Physics for students

Basics of GCE A Levels Physics (9702)

2017-09-22T17:08:00.000+01:00

Physical Quantity: Any measurable quantity is called Physical Quantity.

Base Quantity: The physical quantity that could be measured independently is called a base quantity.

I will be removing the phrase .........is called or ........is defined as ...

Derived Quantity: The physical quantity that depends upon other physical quantities for measurement.

Vector: The physical quantity that has both magnitude and direction.

Scalar: The physical quantity that has magnitude only.

Actually, vector means 'to carry' and scalar means 'of a scale', so if we try to learn through etymology we can learn the definitions easily.

Precision: The degree to which the observed values are least scattered.
The precision is the measure of goodness of data. Many of us may have misconception that precision has to do anything with the errors made by experimenter. During recording of data, we take a large number of data. Precision refers to the spread of data for at least one fixed parameter.

Accuracy: The degree to which the observed value approaches the true value.
The accuracy is based on the type of instrument we use. If a length is measured with a micrometer screw gauze the reading may be 1.738 cm, the same length recorded by vernier calipers is 1.74 cm and for meter rule it is 1.7 cm. Here the degree of accuracy is decreasing. Actually, the least count plays an important role on accuracy of the data.

Systematic Error: The error that arises due to known causes.
As the cause is known one can eliminate the error by proper adjustment of the instrument. Furthermore, if the reading has a error of same magnitude, it is a systematic error.

Random Error: The error that arises due to unknown causes.
As the cause is unknown, it can't be removed; but one can minimize the error by taking multiple readings for a parameter and taking the average value.

SOLVED PAPER ON QUANTUM MECHANICS (9702)

2015-10-25T04:16:00.001+00:00

Though Quantum Mechanics is very interesting we find it difficult during our examinations. I have tried to solve the questions of Quantum Mechanics and Radioactivity of GCE A Levels( 9702). Click the link Solved Paper of Quantum Mechanics 9702 to download the solved paper.

MUST KNOW FACTS I

2013-06-01T11:08:00.002+01:00

Sunlight exerts pressure (solar radiation pressure).

On average, our bodies constantly resist an atmospheric pressure of about 1kg per square cm. Thanks to blood pressure otherwise I wouldn't have been writing this.

Due to the effect of Thermal Expansion, the Eiffel Tower is upto 15cm taller in summer.

If an atom were the size of a stadium, its electrons would be as small as bees. Comparable dimensions!!

If given the same mass, our body would actually be hotter than the Sun. The continuous conversion of chemical energy to thermal energy.

The only rock that floats in water is pumice. Its an igneous rock.

INTERFERENCE

2013-04-11T07:28:00.004+01:00

In Young's Double Slit experiment following changes are observed if we change the parameters in following way:

DOUBLE SLIT ARRANGEMENT

INTERFERENCE AND FRINGE FORMATION

1. If wavelength of the incident light is increased the fringe spacing will be increased as it is directly proportional to the wavelength of the incident light but the contrast between the bright and dark fringes will not be affected.

2. If the double slit separation is increased the fringe spacing will be reduced as it is inversely proportional to the double slit separation but the contrast between the bright and dark fringes will not be affected.

3. If the distance from the double slits to the screen is increased the fringe spacing will be increased as it is directly proportional to distance between the double slit and screen but the contrast between the bright and dark fringes will be reduced as the intensity of the bright fringes will be reduced.

PHYSICS FACTS

2012-09-17T11:15:00.001+01:00

No Physicist has ever seen ELECTRON.

Mass and Inertia resemble eachother.

Momentum is conserved in all types of collision.

The slope of velocity-time graph is acceleration.

ELECTRON VOLT is the unit of energy which is commonly used to estimate the smaller energy values.

An unbalanced object must produce acceleration.

Sound waves are longitudinal and mehanical wave.

Magnetic Resonance Imaging MRI

2012-01-14T04:49:00.001+00:00

Magnetic resonance imaging (MRI), nuclear magnetic resonance imaging (NMRI), or magnetic resonance tomography (MRT) is a medical imaging technique used in radiology to visualize detailed internal structures. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body.
An MRI machine uses a powerful magnetic field to align the magnetization of some atomic nuclei in the body, and radio frequency fields to systematically alter the alignment of this magnetization. This causes the nuclei to produce a rotating magnetic field detectable by the scanner—and this information is recorded to construct an image of the scanned area of the body. Magnetic field gradients cause nuclei at different locations to rotate at different speeds. By using gradients in different directions 2D images or 3D volumes can be obtained in any arbitrary orientation.
MRI provides good contrast between the different soft tissues of the body, which makes it especially useful in imaging the brain, muscles, the heart, and cancers compared with other medical imaging techniques such as computed tomography (CT) or X-rays. Unlike CT scans or traditional X-rays, MRI does not use ionizing radiation.
Click the link to download the file on MRI for A2 of Cambridge GCE A levels course. notes on MRI

