Light...

Types of Light

To understand light you have to know that what we call light is what is visible to us.Visible light is the light that humans can see. Other animals can see different types of light. Dogs can see only shades of gray and some insects can see light from the ultraviolet part of the spectrum. The key thing to remember is that our light is what scientists call visible light. 

Scientists also call light electromagnetic radiation. Visible light is only one small portion of a family of waves called electromagnetic (EM) radiation. The entirespectrum of these EM waves includes radio waves, which have very long wavelengths and both gamma rays and cosmic rays, which are at the other end of the spectrum and have very small wavelengths. Visible light is near the middle of the spectrum. 

It's all Energy

The key thing to remember is that light and EM radiation carry energy. Thequantum theory suggests that light consists of very small bundles of energy/particles; it's just that simple. Scientists call those small particles photons, and the wavelength determines the energy and type of EM radiation, and the number of photons tells you how much radiation there is. A lot of photons give a brighter, more intense type of light. Fewer photons give a very dim and less intense light. When you use the dimmer switch on the wall, you are decreasing the number of photons sent from the light bulb. The type of light is the same while the amount has changed. 

Different Speeds of Light?

As far as we know, all types of light move at one speed when in a vacuum. The speed of light in a vacuum is 299,792,458 meters per second. That speed is really fast, but even when you're traveling that fast, it takes a while to get places in space. It takes about seven minutes for light from the Sun to reach Earth. It takes over four years for the light from our Sun to get to the nearest star. It would take a particle of light over 100,000 years to get from one side of our galaxy to the other side. All of those values are light moving through a vacuum. You can slow light down in other substances such as the atmosphere, water, or a diamond. Light moves at about 124,000,000 meters per second (less than half the speed in a vacuum) in a diamond. 

Analysing linear motion

Distance     : length between two points in a straight line or 
     
               length moved through a definite path.


Displacement : Distance moved in a definite direction (vector    


               quantity).


Speed        : distance moved per unit time.


Velocity     : rate of change in displacement.


Average speed: (total distance/total time)


                Average velocity (total displacement/ total time)


Constant velocity: rate of change in displacement is constant 
                   (zero acceleration).


                   Positive acceleration means that the velocity        


                   is increasing.


                   Negative velocity means that the acceleration  


                   is negative and the velocity decreases.


Period, T, 
is the time taken for a complete oscillation. Unit: s-1


Frequency,f, is the number of oscillations made in one second. Unit: Hz


A ticker timer is used to measure a short period of time in linear motion. One dot is the period of time taken between two consecutive dots on a ticker tape. If the frequency used is 50 Hz, the period for one dot is then 0.02 s.


A stroboscope is used to 'freeze' the motion of an oscillation to determine its frequency, where frequency of the oscillation equals frequency of stroboscope.


Frequency of stroboscope = number of slits X frequency of rotation.

Distance, Displacement, Velocity, Speed and Acceleration

Distance and Displacement

Distance is the total path length traveled from one location to another. It is a scalar quantity.

Displacement is the distance between two locations measured along the shortest path connecting them, in specified location. It is a vector quantity. The SI unit of distance and displacement is metre (m).

Speed and Velocity

Speed is the distance traveled per unit time or the rate of change of distance.

Speed = total distance traveled / time taken

Velocity is the speed in a given direction or the rate of change of displacement.

Average velocity = displacement/ time taken

Acceleration and Deceleration

Acceleration is the rate of change of velocity.

Acceleration = change of velocity / time taken

Change of velocity = final velocity (v) – initial velocity (u)

Acceleration = (final velocity – initial velocity) / time taken
  = (v – u) / t

Things to remember:

1. Constant velocity means the object is not accelerating. Acceleration is zero.
2. Constant acceleration means the object is increasing its velocity.

Newton's Three Laws of Motion

Newton's First Law

An object at rest continues its states of rest and a moving object will continue
to move with a constant velocity unless acted upon by a resultant force.

Newton's Second Law

The rate of change of momentum of an object is directly proportional to the resultant force acting on it and is in the direction of the force.

Newton's Third Law

Every action has an equal and opposite direction.


This is the simplified version of Newton's Three Laws of Motion Explanation. It may give you mark but no full marks.

