(Phys)Compiled Definitions and Principles for ASlevel paper 1/Paper 2

8/14/2019 (Phys)Compiled Definitions and Principles for ASlevel paper 1/Paper 2

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TERMINOLOGY AND PRINCIPLES

Measurements

Base Quantities- physical quantities that cannot be broken down any further

Derived Quantities- physical quantities that are obtained by combining the basequantities i.e. can be expressed as product or quotient of other

physical quantities.

Scalar quantities has magnitude only.

Vector Quantities has magnitude and direction.

Systematic Errors (AS) all readings have the same error Errors which will result the scattered equally about the true

value; Can be reduced (but never eliminated) by averaging Error is due to observer

Kinematics

Distance total length along a specified path

Displacement Distance moved from a fixed point in a specified direction.

Speed rate of change of distance

Velocity rate of change of displacement

Acceleration rate of change of velocity

Note: Projectile motionFor any projectile

Its VERTICAL motion is at constant ACCELERATION Its HORIZONTAL is at constant SPEED

Linear momentum - product of mass and velocity of an object and it acts in the samedirection as the velocity

Newtons Laws FIRST LAW An object will remain at rest or continue to move in a constant velocity unless

acted upon by an external resultant force.

SECOND LAW Rate of change of momentum of a body is directly proportional to the external

resultant force acting upon it and it occurs in the direction of the force.

Rate of momentum F


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(mv - mu) Ft

m(v - u) Ft

ma F

F= kma , k =1

F = ma

THIRD LAW If body A exerts a force on body B then body B exerts equal but opposite in

direction to force on body A

Force, Energy and Equilibrium

Mass Measure of Bodys reluctance to change in its state of motion (i.e. its inertia).(Constant and a scalar quantity)

Weight Gravitational force acting on the object.(A vector quantity)

Centre of Gravity Point of which the whole weight of the body acts upon.

Centre of Mass Point through which an applied force causes no rotation.

Principle of Conservation of Momentum The total momentum of a systemremains constant provided that no external forceacts upon the system (isolated system).

*Applies for both elastic and inelastic collision as well as explosion

Upthrust caused by the pressure that the fluid exerts on the object (on the top andthe bottom of an object)

It is due to the difference in fluid pressure between the top and the bottom ofthe object.

Acts vertically upwards (Archimedes Principle) Equal to the weight of the fluid displaced when a

body is wholly or partially immersed in a fluid.

For an object immersed in a fluid the buoyancy force is equal to the weight of thefluid displaced Can be applied generally of not just when the object has a regular shape.

An object floats in water because the buoyancyforce on it is equal and opposite in direction to its weight.

For a body to be in equilibrium Resultant force is zero in any direction (closed triangle) Resultant moment or torque is zero about any point. Stationary or move in a constant velocity


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Moment of the force is the product of the force and the perpendicular distance ofthe line of action of the force from the pivot.

Couple consists of two equal and opposite forces whose lines of actions do notcoincide.

Torque of a couple is the product of one of the forces and the perpendiculardistance between the forces.(No linear acceleration) -therefore producing a turning effect.

The Principle of Moments states that for a body to be in rotational equilibrium thesum of the clockwise moments about any point must be equalto the sum of anticlockwise moments about the same point.

Work product of force and the distance moved in the direction of force.

Energy stored ability to do work.

Kinetic energy is the stored ability to do work due to its motion.

Potential energy is the stored energy available to do work due to its position orshape.

Principle of conservation of energy Energy may be transferred from one form toanother but it cannot be created nor is destroyed i.e.total energy of an isolated system constant.

Power work done per unit time

Electric Fields

Electric field is a region of space where a charge experiences a force.

Direction of electromagnetic field is the direction in which a positive chargewould move if it were free to do so.

Shows the direction of force on the positive charge.Electric field strength Force per unit positive charge placed at a point.

The closer the magnetic field the stronger it is.

Electric Circuits

Electric current is the rate of flow of charged particles.

Conventional current flows from the positive terminal of the battery to thenegative terminal (form a high potential to a low potential) i.e. inthe direction of flow of positive charge.

Flow of electrons is from the negative terminal of the battery to the positiveterminal (form a low potential to a high potential) i.e. in the direction offlow of electrons.

Direct Current direction of current is fixed.


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Alternating current motion of electric charges is periodically reversed.

Potential Difference amount of electrical energy transferred to other forms ofenergy when unit charge passes between two points.

Electromotive force - amount of energy transferred from other forms of energy toelectrical energy by a source in driving unit charge around acomplete circuit.

Resistance ratio of potential difference across a component to the current in it.

Ohms Law current through a conductor is directly proportional to the potentialdifference across it provided that temperature is constant.

Resistivity is numerically the resistance of a sample unit length and the crosssectional area at a certain temperature.

Kirchoffs Laws FIRST LAW (CONSERVATION OF

CHARGE) Charge entering each second = Charge leaving each second

(I.e. charge cannot be created nor destroyed)

SECOND LAW (CONSERVATION OFENERGY)

In any closed circuit or loop the sum of electromotive force is equal to the sumof potential difference.

Radioactivity

Proton number isthe number of protons in the nucleus of the atom.

Nucleon number is the total numberof protons and neutrons in the nucleus of theatom.

Relative Atomic Mass ratio of mass of an atom to 1/12 mass of a C-12 atom (unitu)

Isotopes atoms with the same proton number but different nucleon number. Isotopes have the same chemical properties as they have the same number of

electrons but have slightly different mass.

Nuclide an atom of a particular nuclear structure.

Nuclear Reaction nucleus may be transmuted to a different nucleus bybombarding it with high energy particles.

Nuclear Radiation 3 types of radiation: -particles, -particles, -particles.

Note: Principle of Conservation of Charge and Nucleons -


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In radioactive decay (nuclear processes) the charge and the number of nucleons arethe same before and after decay.

Note: Principle of Conservation of Energy(Energy cannot be created nor destroyed)-mass and energy is equivalent (E=mc) in any nuclear processes.

Radioactive decay is theprocess by which unstable nuclei become more stable byemitting or particles or radiation.

Spontaneous decay rate of decay is unaffected by environmental changes e.g.temperature.

Random decay cannot predict which particular nucleus decay next Constant probability of decay per unit time of a nucleus.

Background Radiation consists of cosmic rays, particles emitted by radioactivecarbon in the atmosphere

E.g. radon gas, radiation from rocks and etc...

Background count Even in the absence of radioactive source, the GM tube willregister some counts it is caused by background radiation.

Fusion Light atoms fuses together to make heavier atoms which can only occur ifenergy is released.

(Source of energy from the Sun and stars)

Fission heavy atoms is broken into two roughly equal parts then energy is released. (Used in nuclear power station)

Mass defect is the difference between the mass and its constituents particlestaken separately and the mass of the atom itself.

Iron has the greatest mass defect thus it is the most abundant element. Theory: atom which has a high mass defect has a great deal of work to be done

on it in order to separate into its constituent nucleons (in a low energy state)

Binding energy is the work done to separate the atom into several individualprotons, electrons and neutrons.

Half life the average time it takes for half of the atoms of any nuclide to decay.

Nucleon - a proton and nucleon

The activity of a radioactive isotope is the number of disintegrations per second.

Phases of Matter

Density mass per unit volume

Brownian motion is the random movement of smoke particles.


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Observation smoke particles scatter the light shining on them and so tinyspecks of lights can be observed

Explanation irregular random movement of the smoke particles is due touneven bombardment of invisible air molecules and the smoke particles.(Produces a resultant force which is not constant but rapidly changing

Air molecules are constantly moving in rapid, random and continuousmotion.

Scenario: If large smoke particles were used.

There will be less haphazard movement because the randomness of theinvisible air molecules and the smoke particles would be averaged out.

Melting - process by which matter changes from solid to liquid at a constanttemperature (melting point) on hearting.

Boiling process by which matter changes from liquid to gas at a constanttemperature (the boiling point) on heating.

The heat supplied (the latent heat of fusion)-may increase the EP of molecules while average EK of molecules remain fairlyconstant (as temperature is constant)

The heat supplied (the latent heat of vaporisation) increases the EP of molecules and enables the molecules to do work in pushing backthe external pressure.

Evaporation process by which liquid changes into water vapour without boiling i.e.at any temperatures below its boiling point.

More energetic water molecules escape from the surface of the liquid,leaving behind the less energetic ones

So the average EK of the remaining molecules will decrease Temperature depends on the average EK of the molecules Since the average EK decreases, the temperature of the liquid will drop

and the liquid cools down thus causes cooling.

Rate of evaporation depends on The surface area of the liquid The temperature of the liquid The movement of air above the surface The nature of the liquid Humidity amount of water vapour in the atmosphere

Stress and Strain

Tension forces act outwards in opposite directions and tend to lengthen the body.

Compression forces act inwards in opposite directions and tend to shorten thebody.

Shear forces act in opposite directions along parallel faces, producing a tendencyfor parallel sections of the body to slide.


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Torsion a type of shearing which twists the body lengthwise.

Stress Force applied per unit cross-sectional area.

Strain extension per unit original length

Young Modulus ratio of stress to strain

Hookes Law states that force is proportional to the extension.

Elastic Deformation the material returns to original shape (length) once theapplied force is removed.

Plastic Deformation the material does not return to its original shape (length)once the applied force is removed and is permanently deformed.

Ultimate Tensile Stress is the maximum stress that can be applied to a materialbefore it breaks.

Hysteresis the stress-strain graph for loading is different from that for unloading.Energy is absorbed in a loading / unloading cycle.

Creep describes the very slow change in length or shape of certain metals evenwhen the applied stress does not change.

Effect seems to depend on temperature.

Fatigue - describes the fracture which sometimes occurs in metal samples after theyhave been subjected to a very large number of stress cycles.

Waves

There are two types of waves:1) Progressive/Travelling

-waves which moves energy from place to place-They allow transfer of energy-consists of a disturbance moving from a source to surrounding places as aresult of which energy is transferred from one place to another.

2) Stationary / Standing do not travel along the medium

There are two types of stationary waves: Mechanical waves produced by a disturbance (e.g. a vibrating body) in a

material medium and are transmitted by the particles of themedium oscillating to and fro.-can be seen or felt

Electromagnetic waves are oscillating of electric and magneticfields in space (no medium is required)

Two types of waves differ by how it travels :


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Transverse waves waves where the particle movement is atright angles to the direction of propagation of waves.

-have crests and troughs

Longitudinal waves are waves where the particle movement isparallel (in the same direction) to the propagation of waves.

-have compressions and rarefactions.

Amplitude magnitude of the maximum value of the displacement if the particlefrom its rest position.

Wavelength the smallest distance between two points which are in phase with eachother.

Period is the time taken for one complete oscillation.

Frequency - number of cycles passing a point per unit time of the source on the waveor of the point of the wave.

Wave front - a line showing the position of the crest s of a wave A line or surface on which the disturbance is in phase at all points.

Phase difference is a measure of a fraction of a cycle (or an oscillation) a particularpoint or wave is ahead or behind another point.

Coherence constant phase difference between the two waves.

Wave speed distance travelled per second by its wave crests.

Polarisation a wave property possessed only by transverse waves by which theyare made to vibrate in a particular place.

Polariser - a piece of transparent material (e.g. Polaroid) or device which will onlyallow the vibrations in a certain plane to pass through.

Why transverse waves are only possible to be polarised:-Vibration in all possible directions-Longitudinal however, vibration is in direction of wave travel.

Conditions : vibrations are in one plane only which contains thedirection in which the wave is travelling

Purpose: single direction of oscillation

Application : -Reduces glare from reflecting surfaces-Stress analysis-Poor TV reception

Diffraction bending of waves or spreading of waves as it passes through anaperture or at an edge.


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Principle of Superposition When two or more waves meet at the same place atthe same time the resultant displacement is equal to thevector sum of the individual displacements of the waves atthat point.

Uses of Superposition 1) Fibre optics2) Musical notes

1) Interference and diffraction pattern

Interference when two or more coherent waves (having a constant phaserelationship) in the same region of space overlap, there is a change inoverall intensity or displacement.

Constructive interference at some points, when the waves are in phase with eachother, the resultant wave is of greater amplitude than any ofits constituents.

Destructive Interference at some points, when the waves are completely out ofphase with each other, the resultant wave cancels out.

For observable interference pattern:-both waves must be of the same type-waves must meet at a point-both wave sources must be close enough-both waves are polarised in the same plane-both waves must be coherent-the amplitude of two waves must be roughly the same

Otherwise :-completely dark fringe will never be obtained

-the contrast pattern is reduced

Conditions for constructive and Destructive patterns :1) For Bright Fringes

-path difference must be the whole number of wavelengths i.e.n

2) For Dark Fringes

-

Stationary waves formed when two progressive waves of the same speed,amplitude and frequency travelling (in the same medium) in oppositedirections meet.

2n+12


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Nodes position of destructive interference Where the amplitude is zero

Antinodes position of constructive interference Amplitude of vibration is maximum

End correction at an open end of a column, the antinodes are slightly above theend of the tube.

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(Phys)Compiled Definitions and Principles for ASlevel paper 1/Paper 2