Interpretation Of Graphs

2011-08-17T18:51:00.000+01:00

On a displacement-time graph …
-slope equals velocity.
-the "y" intercept equals the initial displacement.
-when two curves coincide, the two objects have the same displacement at that time.
-straight lines imply constant velocity.
-curved lines imply acceleration.
-an object undergoing constant acceleration traces a portion of a parabola.
-average velocity is the slope of the straight line connecting the endpoints of a curve.
-instantaneous velocity is the slope of the line tangent to a curve at any point.
-positive slope implies motion in the positive direction.
-negative slope implies motion in the negative direction.
-zero slope implies a state of rest.
-The area under the curve is meaningless

On a velocity-time graph …
-slope equals acceleration.
-the"y" intercept equals the initial velocity.
-when two curves coincide, the two objects have the same velocity at that time.
-straight lines imply uniform acceleration.
-curved lines imply non-uniform acceleration.
-an object undergoing constant acceleration traces a straight line.
-average acceleration is the slope of the straight line connecting the endpoints of a curve.
-instantaneous acceleration is the slope of the line tangent to a curve at any point.
-positive slope implies an increase in velocity in the positive direction.
-negative slope implies an increase in velocity in the negative direction.
-zero slope implies motion with constant velocity.
-the area under the curve equals the change in displacement.

On an acceleration-time graph …
-slope is meaningless.
-the"y" intercept equals the initial acceleration.
-when two curves coincide, the two objects have the same acceleration at that time.
-an object undergoing constant acceleration traces a horizontal line.
-zero slope implies motion with constant acceleration.
-the area under the curve equals the change in velocity.

NIKOLA TESLA

2011-03-27T15:08:00.003+01:00

Nikola Tesla (10 July 1856 – 7 January 1943) was an inventor and engineer. He was an important contributor to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Tesla's patents and theoretical work formed the basis of modern alternating current (AC) electric power systems, including the polyphase system of electrical distribution and the AC motor. This work helped usher in the Second Industrial Revolution.

Since the Nobel Prize in Physics was awarded to Marconi for radio in 1909, Thomas Edison and Tesla were mentioned in a press dispatch as potential laureates to share the Nobel Prize of 1915, leading to one of several Nobel Prize controversies. Some sources have claimed that because of their animosity toward each other neither was given the award, despite their scientific contributions; that each sought to minimize the other's achievements and right to win the award; that both refused to ever accept the award if the other received it first; and that both rejected any possibility of sharing it.

In the years after these rumors, neither Tesla nor Edison won the Prize (although Edison did receive one of 38 possible bids in 1915, and Tesla did receive one bid out of 38 in 1937).Earlier, Tesla alone was rumored to have been nominated for the Nobel Prize of 1912. The rumored nomination was primarily for his experiments with tuned circuits using high-voltage high-frequency resonant transformers.

In his honour the unit of magnetic flux density is TESLA (T).

Electron

2011-02-16T05:31:00.001+00:00

Question: What is the definition of electron? Even electron or proton has charge, what does it mean?
By Anjani Yadav
Answer:
The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure. Therefore, the electron is generally believed to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton.

In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles.

Electric charge is a physical property of matter which causes it to experience a force when kept near to other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. Positively charged objects and negatively charged objects experience an attractive force. As electron and proton both experience a force (either attractive or repulsive) they are called charged particles.

Archimedes

2011-02-12T04:31:00.000+00:00

Archimedes of Syracuse (Greek: Ἀρχιμήδης; c. 287 BC – c. 212 BC) was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an explanation of the principle of the lever. He is credited with designing innovative machines, including siege engines and the screw pump that bears his name. Modern experiments have tested claims that Archimedes designed machines capable of lifting attacking ships out of the water and setting ships on fire using an array of mirrors.

Archimedes is generally considered to be the greatest mathematician of antiquity and one of the greatest of all time. He used the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of pi. He also defined the spiral bearing his name, formulae for the volumes of surfaces of revolution and an ingenious system for expressing very large numbers.

Work-Energy principle

2011-02-12T04:10:00.002+00:00

Question: Heavy ball is dropped from heights 50cm,1m, 2m. In which situation the depression would be maximum and why? By Deepak Yadav

Answer:
The potential energy possessed by ball in different heights in ascending order is when it is at 50cm,1m,2m respectively.So when the ball falls from height of 2m it will lose more potential energy than the ball dropped from 50cm or 1m.So ball dropped from 2m height will cause maximum depression.

