PHYSICS Definitions and NOTES

[Newbie]

AS Level Physics: Terms & Definitions:-

Mechanics:-

Displacement: Distance moved in a particular direction.

Speed: The distance travelled per unit time.

Velocity: The distance travelled in a particular direction/ the displacement per unit time.

Acceleration: The rate of change of velocity.

Acceleration Of Free Fall: The acceleration on an object when the only force acting on it is the gravitational pull of the Earth.

Free Fall: The downward motion of an object under the influence of force of gravity with a constant acceleration (g = 9.81 ms-2).

Newton’s First Law Of Motion: An object will maintain uniform velocity or remain stationary unless an external force acts upon it.

Newton’s Second Law Of Motion: The acceleration of an object is directly proportional to the resultant force acting on it in the same direction. (F = m x a)

Newton’s Third Law Of Motion: Every action has an equal and opposite reaction. (If one body exerts a force on another, it will experience a force by the other body, which is equal in magnitude & opposite in direction.)

Mass: It is a measure of inertia of a body or It is a body’s reluctance to undergo linear acceleration.

Weight: It is the gravitational force exerted on an object’s mass.

Momentum: It is the product of a body’s mass & velocity, with its direction always being the same as the body’s direction of velocity.

Force: It is defined as the rate of change of momentum of a body, or the product of a body’s mass & its acceleration.

Principle Of Conservation Of Momentum: The total momentum of a system remains constant before & after a collision, provided that no external force acts upon the system.

Elastic Collisions: A collision in which both the total momentum & the total Kinetic Energy of a system is conserved.

Inelastic Collisions: A collision in which the total momentum of a system is conserved, but the total Kinetic Energy is not conserved.

Upthrust: It is the resultant force on a submerged object due to the upward pressure of the fluid applied on it. It is also known as Buoyancy Force.

Centre Of Gravity: The point on an object at which the entire weight of the body seemingly acts. It is the point at which the Earth actually applies the pull of gravity.

Moment: It is the turning effect of a force. It is the product of the force & the perpendicular distance between the axis of rotation/pivot & the line of action of the force.

Torque Of A Couple: The turning effect caused by two equal & opposite forces when their line of actions are different.

Torque of a Couple = Magnitude of any one force x Linear Distance between the forces

The Principle Of Moments: The sum of clockwise moments taken about any point is equal to the sum of anti-clockwise moments taken about the same point when a system is in equilibrium.

Energy: It is the stored ability to do work.

Kinetic Energy: The energy possessed by an object by virtue of its motion.

Potential Energy: It is the energy possessed by an object by virtue of its position.

Gravitational Potential Energy: The energy possessed by an object due to the height raised above the ground/against the force of gravity.

Elastic Potential Energy: The energy possessed by an elastic object by virtue of its compression or expansion, due to elastic restoring force. (k x X)

Internal Energy: It is the total of the microscopic Kinetic & Potential energies of particles of a material.

Impulse: It is the product of a force & the time during which the force is applied.

Work: It is the product of a force & the distance moved in the direction of the force.

Power: It is the rate at which work is done. It is work done per unit time.

Power: It is the product of force & velocity.

Efficiency: It is the fraction of the useful power output obtained from the total power input.

 

[Newbie]

Matter:-

Density: It is the amount of mass per unit volume of a substance.

Brownian Motion: The haphazard or random movement of tiny suspended particles (such as smoke, pollen etc.) in a fluid is known as Brownian Motion.

It gives direct evidence for perpetual molecular movement. This experiment demonstrates the random haphazard movement of smoke particles in water as they collide with invisible particles of the medium itself.

Crystalline Solids: They have closely packed structures in a regular arrangement. Elastic strain is usually less than about 1%. Individual molecules move a small distance from their equilibrium position on application of a force & the return to their original equilibrium position once the force is removed. E.g. Diamond

Polymeric Solids: Solids with very long chains of molecules. The molecular chains are tangled up, & occasionally have cross-links between the chains. Hence, when a force is applied, then the strands can be pulled out to lie more parallel to one another. Some reorganization of the cross-links does take place, & therefore there can be permanent distortion as well. E.g. Rubber

Amorphous Solids: These differ from crystalline solids because they lack the crystalline arrangement of molecules. Any pattern or regularity that does occur in structure takes place over very short distances, of the order of a few molecular diameters. E.g. Glass & soot

Pressure: It is the perpendicular/normal force applied per unit area.