Understanding Inertia

SITUATION 1

Have you ever stood in a bus which starts suddenly from rest? You are likely to fall backwards. If the moving bus stops suddenly, you are likely to fall forward.

SITUATION 2

Have you noticed that a bigger vehicle (Truck) is more difficult to stop than a light vehicle (Motorcycle)?

What Causes This to Happen?

Explanation:

When the bus moves suddenly from rest, our feet are carried forward but the inertia of our body tends to keep us at rest. This causes our body to fall backwards. When the bus stops suddenly, our feet are brought to rest, but the inertia of our body tends to continue its forward motion. This causes our body to fall forward.

The two situations above show that our body has an inbuilt resistance to any change in its state of rest or motion. This reluctance is called inertia.

“The inertia of an object is the tendency of the object to remain at rest or, if moving, to continue its uniform motion in a straight line.”

The concept of inertia was explained by Sir Isaac Newton in the first law of motion.


MASS AND INERTIA

It is to be put in mind that inertia is dependent upon the mass of the object. The larger the mass, the larger its inertia. Hence, we can see that its harder to push a heavy box than to push a lighter box.


EFFECTS OF INERTIA

Many phenomena in our daily lives involve inertia. We make use of the positive effects of inertia to solve some of our daily problems. On the other hand, there are many negative effects of inertia that can endanger our lives and wee need to find ways to reduce them.

Examples are: It’s more effective to fit the head of a hammer (with a higher mass) tightly onto the wooden handle by hitting the bottom of the handle against a hard surface. The head which has a larger mass remain in its state of motion and thus presses itself more tightly around the handle.

Inertia also can be observed in ice skaters where inertia enables ice skaters to keep gliding over the surface of ice at an almost constant speed in a straight line effortlessly.

Ways to reduce inertia in vehicle:

1. Seat belts help to tighten the passenger during collision. This is to prevent the passenger from being thrown forward due to inertia.

2. Air bag is fitted inside the steering wheel. It provides a cushion to prevent the driver from hitting the steering wheel.

Analysing Momentum

The momentum of an object is the product of its mass and its velocity.

p = m X v

The principles of conservation of liner momentum states that the total linear momentum of a closed system is constant.

The linear momentum before and after a collision is conserved if there is no external force acting on it.

Elastic collision: linear momentum, kinetic energy and total energy are conserved.

Inelastic collision: only linear momentum and total energy are conserved and there is a loss in kinetic energy.

In an EXPLOSION, where two objects move in opposite directions, the total linear momentum before and after the explosion is zero.

The acceleration of a rocket leaving the earth increases because:
a) its mass is decreasing.
b) air resistance is decreasing.
c) gravitational pull is decreasing.

Analysing Momentum II

Conservation of Momentum

1. The term conservation is derived from the root word “conserve” which means constant.
2. The principle of conservation of momentum states that in the absence of an external force, the total momentum of a system remains unchanged.
3. An example of external force is friction and this can be contact friction or air friction.
4. An isolated or closed system the sum of external forces is zero, thus, the principle of conservation of momentum is true for a closed system.

Collisions

1. There are two types of collision:
(a) Elastic collision
(b) Inelastic collisions

2. In Elastic collision: Two objects collide and move apart again after a collision. Momentum is conserved. Total energy is conserved. Kinetic energy is conserved.
Formula: m1u1+m2u2 = m1v1+m2v2

Elastic Collision

3. In Inelastic collision: Two objects combine and stop or move together with a same velocity after a collision. Momentum is conserved. Total energy is conserved. Kinetic energy is not conserved (the total kinetic energy after the collision is less than the total kinetic energy before collision, excess energy is released as heat, sound energy etc).
Formula: m1u1+m2u2 = (m1+m2)v

Inelastic Collision

Impulse and Impulsive Force

1. Impulse is defined as the change momentum
2. From F=ma
  Ft=mv-mu (change of momentum)
3. Impulse is the product of the force F acting on a body and the time t for which the force acts.
Hence, impulse = Ft = mv – mu
4. The SI unit of impulse is kg m s⁻1 or N s.
5. Impulsive force is the rate of change of momentum.
  Impulsive force = Impulse / time
6. The SI unit of impulse is kg m s⁻² or N.
The Effect of Time on an impulsive Force
1. From the formula for impulsive force, we get
Ft = mv – mu
F =  (mv - mu) / t
This shows that the time of action is very important factor in the calculation of the impulsive force.
2.When the time of action is prolonged, the impulsive force will decrease.
3. On the other hand, if the time of action is shortened, the impulsive force will increase.


Ways to Reduce Impulsive Forces
The Design of a car
1. A car is mainly designed for the safety of the driver.
2. The front and the rear parts of the car are made of soft metal so that the car is easily crumpled during an accident.
a) During collision, the time taken for the change in speed (from a high speed to zero) is prolonged. Since the impulsive force
= Distance / Time , the force will decrease when the time increase.
b) This will decrease the impulsive force on the passengers and the driver.
3. The seats of the passengers are strengthened to protect the passengers.
4. Safety belts:
a) Passengers have to fasten the safety belts. When the car stops suddenly, the inertia of the passengers will result in the passengers being flung to the front and hitting the windscreen of the car.
b) Hence, safety belts will slow down the motion of the passengers.
5. Airbags are built in some cars. When an accident happens, the airbags will be filled with air. This will prolong the time of action and reduce the impulsive force on the passenger.

Ways to utilize impulsive force

Material arts player break a few pieces of bricks
- A martial arts player ia able to break a pile of bricks with ease.
- This is because the hand of the player moves very fast and stops when it hits the top brick.
- Hence, the time of contact of the hand with the brick is short and this will increase the impulsive force on the bricks.
- The bricks are easily broken because of the big impulsive force.
The pestle and mortar
- The pestle and mortar are made of hard materials.
- During pounding or grinding, the pestle moves very fast. The mortar stops the motion of the pestle in a short time.
- A strong impulsive force is produced and the food can be broken into pieces easily.
The pile and the pile driver
- A pile driver is made of hard steel alloy.
- The pile driver is released very fast hit the hard pile.
- The time taken to hit the pile is short because both surfaces are hard.
- Hence, a big impulsive force is produced on the pile and it will be driven into the ground to support the foundation of the structure of a tall building.

Analysing Forces in Equilibrium

Vector Addition of Forces

1. A resultant force is a single force that represents the combined effect of two or more
  forces in magnitude and direction. The direction of the forces have to be taken into
  consideration when forces are added.

2. If the forces act in the same straight line, the resultant is found by simple addition or
  subtraction as shown in figure 2.1

  Resultant force, F = F1 – F2

  Figure 2.1

3. The resultant of forces that do not act in the same straight line can be determined by
  using the parallelogram law.


4. The parallelogram law states that if two forces acting at a point are represented in size
  and direction by the sides of a parallelogram drawn from the point, their resultant is
  represented in size and direction by the diagonal of the parallelogram drawn from the
  point.

Forces in Equilibrium

1. An object is said to be in equilibrium if the object is at rest or is moving with a constant velocity in a straight line.

2. The resultant force that acts on an object is zero if it is in equilibrium. In other words, the forces that act on the object are balanced in all directions.

3. If object is in equilibrium, the resultant force that acts is zero.

4. For two forces acting in the same direction or opposite direction, if the force is not zero, then the object is not in equilibrium.

Elasticity

Understanding Elasticity

Elasticity is the ability of a material to return to its original shape and size when the external force acting on it is removed.

It is due to the strong intermolecular forces between the molecules of the solid.
(you have to be able to explain elasticity in terms of intermolecular forces)

Hooke’s Law States that the extension of a spring is directly proportional to the applied force provided that the elastic limit is not exceeded.

Elastic limit of a spring is the maximum force that can be applied to a spring such that the spring will be able to be restored to its original length when the force is removed.

If the elastic limit is exceeded, the length of the spring is longer than the original length even though the force no longer acts on it. It is said to have permanent extension.

Hooke's law Graph

Force Vs Extension

k = force constant of the spring (equal of the gradient of the graph)

x = extension

Force constant is the force that is required to produce one unit of extension of the spring.It is the measure of the stiffness of the spring.

The curve at the end occurs represents the moment before the material breaks.

Factors influencing the elasticity of a spring:
a. Type of spring material
b. diameter of the coil of spring
c. diameter of the wire of spring

d. arrangement of the spring.