ELECTRICITY (CHARGE)

2011-02-07T14:23:00.000+00:00

Charge ( Q)
On the sub-atomic level we have a unit of charge of 'e' , the charge on the electron. This has the value −1.602×10^-19C. Similarly, a proton has a charge of +1.602×10^-19C .
The macro unit of charge in electricity is the Coulomb (C). It is quite a large unit and has approximately the same charge as 1.602×10^-19 electrons(or protons).
By definition the Coulomb is defined as: the charge that passes an arbitrary fixed point when a current of 1 Ampere flows for 1 second.

Current (I)
Electric current can be thought of as a flow of charged particles. In the normal case, when charge flows through wires these particles are electrons. However, when current flows in a vacuum, a solution or a melt, the charge carriers are ions. In semiconductors the charge carriers are exotic particles called 'holes'.
By definition the Ampere (A) is defined as: the current that passes an arbitrary fixed point when a charge of 1 Coulomb flows for 1 second.
Since,
   amount of fluid = rate of flow x time
by analogy,
   charge = electric current x time
   (Coulombs) = (Amperes) x (seconds)
   Q = It
Potential Difference (V)

Potential difference is short for potential energy difference. Our definition of the volt relates charge and the work needed to move that charge between two points.
In our definition of the volt, the charge is 1 Coulomb and the work done is 1 Joule.
Hence the definition : Two points A & B are at a potential difference of 1 volt if the work required to move 1 coulomb of charge between them is 1 Joule.

A simple analogy is gravity. Compare the energy difference between a rock at the bottom of a cliff and the energy in moving it to the top of the cliff. An energy difference exists between the top of the cliff and the bottom. The amount of energy difference depends on the size of the rock and the height of the cliff (P.E. = mgh) .
In our analogy, height relates to potential difference and rock weight relates to the amount of charge. Work is done on the rock against the force of gravity. Work is done on the charge in moving it against an electrostatic force.
The volt has unit of joules per coulomb (J/C ).
We now have an equation linking work/energy W, charge Q and potential difference V :

work = charge x potential difference
(Joules) = (Coulombs) x (volts)

Resistance (R)
By definition, the electrical resistance (R) of a conductor is the ratio of the p.d. (V) across it to the current (I) passing through it.

From this equation, by making each quantity unity, we define the Ohm:
The resistance of a conductor through which a current of 1 ampere flows when a p.d. of 1 volt exists across it.

Note in the diagram, the voltmeter is in parallel with the resistance, while the ammeter is in series.
Some conductors/devices have variable resistances which depend on the currents flowing through them.

These are all non-ohmic conductors except for the bottom right graph. Ohmic conductors are all metals and follow Ohm's Law.

Ohm's Law

The current through a resistor is varied, while the p.d. across it is measured. The graph of V against I is a straight line through the origin.

Hence,

Ohm's law states: The current through a conductor is directly proportional to the p.d across it, provided physical conditions are constant.

Gaspard-Gustave de Coriolis

2011-01-29T10:43:00.000+00:00

Gaspard-Gustave de Coriolis or Gustave Coriolis (21 May 1792 – 19 September 1843) was a French mathematician, mechanical engineer and scientist. He is best known for his work on the supplementary forces that are detected in a rotating frame of reference, and one of those forces nowadays bears his name. Coriolis was the first to coin the term "work" for the transfer of energy by a force acting through a distance.

In 1829 Coriolis published a textbook, Calcul de l'Effet des Machines ("Calculation of the Effect of Machines"), which presented mechanics in a way that could readily be applied by industry. In this period the correct expression for kinetic energy, ½mv², and its relation to mechanical work became established.

DC CIRCUITS 2

2011-01-24T06:26:00.001+00:00

Kirchoff 's First Law:At any junction in a circuit, the sum of the currents arriving at the junction is equal to the the sum of the currents leaving the junction.

Conservation of Charge and the Kirchoff 's First Law: Kirchhoff's first rule is a statement of conservation of electric charge. All charges that enter a given point in a circuit must leave that point because charge cannot build up(accumulate) at a point. If this does not happen then charges are getting accumulated at a point or charges are created from nowhere! both of which don't happen. In other words - charge is conserved.

The current entering any junction is equal to the current leaving that junction. i₁ + i₄ = i₂ + i₃

The law can also be stated as:-The algebraic sum of currents meeting at a junction is zero.
CURRENT Medical Diagnosis and Treatment 2011 (LANGE CURRENT Series)

DC CIRCUITS 1

2011-01-23T08:49:00.000+00:00

Conservation of charge:The net charge of an isolated system remains constant.Charge can be created and destroyed, but only in positive-negative pairs.

