Archive | August, 2012

Mechanics AS

22 Aug

English: motion of the projectile

English: motion of the projectile (Photo credit: Wikipedia)

English: Projectile motion

English: Projectile motion (Photo credit: Wikipedia)

Three dimensional Cartesian coordinate system ...

Three dimensional Cartesian coordinate system with the x-axis pointing towards the observer (Photo credit: Wikipedia)

The addition of two vectors a and b

The addition of two vectors a and b (Photo credit: Wikipedia)

coordinate_system

coordinate_system (Photo credit: williamcromar)

The analysis of projectile motion is a part of...

The analysis of projectile motion is a part of classical mechanics. (Photo credit: Wikipedia)

Unit 1 Topic 1 Mechanics

Target sheet

I can:

1.  Equation of uniformly accelerated motion.

2. Displacement time graph

3. Velocity time graph.

4. Projectile Motion.

5. Principle of Conservation of Energy.

6. Vectors and Scalars.

7. Vector addition

8. Resolving a vector onto X-axis and Y-axis.

9. Air resistance and solid friction.

10. Static and Kinetic Equilibrium.

11. Coplanar forces.

12. Three Dimensional Forces.

Electric and Magnetic Fields.

22 Aug
English: Field of a positive and a negative po...

English: Field of a positive and a negative point charge. Thumbnail version (Photo credit: Wikipedia)

Charged particle drifts in a homogeneous magne...

English: Fleming's left hand rule shows the di...

English: Fleming’s left hand rule shows the direction of the thrust on a conductor carrying a current in a magnetic field. (Photo credit: Wikipedia)

Statement Spec ref Comments
explain what is meant by an   electric field and recognise and use the expression electric field strength E   = F/Q

83

draw and interpret diagrams using   lines of force to describe radial and uniform electric fields qualitatively

84

use the expression F = kQ1Q2/r2,   where k = 1/4πε0 and derive and use the expression E = kQ/r2   for the electric field due to a point charge

85

investigate and recall that   applying a potential difference to two parallel plates produces a uniform   electric field in the central region between them, and recognise and use the   expression E = V/d

86

investigate and use the   expression C = Q/V

87

recognise and use the expression W   = ½ QV for the energy stored by a capacitor, derive the expression   from the area under a graph of potential difference against charge stored,   and derive and use related expressions, for example, W = ½ CV2

88

investigate and recall that the   growth and decay curves for resistor–capacitor circuits are exponential, and   know the significance of the time constant RC

89

recognise and use the expression Q   = Q0 e−t/RCand derive and use   related expressions, for exponential discharge in RC circuits, for example, I   = I0e−t/RC

90

explore and use the terms   magnetic flux density B, flux Φ and flux linkage NΦ

91

investigate, recognise and use   the expression         F = BIl   sin θ and   apply Fleming’s left hand rule to currents

92

recognise and use the expression F   = Bqv sin θ and apply Fleming’s left hand rule to charges

93

investigate and explain   qualitatively the factors affecting the emf induced in a coil when there is   relative motion between the coil and a permanent magnet and when there is a   change of current in a primary coil linked with it

94

investigate, recognise and use   the expression ε = −d(NΦ)/dt   and explain how it is a consequence of Faraday’s and Lenz’s laws

95

The Cepheid Variable.

22 Aug
English: The oldest star of our Galaxy: HE 152...

English: The oldest star of our Galaxy: HE 1523-0901 (Photo credit: Wikipedia)

English: Diagram of how a common envelope is f...

Wireless Temperature Sensor Module uploading t...

Wireless Temperature Sensor Module uploading to emoncms via Nanode (Photo credit: Nathan Chantrell)

This ZAMS mass-luminosity table was generated ...

This ZAMS mass-luminosity table was generated using data from the isocrone calculation tool of Lionel Siess. The metallicity (Z) is 0.02 and the axis units use solar values. Note that the present-day Sun is more luminous than when it first joined the main sequence. (Photo credit: Wikipedia)

6. b) The graphs show the sensitivity of a particular brand photographic film and that of a charge coupled device, CCD, to different parts of the e.m spectrum.