Point 1 is the Limit of Proportionality. Point 2 is the Elastic Limit. Point 3 is the Yield Point.

Before the limit of proportionality, the material obeys Hooke’s Law. After it, Force is no longer proportional to extension, and the graph begins to curve.

The Elastic Limit is the point when a material stops behaving elastically, and starts behaving plastically. The area before this point is called the elastic region; after it, the plastic region.

The Yield Point is the point where the material starts to stretch without applying any additional force.

Elastic Potential Energy, U

Elastic potential energy is the energy transferred to the spring when work is done on the spring.

k = force constant

x = spring extension

Work and Energy

 Work

1. Everyday we move or certain object to do work.
2. work is done when a force is exerted to move an object through a distance in the direction of the force.
3. Work W is defined as product of the force and the displacement of an object in the direction of the force.
Work=Fs
  Where,

F= the force acting
S= the displacement (or distance traveled in the direction of the force)

4 .Work is a scalar quantity and its unit is joule (J) or N m. 1 joule =1nm
 Example:
  A block which is at rest is acted on by force of magnitude 3 N in different direction. Determine the wok done by the block in each case.
  a) The force act from the left, the object move to the right for 2 m.
  b) The force act from the right, the object to the left for 2 m.


Solution

a) F=3 N b) F= -3 N
moving to the right for 2 m moving to the left for2 m (negative
Work done,W= Fs sign indicates object move to the left)
  =3 N x (-2 m) Work done W = Fs
  =6 Nm = -3 N x (-2m)
  =6 Nm


5 .1 joule is the work done when a force of 1newton moves of an object for 1 m in the direction of the force .
6 .Work is not done when a force is exerted on an object but the object does not move.
7 .In short, work is not done :

a) The direction of motion is perpendicular to the direction of the force exerted
b) Force is exerted on the object but the object does not move.



Energy


1. We need energy to do work.
2. Energy is defined as the Potential or the ability to do work.
3. Energy is scalar quantity and its unit is the joule (J) or N m.
4. Energy can exist in various form. Examples potential energy, kinetic energy, heat energy, electrical energy and sound energy.
5. Energy cannot be created or destroyed. The work done related to the change of the form of the energy.
Example
  A student of mass 50 kg walks up a flight of stairs 1.5 m high. What is…

a) the work done by the student?
Work = Fx s
  =mg x s
  =(50 x 10) N x 1.5 m
  =750 J
b) energy needed = work done
  =750 J

Power, Energy and Efficiency

POWER

1. The power,P, is the rate at which work is done or the rate of change of energy.
 
  Power, P = Work done ,W / Time taken , T

  Or
 
  Power, P =   Change of energy /  Time taken , T

2. The SI unit of power is watt (w).
3. 1 watt is defined as the power required to perform 1 joule of work in 1 second.
4. Power depends on the time taken and the work done .
5. People or engine with high power rating can get the work done in short time.
6. For a force F which produces a constant velocity, V,or a stationary object , the power generated is:
  P= Fv
  Proof:
 
  Power=  Work /  Time
  = (Force x Displacement) /  Time

  =Force x ( Displacement/  Time)
  = Force x velocity
 P= Fv

POTENTIAL ENERGY
1. Potential energy is the energy possessed by an object due to its position or state.
2. Potential energy can be classified into gravitational potential energy and elastic potential energy.


GRAVITATIONAL POTENTIAL ENERGY

The gravitational potential energy of an object depends on:
a) its mass
b) its height
c) the gravitational field


RELATIONSHIP BETWEEN WORK AND GRAVITATIONAL POTENTIAL ENERGY


The work done against the force of gravity is known as the gravitational potential energy

Gravitational potential energy= mgh
Where, m= mass
  g= Acceleration due to gravity
  h= Change in the height of the object

ELASTIC POTENTIAL ENERGY

1.Energy is needed to compress and extend an elastic material such as a spring and rubber.
2.The spring obtains its energy when work is done on it by compressing or stretching it.
3. The energy which an object possesses when it is compressed or stretched is known as the elastic potential energy .

RELATIONSHIP BETWEEN WORK AND ELASTIC POTENTIAL ENERGY

Work done = mean force x displacement
  W= 1/2 fx
 
• The extension of spring will increase if the force applied increases.
• Therefore, the elastic potential energy stored in the spring.
=Work done
= 1 / 2 Fx





KINETIC ENERGY


1. Kinetic energy is the energy possessed by an object due to its motion.
2. The kinetic energy of a moving object depends on its mass and speed.
Kinetic Energy= 1/2 mv^2   = (one over two multiply mass multiply velocity squared)


Where m is the mass of an object, v is speed of the object.


RELATIONSHIP BETWEEN WORK AND KINETIC ENERGY

1. Newton’s first Law of motion states that an object that moves with constant velocity will continue to move at this velocity if no external force acts on the object.
2. That mean an object which moves with constant velocity will conserve its kinetic energy.
3. Work is done when the kinetic energy increases or decreases. The change in kinetic energy of an object is equal to the work done on that object.
4. W= change in kinetic energy
  = 1/2 (mv^2- mu^2)



 PRINCIPLE OF CONSERVATION OF ENERGY

 The principle of conservation of energy states that energy can neither be destroyed nor created but it can change from one form to another.
 The changes of kinetic energy to gravitational potential energy also proves the equation of kinetic energy, v = u -2gh


EFFICIENCY

The efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy.
 
Efficiency =( Useful energy output / energy input) x100 %


 EFFICIENCY OF MACHINES

1.Machines are devices that make our work easier.
2.Machines require energy to work. This energy is called the input.
3.Machines transforms this input into other forms of energy to perform useful works.
4.However, the useful work obtained is not equal to the input as there is energy “loss” In this process. This loss is mainly due to work done against frictional forces and takes the forms of heat.
5.So, a machines is not perfect because the work done by the effort or input energy is not wholly used to overcome the load.

Work

Understanding Work, Energy, Power and Efficiency Physics form


Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x S
3. W= work done, F = force applied, S = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm


5. Work is not done when:
a. The object is stationary aka not moving
b. No force is applied on the object in the direction of displacement.
c. The direction of motion of the object is perpendicular to that of the applied force.
6. When work is done to an object, energy is transferred to the object.


Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:
a. ½ Mv²
b. M = mass, v = velocity
c. Unit: Joule /

kgm²s^-2

6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.
a. E = mgh
b. M = mass, g = acceleration due to gravity, h = height in metre


Conservation of energy
1. The principle of conservation of energy states that energy cannot be created or destroyed but can change from one form to another form of energy.
2. Total amount of energy remains the same.
3. When water falls from a dam, its potential energy changes to kinetic energy.
4. When a swing moves from one position to another position, its potential energy changes to kinetic energy alternately.


Power
1. Power is defined as the rate of doing work.


a. Power = (Work / Time)


b. P = power, W = work, T = time


2. SI unit for work is = watt (W).


Efficiency


1. Efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy.


2. Efficiency = (useful Energy output / Energy input ) X 100%


a. Efficiency = (Useful power output / Power input) X 100%


b. Unit is given in percentage.


You must know the importance of maximising the efficiency of device.

Understanding Physics

Of Course there will be no SPM question that ask you : What is Physics?

But in the case somebody ask you..answer with this:

Physics is the study of natural phenomena and the properties of matter.

There are many fields of study in physics, BUT in SPM you will only be assesed in these topics.

1. Force and Motion.
2. Heat.
3. Light.
4. Waves.
5. Electricity and Electromagnetism.
6. Electronics.
7. Nuclear Physics.

Understanding Derived and Base Quantities

Understanding Derived and Base Quantities

Physical quantities are quantities that can be measured. e.g. Length, Temperature, Speed, Time.

Quantities or qualities that cannot be measured are not physical quantities. e.g. happiness, sadness etc.

Physical quantities can be divided into Base quantitied and Derived quantities.

(i) Physical quantities are quantities that can be measured or can be calculated.
(ii) The base quantities are “building block” quantities from which other quantities are derived from.
(iii) The base quantities and their S.I. units are:

• Base quantities S.I. units
• Mass kg
• Length m
• Time s
• Electric current A
• Thermodynamic
• temperature K

(iii) Derived quantities are quantities derived (iv) Examples of derived quantities.