It is not possible to destroy or create charge.

You can cancel out the e ect of a charge(or neutralize the charge on the body) on a body by adding an equal and opposite charge to it, but you can't destroy the charge itself.

The following example makes this clear

If a glass rod is rubbed with a silk cloth, due to friction the glass gets charged positively and the silk negatively.The charging is basically due to the transfer of negative charge(electrons) from the glass to the silk.This experiment suggests that:- Charge is transfered but not created or destroyed.

The total charge on the Glass silk cloth system remains the same i.e zero before rubbing and after rubbing.

This will be continued in next day.

Fundamentals of Dc and Ac Circuits

A level Practical Check list

2011-01-22T11:52:00.002+00:00

A-Level Practical Support booklet

Newton Vs. Einstein

2011-01-22T09:27:00.000+00:00

All the physicists are playing hide and seek. Einstein is the ‘den’ and stands against the wall with his eyes closed and counts till 100 to enable all the physicists to run and hide. At the count of 100 Einstein turns around and finds Newton standing there.
He screams, “Newton, you are out!” Newton says, “No, I ‘m not!”
Einstein says, “Yes, you are. I can see you here in front of me”.
Newton says, “I’m not out. Pascal is.”
Einstein is a bit confused and starts to scratch his head and beard.
Newton says “Here, Let me explain”
He draws a square one meter by one meter on the floor and stands in the middle of it and says,
“Newton per meter square is a Pascal, so it’s Pascal who’s out not me”

Center of Gravity

2011-01-20T10:12:00.004+00:00

Question: I am facing the problem in understanding center of gravity.By Vikash Jha
Answer:
Center of gravity is the mean location of the gravitational force acting on a body. Technically it is the point on a body in which the entire weight is supposed to be concentrated.

The term center of mass is often used interchangeably with center of gravity, but they are physically different concepts. They happen to coincide in a uniform gravitational field, but where gravity is not uniform, center of gravity refers to the mean location of the gravitational force acting on a body. This results in small but measurable gravitational torque that must be accounted for in the operation of artificial satellites.

Charles De Coulomb

2011-01-20T09:45:00.001+00:00

Charles-Augustin de Coulomb (14 September 1736 – 23 August 1806) was a French physicist. He is best known for developing Coulomb's law, the definition of the electrostatic force of attraction and repulsion. The SI unit of charge, the coulomb, was named after him.

MAX PLANCK

2011-01-18T04:48:00.000+00:00

Max Karl Ernst Ludwig Planck (April 23, 1858 – October 4, 1947) was a German physicist who is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics in 1918.

Planck was born in Kiel, Holstein, to Johann Julius Wilhelm Planck and his second wife, Emma Patzig. In 1867 the family moved to Munich, and Planck enrolled in the Maximilians' gymnasium school, where he came under the tutelage of Hermann Müller, a mathematician who took an interest in the youth, and taught him astronomy and mechanics as well as mathematics. It was from Müller that Planck first learned the principle of conservation of energy. Planck graduated early, at age 17.This is how Planck first came in contact with the field of physics.

The Munich physics professor Philipp von Jolly advised Planck against going into physics, saying, "in this field, almost everything is already discovered, and all that remains is to fill a few holes." Planck replied that he did not wish to discover new things, only to understand the known fundamentals of the field, and began his studies in 1874 at the University of Munich. Under Jolly's supervision, Planck performed the only experiments of his scientific career, studying the diffusion of hydrogen through heated platinum, but transferred to theoretical physics.

In his honour a constant is named after him called Planck's constant. The Planck constant (denoted h), also called Planck's constant, is a physical constant reflecting the sizes of quanta in quantum mechanics. It is name after Max Planck. Its value is 6.62606896 × 10⁻³⁴ J·s.

Two theories of relativity

2011-01-16T08:53:00.004+00:00

Question: What is the main theme of the Einstein's theories of relativitiy? By Prabesh Acharya
Answer:
Special Theory of Relativity is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies". It generalizes Galileo's principle of relativity—that all uniform motion is relative, and that there is no absolute and well-defined state of rest (no privileged reference frames)—from mechanics to all the laws of physics, including both the laws of mechanics and of electrodynamics, whatever they may be. Special relativity incorporates the principle that the speed of light is the same for all inertial observers regardless of the state of motion of the source.
Special theory of relativity gives good account on length contraction,time dilation,addition of velocities and above all mass-energy equivalence.

