the electrolyte in thesource.

Electrical energy ABILITY of the electric current to do work.Electric power, P The rate of electrical energy dissipatedor transferred.

[SI unit: Watt(W)/Js-1]

Power rating An electric kettle which is marked240 V 1500 W means that:

The electric kettle will consume 1500 J of electrical energy every onesecond if it is connected to the 240 V power supply.

LAW

Ohms Law The electric current flowing through a conductor is directlyproportionalto the potential difference across it if the temperature andother physical conditions are constant.

CHAPTER 8 ELECTROMAGNETISM

Electromagnet TEMPORARY MAGNET which acts as a magnet when the current isswitched on and loses its magnetism when current is switched off.

Magnetic field REGION in which a magnetic material experiences a force as the result ofa magnet or current-carrying conductor.


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Electromagneticinduction

PRODUCTION of an electromotive force(e.m.f.)/electric currentbychanging magnetic field.

Induced current CURRENT produced by changing of magnetic field.

Transformer ELECTRICAL DEVICE which increases or decreases an alternatingvoltage based on the principle of electromagnetic induction.

LAW

Lenzs Law The direction of the induced currentin a solenoid is such that itsmagnetic effect always opposesthe change producing it.

Faradays Law The magnitude of the induced electromotive force(e.m.f.) is directlyproportional to the rate in which the conductor cuts through the magneticfield lines.

RULE

Right Hand Grip Rule To determine the direction of the magnetic field of current-carryingconductor.

Flemings Left HandRule

To determine the direction of magnetic forceacting on the wire carryingcurrent.

Flemings RightHand Rule

To determine the direction of induced e.m.f. (and induced current).

CHAPTER 9 ELECTRONICS

Thermionic

emissionPROCESS of emission of electrons from heatedmetal surface.

Cathode ray Fastmoving ELECTRONS travel in a straight linein vacuum.

Cathode ray

oscilloscope(CRO)

INSTRUMENT that converts electronic and electrical signals to a visual

display.

Conductor MATERIAL which allows current to flow through them.

SemiconductorMATERIAL which has electrical conductivity between a conductor and an

insulator.

Insulator MATERIAL which does not conduct electric current.

DopingProcess of addingspecificimpuritiesto a pure semiconductor to increase

its conductivity.

Diode A DEVICE that allows current to flow in one directiononly.

Rectification Conversionof alternating current to direct current by diode.

Logic gates ELECTRONIC CIRCUIT with one or more inputs and one output.


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CHAPTER 10 RADIOACTIVITY

Atom An atom consists of a nucleus which is made up of protons and neutrons,with electrons orbiting the nucleus.

Proton number NUMBER of protonsin the nucleus of an atom.

Nucleon number NUMBER of protonsand neutronsin an atom.Isotopes Atoms of an element which have thesame proton numberbut different

nucleon number.

Radioactivity Thespontaneous and random decayofunstablenucleus into morestablenucleus with the emission of energetic particles or photons.

Radioactive decay PROCESS where unstable nucleus becomes a more stable nucleus byemitting radiations.

Alpha particles () Positively charged HELIUM nucleus, He2+.

Beta particles () Negatively charged fast moving ELECTRON.

Gamma rays ( ) Neutral electromagnetic wave.

Radioisotope Unstable isotopes which decay and give out radioactive emissions.

Half-life TIME TAKEN for the number of undecayed nuclei to reduce to half of itsoriginal number.

Atomic mass unit(a.m.u.) 1 atomic mass unitor 1 uis

12

1of the mass of the carbon-12 atom.

Nuclear fission Thesplittingof a heavy nucleus into two lighter nuclei with release largeamount of energy.

Nuclear fusion The combining of two lighter nuclei to form a heavier nucleus with releaselarge amount of energy.

PRINCIPLE

Einsteins Principleof Mass-EnergyConservation

The relationship between the mass and the energy is given by equation:

E = mc2

where E = energy released(J);

m= loss of mass or mass defect(kg);

c= speed of light = 3.00 108ms

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Physics Definitions and Concepts

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