The Kinetic Theory Of Gases:

· Any gas consists of a very large number of molecules.
· The molecules are in rapid, random motion.
· Collisions between gas molecules are elastic.
· Collisions between molecules & the walls of the container are elastic.
· There are no intermolecular forces of attraction.
· Intermolecular forces of repulsion only act during collisions between the molecules. The duration of collisions as compared to the time interval between collisions is negligible.
· The volume that the molecules themselves take up is negligible in comparison to the volume of the container itself.

Melting: The process by which a solid changes into its liquid state at a constant specific temperature, known as melting point.

Boiling: The process by which a liquid changes into its gaseous state at a constant specific temperature, known as boiling point.

Evaporation: The process by which molecules on the surface of a liquid with sufficient Kinetic Energy break from the attractive intermolecular forces of the liquid & escape as gas particles. This process occurs below the boiling point of a liquid.

Stress: It is the force per unit area of cross-section required to stretch a material. It is sometimes called Tensile Stress, as forces can be applied in different ways to objects. E.g. Under compression, a compressive stress is applied. All stresses have the same formula & unit as pressure.

Strain: As a result of applying a tensile stress to an object, a tensile strain is set up within the object. Stress is the cause & strain is the effect. It is defined as the extension per unit length. It is a ratio of two lengths, & therefore does not have a unit. Temperature also effects strain.

Young’s Modulus: It is the ratio of stress to linear strain. It is also known as the modulus of elasticity.

Elastic Deformation: When a material is elastic, it returns to its original shape on removal of the distorting force. Elastic Deformation is temporary distortion. Most materials are elastic for low stresses.

Plastic Deformation: It is when a small increase in stress causes a large increase in the strain on an object. A material that receives deformation in this way is said to be ductile, meaning it has a large plastic region. Within the plastic region, it is more difficult to measure the strain at a particular value of stress.

Necking: In wires, when a sufficiently large force is applied, localized narrowing occurs at weak points, & the wire eventually breaks at one of these points.

Creep: Plastic distortion is time-dependant. For an applied stress, the initial strain will have a particular value, but if the strain is measured later, it is often found to have increased.

Area under a Force-Extension Graph: The area under such a graph is the work done in stretching a material. For the straight-line portion of the graph, it is a measure of the elastic potential energy stored by the material, provided that the graph for decreasing loads is the same as that for increasing loads. It is also known as strain energy.

Ductile Materials: Materials which undergo plastic deformation after a considerable elastic deformation. Ductile materials are used for wiring etc. E.g. copper

Brittle Materials: Materials which do not undergo plastic deformation. They undergo elastic deformation to a certain point & then break along cleavages within the material’s structure at the Breaking Point/Breaking Stress. E.g. china, marble

Polymeric Materials: Materials which can undergo great strain, & deform to a very great degree. E.g. rubber, glass, cement

Ultimate Tensile Stress: It is the maximum value of stress that an object can sustain before it breaks or cleaves.





Waves:-

Displacement: It is the change in position of an oscillating particle from its rest or mean position in a particular direction. It is a vector.

Amplitude: It is the magnitude of the maximum value of displacement. It is a scalar.

Phase Difference: If two oscillations are in step with one another, they are said to be in phase with one another. Oscillations are said to be in antiphase if they are always moving in opposite directions. For example; if the crest of one wave falls with the trough of another, then they are said to be out of phase by 180 degrees.

Period: The time taken to complete one oscillation.

Frequency: The number of oscillations per unit time. It is measured in Hertz (Hz). 1 Hz is one cycle per second.

Wavelength: It is the smallest distance between two points that are in phase with one another.

(Wave) Speed: It is the speed with which crests of the wave move or the speed with which energy is transferred. It is NOT the speed with which particles in the wave move.

The Transfer of Energy: The transfer of energy is due to a progressive wave, NOT a standing/stationary wave.

Transverse Waves: A wave in which displacement of particles is perpendicular to the direction of wave propagation, resulting in crests & troughs. E.g. light waves (the entire electromagnetic spectrum)

Longitudinal Waves: A wave in which displacement of particles is parallel to the direction of wave propagation, resulting in compressions & rarefactions. E.g. sound waves

Electromagnetic Waves: These are transverse waves. The displacement in the case of electromagnetic waves is a variation in the electric & magnetic fields perpendicular to each other.

Polarisation: As a result of the transverse nature of vibrations, transverse waves have an additional property that is not possessed by longitudinal waves. The movement of particles in transverse mechanical waves is at right angles to the direction of wave propagation. This, however, still leaves many possibilities for the direction of the particle in 3D. Frequently, oscillations take place in a transverse wave in many different directions, & the wave is said to be unpolarised. If the oscillation does take place in only one direction, however, the wave is then said to be polarized in that direction. That wave is then known as a plane-polarised wave.

Stationary Waves: A stationary wave is produced because of superposition of two waves of similar wavelength & amplitude, but travelling in opposite directions. A characteristic of a stationary wave is that there are some parts of the wave where the amplitude is always zero. The points are known as nodes. Halfway between the nodes, the amplitude is at its maximum, & these points are called antinodes. Energy is NOT transferred in standing waves.

Diffraction: The spreading of waves near an obstacle is called diffraction. If the width of the opening is comparable with a single wavelength, the magnitude of diffraction is large as compared with say, if the width of the opening was five wavelengths.

Diffraction Grating: It is a series of narrow parallel slits. If parallel monochromatic light waves approach a series of narrow slits close to one another, the waves from each slit are spread out over 180 degrees after passing the slits. It is the ability of a diffraction grating to give a dark background, where the intensity is near zero, that makes it useful for examining spectra.

Principle of Superposition Of Waves: When two waves of the same type with similar frequency & speed are in phase with each other, their total amplitude on joining together/adding together is the sum of their individual amplitudes.

Interference: When two waves superimpose, they cause interference. When the crests of both waves fall on each other, constructive interference is achieved & the displacement of particles is at its maximum value. If the crest of one wave falls on the trough of the other, destructive interference takes place & the displacement of particles is at its minimum value, or zero.

Coherence: If monochromatic light is used, only one wavelength is present, as compared to if white light was used. Since speed & frequency are the same, all imperfections within the wave occur simultaneously for both sources of the monochromatic light. Two waves maintaining a constant phase difference are said to be coherent.

Fringe Width/Separation: The separation between one bright fringe & the next bright fringe.

Conditions for Observing Two-Source Interference:

· The two waves should be of the same type. (Both transverse or longitudinal).
· They should almost similar wavelength or frequency.
· They should arrive at a point at the same time (superimposed).
· They should maintain a constant phase difference. (Coherent sources are required).



Electricity:-

Electric Field: It is the modified area or region around a charged object in which it can apply an electrostatic force of attraction or repulsion on a test charge. Electric field strength is force per unit positive charge.

Electric Current: It is the amount of charge flowing through a circuit per unit time or It is the rate of flow of charged particles.

Ampere: If a charge of 1 Coulomb passes through an electrical component per second, then the current maintained is 1 Ampere.

Potential Difference: The P.D across an electrical component is the energy converted from electrical to other forms of energy when unit charge passes through it.

Volt: One volt is the P.D between two points in a circuit in which one joule of energy is converted when one coulomb of charge passes from one point to the other.

Resistance: The ratio of P.D to the current for an electrical component at a particular time is known as its resistance.

Ohm: A resistor has a resistance of one ohm if a P.D of one volt is to be maintained, to allow a passage of one ampere of current.

Resistivity: The resistivity of a wire of a particular material is its resistance for unit length.

Coulomb: If a current of one ampere (6.25x1018 electrons) passes through a conductor, then the charge flowed is one Coulomb or It is the amount of charge required to maintain a current of one ampere in a conductor.

Ohm’s Law: The current through a metallic conductor is proportional to the P.D across it provided that its temperature remains constant.

Thermistor (NTC): A specific type of resistor, in which, as temperature increases, the magnitude of the resistor’s resistance decreases, & vice versa.

Electromotive Force: The e.m.f of any source of electrical energy is the energy converted into electrical energy per unit charge supplied. It has the same unit as P.D; the volt.

E.m.f & P.D: While e.m.f refers to the amount of energy converted into electrical energy per unit charge supplied, P.D refers to the amount of electrical energy converted into other forms of energy per unit charge supplied. The e.m.f of a source is equal to the potential difference across its terminals as the current approaches zero.

Effect of Internal Resistance on P.D & Output Power: The higher the internal resistance of the battery/cell, the lower the terminal P.D, & hence, the lower the output power as well. This is due to the equation V = E – Ir

Potentiometer: When a potential divider arrangement is used to compare e.m.fs of two sources, it is known a potentiometer.