• Derived quantities S.I. units
• area m2
• density kg m-3
• weight N
• velocity m s-1

Standard Notation: To express very large or very small numbers.
Example; A X 10 n (ten to the power of n), n must be an integer and 1 ≤ A <10

Understanding Scalar and Vector Quantities

Scalar quantities: Quantities that have magnitude only. ( Speed, mass, distance)

Example:

For example speed has unit of ms^-1. but it has no direction.

Mass is kg but we don't know the direction.

Distance is 2km but no direction.

Vector quantities: Quantities that have magnitude and direction. (Velocity, Weight, Displacement)

Example:

Velocity unit is ms^-1 but we must state the direction that is whether from right to left.

Weight unit is Kg but the direction is towards the gravity pull of the earth.

Displacement is 2km but to the north from the point of reference.

Understanding Measurements

A micro balance is used to measure minute masses. It is sensitive but not very accurate.


Slide callipers are usually used to measure the internal or external diameter of an object.


A micrometer screw gauge is used to measure the diameter of a wire of the thickness of a thin object.

All measurement must consider this:

Accuracy: Ability of the instrument to measure the true value or close to the true value. The smaller the percentage error, the more accurate the instrument is.

Sensitivity of an instrument is the ability of the instrument to detect any small change in a measurement.

Consistency: ability of the instrument to produce consistent measurement.(the values are near to each other). The lower the relative deviation, the more consistent the measurement is.

How to increase accuracy?
- repeat the measurements and get the mean value.
- correcting for zero error.
- avoiding parallax error.
- use magnifying glass to aid in reading.

The sensitivity of a mecury thermometer can be increased by;
-having a bulb of thinner wall.
-having a capillary tube of smaller diameter or bore.

Analysing scientific investigation

A variable is a quantity that can vary in value.

Manipulated variable is a variable that is set or fixed before and experiment is carried out. it is usually plotted on x- axis.

Responding variable is a variable that changes according to and dependent to manipulated variable. it is usually plotted on y-axis.

Fixed variable is fixed and unchanged throughout the experiment.

Inference: state the relationship between two VISIBLE QUANTITIES in a diagram or picture.

Hypothesis: state the relation ship between two MEASURABLE VARIABLES that can be investigated in a lab.

How to tabulate data?

-the name or the symbols of the variables must be labelled with respective units.
-all measurements must be consistent with the sensitivity of the instruments used.
-all the calculated values must be correct.
-all the values must be consistent to the same number of decimal places.

A graph is cosidered well-plotted if it contains the following:
- a title to shoe the two variables and investigation.
- two axes labelled with correct variables and units
- scales must be chosen carefully and graph must occupy more than 50% of the graph paper.
-all the points are correctly drawn.
-the best line is drawn.

What is Physics?

What is Physics?

Physics is a branch of science which studies physical and natural phenomena around us.

Examples of natural phenomena are formation of rainbow, solar eclipse, the fall of things from up to down, the cause of sunset and sunrise, formation of shadow and many more.

Physics mostly answers whys rather than what and it gives scientific, systematic and consistent explanation based on the concepts of physics.

Physics knowledge will increase as the flow of time; new concepts will replace old concepts if proven to be accurate.

The word physics evolved from ‘physikos’ a Greek word for nature.

There are two main divisions of physics which are:
a. Classical physics: motion and energy, mechanics, force and motion, heat, sound, electricity, magnetism and light.
b. Modern physics: atomic, molecular and electron physics, nuclear physics, relativity, origin of universe, astrophysics.

Topics learnt in form 4 are:

1. Introduction to physics
2. Forces and motion
3. Forces and pressure
4. Heat
5. Light



Topics in form 5 would be:

1. Waves
2. Electricity
3. Electromagnetism
4. Electronics
5. Radioactivity

Several discoveries and contributions based on the knowledge of physics:

1911 –New Zealand-born British physicist Ernest Rutherford (UK, New Zealand), proposed that an atom has a positively charged nucleus called Proton.
1957 –Sputnik I, first satellite to orbit the earth (Soviet Union).
1969 –Man landed on the moon – Neil Armstrong became the first human being to set foot on the moon (US).
1989 –www was launched by British Engineer Tim Berners-Lee and his colleague (UK).
1990 –The Hubble Space Telescope was built and launched into orbit by NASA (US).

Among the important figures in Physics:
Galileo Galilei
Isaac Newton
Charles Augustin de Coulomb
Albert Einstein
Stephen William Hawking

Study of Physics

1. As the other branches of science, scientific skills is necessary in the process of undertaking research and analysis in physics.

2. Research or Experiments are done systematically and step by step based on scientific method.

3. Scientific method

Identifying Problem ---- Making Hypothesis -----Planning investigation ------Identifying and controlling variables ----conducting experiment ----collecting data ----recording data----making conclusions---writing reports.


Careers in Physics included (examples)
1. Engineering
2. Computer Science
3. Industry
4. Communication
5. Electronics
6. Medicine – X ray
7. Environmental Science
8. Basic Research

Constructing a new fundamental physics

A Feynman diagram of arenormalized vertex in quantum electrodynamics

As the philosophically inclined continued to debate the fundamental nature of the universe, quantum theories continued to be produced, beginning with Paul Dirac’s formulation of a relativistic quantum theory in 1928. However, attempts to quantize electromagnetic theory entirely were stymied throughout the 1930s by theoretical formulations yielding infinite energies. This situation was not considered adequately resolved until after World War IIended, when Julian Schwinger, Richard Feynman, and Sin-Itiro Tomonaga independently posited the technique of renormalization, which allowed for an establishment of a robust quantum electrodynamics (Q.E.D.).[38]

Meanwhile, new theories of fundamental particles proliferated with the rise of the idea of the quantization of fields through “exchange forces” regulated by an exchange of short-lived “virtual” particles, which were allowed to exist according to the laws governing the uncertainties inherent in the quantum world. Notably,Hideki Yukawa proposed that the positive charges of the nucleus were kept together courtesy of a powerful but short-range force mediated by a particle intermediate in mass between the size of an electron and a proton. This particle, called the “pion”, was identified in 1947, but it was part of a slew of particle discoveries beginning with the neutron, the positron (a positively charged antimatter version of the electron), and the muon (a heavier relative to the electron) in the 1930s, and continuing after the war with a wide variety of other particles detected in various kinds of apparatus: cloud chambers, nuclear emulsions, bubble chambers, and coincidence counters. At first these particles were found primarily by the ionized trails left by cosmic rays, but were increasingly produced in newer and more powerful particle accelerators.[39]

Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. The experiment is done in order to investigate the properties of aquark gluon plasma such as the one thought to exist in the ultrahot first few microseconds after the big bang.

The interaction of these particles by scattering and decay provided a key to new fundamental quantum theories. Murray Gell-Mann and Yuval Ne'eman brought some order to these new particles by classifying them according to certain qualities, beginning with what Gell-Mann referred to as the “Eightfold Way”, but proceeding into several different “octets” and “decuplets” which could predict new particles, most famously the Ω−, which was detected at Brookhaven National Laboratory in 1964, and which gave rise to the “quark” model of hadron composition. While thequark model at first seemed inadequate to describe strong nuclear forces, allowing the temporary rise of competing theories such as the S-Matrix, the establishment of quantum chromodynamics in the 1970s finalized a set of fundamental and exchange particles, which allowed for the establishment of a “standard model” based on the mathematics of gauge invariance, which successfully described all forces except for gravity, and which remains generally accepted within the domain to which it is designed to be applied.[37]

The Standard Model groups the electroweak interaction theory and quantum chromodynamics into a structure denoted by the gauge groupSU(3)×SU(2)×U(1). The formulation of the unification of the electromagnetic and weak interactions in the standard model is due to Abdus Salam, Steven Weinberg and, subsequently, Sheldon Glashow. After the discovery, made at CERN, of the existence of neutral weak currents,[40][41][42][43] mediated by the Z boson foreseen in the standard model, the physicists Salam, Glashow and Weinberg received the 1979 Nobel Prize in Physics for their electroweak theory.[44]

While accelerators have confirmed most aspects of the Standard Model by detecting expected particle interactions at various collision energies, no theory reconciling the general theory of relativity with the Standard Model has yet been found, although string theory has provided one promising avenue forward. Since the 1970s, fundamental particle physics has provided insights into early universe cosmology, particularly thebig bang theory proposed as a consequence of Einstein’s general theory. However, starting from the 1990s, astronomical observations have also provided new challenges, such as the need for new explanations of galactic stability (the problem of dark matter), and accelerating expansion of the universe (the problem of dark energy).

The radical years: general relativity and quantum mechanics

The gradual acceptance of Einstein’s theories of relativity and the quantized nature of light transmission, and of Niels Bohr’s model of the atom created as many problems as they solved, leading to a full-scale effort to reestablish physics on new fundamental principles. Expanding relativity to cases of accelerating reference frames (the “general theory of relativity”) in the 1910s, Einstein posited an equivalence between the inertial force of acceleration and the force of gravity, leading to the conclusion that space is curved and finite in size, and the prediction of such phenomena as gravitational lensing and the distortion of time in gravitational fields.
Further information: History of general relativity

Niels Bohr (1885–1962)

The quantized theory of the atom gave way to a full-scale quantum mechanics in the 1920s. The quantum theory (which previously relied in the “correspondence” at large scales between the quantized world of the atom and the continuities of the “classical” world) was accepted when the Compton Effect established that light carries momentum and can scatter off particles, and when Louis de Broglie asserted that matter can be seen as behaving as a wave in much the same way as electromagnetic waves behave like particles (wave-particle duality). New principles of a “quantum” rather than a “classical” mechanics, formulated in matrix-form by Werner Heisenberg,Max Born, and Pascual Jordan in 1925, were based on the probabilistic relationship between discrete “states” and denied the possibility of causality. Erwin Schrödingerestablished an equivalent theory based on waves in 1926; but Heisenberg’s 1927 “uncertainty principle” (indicating the impossibility of precisely and simultaneously measuring position and momentum) and the “Copenhagen interpretation” of quantum mechanics (named after Bohr’s home city) continued to deny the possibility of fundamental causality, though opponents such as Einstein would metaphorically assert that “God does not play dice with the universe”.[37] Also in the 1920s, Satyendra Nath Bose's work on photons and quantum mechanics provided the foundation for Bose-Einstein statistics, the theory of the Bose-Einstein condensate, and the discovery of the boson.
Further information: history of quantum mechanics

The emergence of a new physics circa 1900

Marie Skłodowska Curie(1867–1934)

The triumph of Maxwell’s theories was undermined by inadequacies that had already begun to appear. The Michelson-Morley experiment failed to detect a shift in thespeed of light, which would have been expected as the earth moved at different angles with respect to the ether. The possibility explored by Hendrik Lorentz, that the ether could compress matter, thereby rendering it undetectable, presented problems of its own as a compressed electron (detected in 1897 by British experimentalist J. J. Thomson) would prove unstable. Meanwhile, other experimenters began to detect unexpected forms of radiation: Wilhelm Röntgen caused a sensation with his discovery of x-rays in 1895; in 1896 Henri Becquerel discovered that certain kinds of matter emit radiation on their own accord. Marie and Pierre Curie coined the term “radioactivity” to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel’s forms of radiation with electrons and the element helium. In 1911 Rutherford established that the bulk of mass in atoms are concentrated in positively charged nuclei with orbiting electrons, which was a theoretically unstable configuration. Studies of radiation and radioactive decay continued to be a preeminent focus for physical and chemical research through the 1930s, when the discovery of nuclear fission opened the way to the practical exploitation of what came to be called “atomic” energy.

Albert Einstein (1879–1955)

Radical new physical theories also began to emerge in this same period. In 1905 Albert Einstein, then a Bern patent clerk, argued that the speed of light was a constant in all inertial reference frames and that electromagnetic laws should remain valid independent of reference frame—assertions which rendered the ether “superfluous” to physical theory, and that held that observations of time and length varied relative to how the observer was moving with respect to the object being measured (what came to be called the “special theory of relativity”). It also followed that mass and energy were interchangeable quantities according to the equation E=mc2. In another paper published the same year, Einstein asserted that electromagnetic radiation was transmitted in discrete quantities (“quanta”), according to a constant that the theoretical physicist Max Planck had posited in 1900 to arrive at an accurate theory for the distribution of blackbody radiation—an assumption that explained the strange properties of the photoelectric effect. The Danish physicist Niels Bohr used this same constant in 1913 to explain the stability of Rutherford’s atom as well as the frequencies of light emitted by hydrogen gas.
Further information: History of special relativity