General Theory of Relativity is the geometric theory of gravitation published by Albert Einstein in 1915. It is the current description of gravitation in modern physics. General relativity generalises special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or space-time. In particular, the curvature of spacetime is directly related to the four-momentum (mass-energy and linear momentum) of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.
General relativity predicts that the path of light is bent in a gravitational field; light passing a massive body is deflected towards that body. This effect has been confirmed by observing the light of stars or distant quasars being deflected as it passes the Sun.

AMAZING FACTS 2

2011-01-15T06:26:00.002+00:00

The quark, a building block of the proton, got its name from James Joyce's Finnegans Wake, from the line "Three quarks for Muster Mark! Sure he hasn't got much of a bark".
It is not true that Einstein was a terrible student as a youth. While he was slow to learn to speak before entering school and did poorly at French while in school, his academic records indicate that he was a child prodigy who understood college physics before his eleventh birthday, a strong violin player, and skilled in Latin and Greek.
The inventor of the electric light was not Thomas Edison. In 1802, 77 years before Edison perfected a filament for the incandescent lamp, Davy caused a platinum wire to glow by passing an electric current through it.

Time Dilation:clock running slower than actual

2011-01-15T05:19:00.001+00:00

Question: When one of the twins travelling in a spaceship with velocity 0.99 of c(velocity of light),returns to the earth he finds that he is younger than the other.What will be the case if the frame of reference is set on the one who is travelling in the spaceship? By Suman Acharya ,St. Xaviers' College

Answer:
This is the case of time dilation which is the outcome of special theory of relativity.For the moving observer it appears that the stationary clock is moving at a slow rate i.e. the time is dilated.Significant point to note is that if we fix the clock in the moving system and observer is in stationary system even then the conclusion is the same i.e. the observer reports that the clock is running slow as compared to his own.Similarly,if the state of affairs be reversed,observer would again report the same thing.So,by recording the time on a clock fixed in a certain system by an observer fixed in another system,it is difficult to distinguish which one of the systems is stationary or in motion;only a relative motion should be accounted.These observed facts lead to the Principle of equivalence.

AMAZING FACTS 1

2011-01-14T06:50:00.001+00:00

In 1905 Albert Einstein wrote his famous Special Theory of Relativity. It was published in a scientific journal that same year, but took many years to gain general acceptance. In fact, it was not verified by actual experiment until 25 years later. Two years after that paper was published, Einstein wanted a job as assistant professor of mathematics. This job required the applicant to submit a thesis paper, so Einstein submitted his Special Theory of Relativity. The university rejected it.
According to the laws of gravity, the moon technically does not orbit the Earth. The two bodies actually both orbit around their common centre of gravity, which is located 1,000 miles beneath the surface of the Earth and is on a straight line between the centres of the Earth and moon. The centre of the Earth makes a small circle around that centre of gravity every 27 ¹/₃ days.
Light has weight. The weight of sunlight on the earth's surface has been determined to be two pounds per square mile.

E =MC^2

2011-01-14T05:15:00.001+00:00

Question:What is the meaning of usinfg C^2 as a constant in E=mc^2? By Lenin Gautam.

Answer:
This question needs special reference to Einstein's Special theory of Relativity.
In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept the total internal energy E of a body at rest is equal to the product of its rest mass mand a suitable conversion factor to transform from units of mass to units of energy. If the body is not stationary relative to the observer then account must be made for relativistic effects where m is given by the relativistic mass and E the relativistic energy of the body.
There is a slight misunderstanding from most of the students about mass-energy equivalence.
The concept of mass–energy equivalence connects the concepts of conservation of mass and conservation of energy, which continue to hold separately. The theory of relativity allows particles which have rest mass to be converted to other forms of mass which require motion, such as kinetic energy, heat, or light. However, the mass remains. Kinetic energy or light can also be converted to new kinds of particles which have rest mass, but again the energy remains. Both the total mass and the total energy inside a totally closed system remain constant over time, as seen by any single observer in a given inertial frame. In other words, energy cannot be created or destroyed, and energy, in all of its forms, has mass. Mass also cannot be created or destroyed, and in all of its forms, has energy. According to the theory of relativity, mass and energy as commonly understood, are two names for the same thing, and neither one is changed or transformed into the other. Rather, neither one appears without the other. Rather than mass being changed into energy, the view of relativity is that rest mass has been changed to a more mobile form of mass, but remains mass. In this process, neither the amount of mass nor the amount of energy changes. Thus, if energy changes type and leaves a system, it simply takes its mass with it. If either mass or energy disappears from a system, it will always be found that both have simply moved off to another place.