The surface temperature of a star can be calculated once the wavelength of the peak of its spectrum (λmax) is known.  Use the graphs to explain why photographic film would be less suitable than CCDs for determining (λmax) for a star which radiates mainly in the visible region (400nm-700nm) of the e.m spectrum.

6b) (Answer.) The bandwidth of the film is from 350nm to 700nm whereas that of the CCD is from 300nm to 1000nm. The CCD is more suitable because the   relative sensitivity of the film is not uniform and ranges from 0.5 to a maximum of 1.0. The CCD is much better in this regard for it is uniform and close to 1 for the entire spectrum.

6c) State what happens to the hydrogen ‘burning’

6c) (Answer) The hydrogen fuses to become Helium and that is more stable.  When time will allow the star will be low in fuel and it will expand slightly.  This expansion causes the temperature to fall and the star becomes a red giant.

Why is a red giant more luminous than the main sequence star from which it originated, even though its temperature is lower?                      (1)

The luminosity depends upon the square of the radius and the 4th of the temperature.  The red giant expands more hence the radius factor plays a more important role than the temperature factor.

6d). Describe how observations of Cepheid variable stars are used to estimate the distance to nearby galaxies.

A longer time period for oscillation meant an intrinsically brighter star.  Astronomers then took this relationship and used it to determine the luminosity of variable stars at much greater distances.  From the luminosity, the distance to these stars can be determined using our expression for the radiant energy flux observed here on Earth.  Hence the estimate to the distance can be measured.

e)    Explain the meaning of the term binary system (1)

It is a star system which is made up of two stars having a common centre.

f)     At A C and E the light intensity  gets lower due to the fact that  shadow of one of the stars falling on the other.

g)    The dip at A is much smaller due to the fact that the other star is smaller. Whereas the dip at C is larger because the opposing star is larger.

h)   Estimate the orbital period of this binary.

From 2 hours to 24 hours or 22 hours.

Estimate the orbital period of this binary. (1)

i)     From B to D: 8 to 19 hours or 11 hours.

  1. Annual parallax method

tan θ = r/ d.

It is not a suitable method because it uses the parallax method hence it cannot be used for distant stars more than 650 ly.

  1. The two ways the white      dwarfs differ from the mainline stars are there is intense gravitational      pressure.  This makes it very small      in size.

Describe what happens to a star when it becomes a white dwarf?

Its strong gravitational field outweighs the fusion. And becomes very low luminous star,

  1.  40,0000K , 20,000K  10,000K, 5000K, 2500K

b) L = 1

lower left hand corner.

L= 104

They burn out quickly intense nuclear radiation.

  1.  The surface temperature could be same but      then again not for the colour is dependent upon the surface area and the      temperature.
  1. F = L/ A

Deneb has greater surface area. The luminosity is much larger,

  1.  Work it out your self.

The Nature of Particles

21 Aug
Radiation Scan

Radiation Scan (Photo credit: FastLizard4)

Classical physics (Rayleigh–Jeans law, black l...

Black body radiation for T=287K, which is the ...

Black body radiation for T=287K, which is the temperature of the earth. (Photo credit: Wikipedia)

English: Black body curves of Planck for vario...

English: Black body curves of Planck for various temperatures and comparison with classical theory of Rayleigh-Jeans. Italiano: Confronto fra le curve del corpo nero della teoria di Planck e della teoria classica di Rayleigh-Jeans. (Photo credit: Wikipedia)

The nature of particle.

1.Thomson concluded that those cathode rays were made up of particles.

2. Max Planck was trying to find out a model to understand the way in which a black body emits radiation.

3. Black body is perfect emitter and absorber of electromagnetic radiation.

4. He found that this was possible only if he had assumed radiations were emitted in packets.

5. Plank’s idea was not understood until Einstein, 1905 showed that black body radiation could be understood better if it was assumed that the radiation itself was quantised,  consisting of particle like packets of energy.

6.Each is referred to as photon.

Ultraviolet catastrophe:  Classical physics can predict that black body radiation based on long wavelength but not at short wavelengths, leading a disagreement that physicist calls as U.V catastrophe.