Kirchhoff’s First Law: The algebraic sum of the currents at a junction is zero. In other words, charge cannot be created or destroyed.

Kirchhoff’s Second Law: Around any closed loop in a circuit, the algebraic sum of the e.m.fs is equal to the algebraic sum of the P.Ds. In other words, each & every point in a stable electrical circuit has a particular value of potential. Any gains in electrical energy of a charge must be balanced by corresponding losses of energy.

Kirchhoff’s First & Second Laws are in correspondence & actually are an appreciation of the Law of Conservation of Charge & the Law of Conservation of Energy respectively.

Nuclear Physics:-

The Atom: The simple model of the atom is made up of three sub-atomic particles: The proton (which is positively charged), the neutron (which is uncharged but equal in mass to the proton), & the electron (which is negatively charged & equal to the charge on the proton, but much smaller in size & mass).

Mass Number & Proton Number: The mass number (also known as nucleon number) of an atom is the number of protons & neutrons (collectively also known as nucleons) within its nucleus, whereas the proton number refers simply to the number of protons within the nucleus, which is consequently also the number of electrons (provided that the atom has no overall charge).

Isotopes: These are atoms of the same element which have the same proton number, but a different nucleon number, due to a change in number of neutrons in their nuclei.

Radioactive Decay: This spontaneous & random process refers to the decay of unstable isotopes of elements until they gain a stable atomic configuration, with the emission of either Alpha, Beta or Gamma radiation. There is no order to this process, nor is there a way to predict the decay, as is shown by fluctuations in every radioactive sample’s count rate.

Effect of Internal Resistance on P.D & Output Power: The higher the internal resistance of the battery/cell, the lower the terminal P.D, & hence, the lower the output power as well. This is due to the equation V = E – Ir

Potentiometer: When a potential divider arrangement is used to compare e.m.fs of two sources, it is known a potentiometer.

Kirchhoff’s First Law: The algebraic sum of the currents at a junction is zero. In other words, charge cannot be created or destroyed.

Kirchhoff’s Second Law: Around any closed loop in a circuit, the algebraic sum of the e.m.fs is equal to the algebraic sum of the P.Ds. In other words, each & every point in a stable electrical circuit has a particular value of potential. Any gains in electrical energy of a charge must be balanced by corresponding losses of energy.

 

[Newbie]

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[utsav156]

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[Newbie]

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[utsav156]

I didn't want to make another topic for this .... These ARE CHEMISTRY REVISION SITES ....




This is a well established site that provides quality revision notes in all aspects of AS/A Level Chemistry. You can search through the notes using a Google search engine, or enter the site via a menu system.
http://adf.ly/CyQR

This is a well organised site that has both notes and tests on many aspects of AS/A Level Chemistry. Questions are ‘marked' online and correct answers given.
http://adf.ly/l8tk

This site contains notes and examination tips. They are written by Dr Rod Beavon of Westminster School and are appropriate for the AS/A Level Chemistry.
http://adf.ly/l8tl

Notes on a number of topics relevant to AS/A Level Chemistry are included. The notes include a particularly good interactive Periodic Table. There is also access to Homework Help and to a Midnight Café chat-room.
http://adf.ly/l8tm

This is a US site intended for first year undergraduates, but much is relevant to AS/A Level Chemistry. Notes, articles and tutorial are included. A number of experiment simulations can be accessed. The compound library is very good.
http://adf.ly/l8tn

A lighthearted look at many aspects of Chemistry. There are a lot of links to useful pages written by teachers and students. Not all of this is relevant to AS/A Level, but much is. A wealth of information and a lot of fun.
http://adf.ly/l8to

A high quality interactive Periodic Table with photographs and information about each element.
http://adf.ly/l8tp

A gallery of 3-D images representing atomic orbitals and molecular orbitals. Stunning images with comprehensive notes.
http://adf.ly/l8tq

This site provides absorption and emission spectra for any element selected from the Periodic Table.
http://adf.ly/l8tr

A structured revision guide to the main topics in AS/A Level Chemistry with extensive notes and sample questions. Very good for examination preparation.
http://adf.ly/l8ts

An interactive site allowing students to pose questions and receive answers. There is an extensive list of previous questions and answers that can be accessed and searched. The site includes a student chat-line.

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[Newbie]

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