 

 Radiation Flux —Do the worked out example.

Light wave or particle?

21 Aug
No. Name   of Scientist Year   Place Perspective Key   ideas
1 Democritus B.C  Ancient Greece Particle theory “atoms  swarmed into the observer’s eyes”
2 Empedocles B.C Ancient Greece Wave theory “ Objects becomes visible   when touched by light rays emitted by the object”
3 Plato B.C Ancient Greece Wave theory
4 Leonardo Da Vinci 15th century Italy Wave theory “Compared the light   reflection to echo”
5 Francesco Maria Grimaldi 1665 Italy Wave theory “ Paper  published in 1665 after his death “ worked   on diffraction supporting  La Da Vinci
6 Robert Hooke  and Boyle 1665 England Wave theory “ Compared light with   water waves” explained the colours were formed on the water due to oil film
English: Validity of several theories for peri...

English: Validity of several theories for periodic water waves, according to Le Méhauté (1976). The light-blue area is the range of validity of cnoidal wave theory; light-yellow for Airy wave theory; and the dashed blue lines demarcate the required order of Stokes’ wave theory. The light-gray shading gives the range extension by numerical approximations using fifth-order stream-function theory, for high waves (H > ¼ H breaking ). (Photo credit: Wikipedia)

Light!  Wave or particle

In the end of seventeenth century saw a fierce debate about the nature of light.  Newton compared light with a stream of particles and this was accepted for reflection and refraction could be explained using this model.  He also argued that if light were waves then it would not form the sharp image of the object. (He did not realise that the light wave were too small!)

 

No. Name   of scientist Year Place Perspective Key   ideas
7  Thomas Young 1802 England Wave   theory His   double slit experiment
8 Leon   Foucault 1853 France Wave   theory His   experimental value of speed of light gave a death blow to particle theory for   it required the light to travel faster in H2O then in N2.
9 Albert   Einstein 1905 Germany Particle   theory Photo   electric effect.

The dilemma was recreated and then it was resolved only after Louis de Broglie produced his theory of wave-particle duality. He received the Nobel Prize for the world had accepted his explanation of light as being both particle and wave!

 

This new discovery gave rise to quantum mechanics.

 

 

10 Albert   Einstein 1905 Germany Particle   theory Photo   electric effect.
11 Thomson England Particle   theory Cathode   rays
12 Max   Plank 1918 Germany Quantised Radiation Black   Body Radiation
13 Louis   De Broglie 1927 France Issue resolved Crystals do show diffraction when   illuminated by electrons as confirmed independently by Davisson and Thomson.

The dilemma was recreated and then it was resolved only after Louis de Broglie produced his theory of wave-particle duality. He received the Nobel Prize for the world had accepted his explanation of light as being both particle and wave!

 

 

This new discovery gave rise to quantum mechanics.

 

 

 

 

 

 

T

 

 

 

 

Lights

Lights (Photo credit: cycloctopus)

Vectors and Scalars

8 Aug
UNIQUE PICTURE: Earth as seen from the outer S...

UNIQUE PICTURE: Earth as seen from the outer Solar System (Photo credit: Icarus Kuwait)

Weight is the force of attraction due to the Earth pulling us. This is due to gravity.  Fortunately, we do not go up.  The pull of the earth is always directed to the center of the earth.  Our mass , the total quantity of the matter in our body does not change, and there is no specific direction associated with this dimension.

Physical quantities that have both magnitude and direction are known as Vectors. Scalar quantity are those that only have magnitude and no directions.

Physics 101- Base Dimensions

6 Aug

Accordoing to Lord Kelvin, any thing we are able to measure is said to a Physical quantity.  There fore, standardistion was important.  Wempe   use the SI (System International) or the International System of Units in order to standardise our measurments. Thereby, assuring that a metre of cloth is of same lenght irrespective of time and place.

The Base dimensions in Physics are Lenght, Mass, Time and this is usually taught in grade 7 or 8, later the students learn about Current, Temperature . In chemistry they are taught about mole. Lastly, the sevent base dimension the Candela.

%d bloggers like this: