Showing posts with label motion. Show all posts
Showing posts with label motion. Show all posts


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The moon is Earth's only natural satellite. The moon is a cold, dry sphere whose surface is studded with craters and strewn with rocks and dust (called regolith). The moon has no atmosphere. The moon is about 238,900 miles (384,000 km) from Earth on average. The moon's diameter is 2,159 miles (3,474 km), 27% of the diameter of the Earth. The moon's mass is (7.35 x 10 22 kg), about 1/81 of the Earth's mass. The moon's gravitational force is only 17% of the Earth's gravity. The moon's density is 3340 kg/m 3. This is about 3/5 the density of the Earth. 

Moseley’s Law

The frequency of a spectral line in characteristic X-ray spectrum varies directly as square of atomic number ‘Z’ of the element emitting it.

Moseley’s Law for X-rays

The frequency of a spectral line in characteristic X-ray spectrum varies directly as square of atomic number Z of element emitting it.

Mosley’s Experiment

Mosley in 1913 carried out a systematic study of Kα X-rays produced by elements from aluminum to gold using Bragg technique of X-rays scattering from a crystalline lattice of a potassium ferro-cyanide crystal. The characteristic Kα X-rays were produced by bombardment of targets with energetic electrons. The results of Mosley’s experiments confirmed the Bohr’s atomic theory. 

Mossbauer Effect

Rudolf Mossbauer, in 1958, discovered the recoil-free emission and absorption of gamma rays by nuclei. The Mossbauer effect states that when some atoms are held tightly in crystalline atomic structures, the gamma radiation emitted by their nuclei are very close to being recoil-free.  This implies that the emitted photon has the exact frequency that corresponds to the transition energy between the nuclear ground state and the excited state.  When this photon carrying the full nuclear transition energy strikes another similar nucleus also embedded in a tight crystalline structure, absorption may occur.  Because the nuclear energy levels are very sharply defined, only such a photon - one that carries the exact transition energy - may excite another nucleus. Because of the very narrowly defined nuclear energy states, the smallest change in the energy of the photon will destroy the resonance.  Thanks to this extreme sensitivity, Mossbauer spectroscopy has proven itself an excellent method to measure otherwise impossible to detect nuclear energy differences.  Minuscule energy variations, magnetic fields at the nucleus, and even distortions or asymmetries in the shape of the lattice that encloses the atom are enough to produce shifts and split tings in the absorption line.  All these alterations of the nuclear environment that produce an observable effect are called the nuclear hyperfine interactions.  

Most Probable Speed

It is the speed possessed by maximum number of molecules in a gas sample.


Change in position of an object with respect to time seen by an observer from a frame of reference.

Multiwire Drift Chamber

A multiwire drift chamber is a tracking device that was built to track particles in high energy physics collisions. It uses the timing information to determine the position of an ionizing particle. In a drift chamber the cathode is made up of either closely spaced wires or strips that are kept at distributed potentials. The advantage of this design is that the electrons produced by the incident radiation are directed towards the nearest anode wire with a constant drift velocity. The incident radiation produces electron ion pairs inside the active volume that drift towards the nearest anode and cathode. After passing through the chamber, the radiation is detected by a fast detector, such as scintillation counter, which produces a pulse. This pulse initiates a logic-enable pulse that starts a timing counter. The counter keeps on counting until it gets a stop signal that is generated when the electrons eventually reach the anode, produce avalanche, and produce an anode pulse. The number of ticks of the counter determines the time it has taken the electrons to reach the anode wire. Now, if the drift velocity of the electrons in the chamber gas is known, one can determine the distance traveled by the electron and hence position at which the electron was produced by the radiation.


It is an elementary particle, a lepton having spin ½ and about 200 times the mass of electron. It is usually formed from decay of Pion.  

Muonic Atom

It is an atom in which an electron is replaced by a negative muon orbiting close to or within the nucleus. Muonic atom consisting of a proton and negative with a reduced mass of 186 Me.   

Muonium (Mu)

It is a light, Hydrogen like neutral atom consisting of a positive muon μ+ and an orbital electron. Chemists consider Muonium to be a light unstable isotope of Hydrogen. It is formed when an energetic positive Muon slows down in an absorber and attracts an electron which then revolves about Muon. The reduced mass of Muon is within 0.5% of electron mass.

Musical Interval

The ratio of frequencies of two tones is called musical interval.

Musical Scale

If several tones in increasing order of their frequencies are arranged in a series such that they have a definite musical interval and their resultant effect is pleasant to the ear, it is called the musical scale.

Mutual Induction

When two coils are placed near each other such that the current flowing in one changes, emf is induced in the second coil. Such phenomenon is known as mutual induction. 


Term used for short sight. Light from a distant object forms an image before it reaches retina. A myopic person has clear vision when looking objects close to them but distant objects will appear blurred. 

Principles of Special Theory of Light

1. Does the speed of light depend on motion of source of light?

No, the motion of light is not affected by motion of source of light.

2. Is photon a particle?

The photon is a particle of light, but it doesn’t possess all essential properties we ascribe to a tiny ball i.e. photon doesn’t behave as a common sense particle but it has got some peculiar properties.

3. When we follow Albert Einstein in developing special theory of relatively, we are developing a theory of space and time.

4.  The principles of special theory of light.

Principle 1:

Colloquial statement: If we are in unaccelerated vehicle, its motion has no effect on the way things happen inside it.

Formal statement: The laws of physics are the same in all unaccelerated reference frames.
Principle 2: The motion of light is not affected by motion of source of light.

5. The special theory of relativity
          Special: The word special in name arises because we employ only unaccelerated reference frames, not all reference frames that one can think of. In other words, we special to the way things appear when observed from uniformly moving reference frames.
          Relativity:-The word relativity comes from a phrase coined by Henri Poincare, an eminent French physicist and mathematician.
In 1904, Poincare was invited to address the international congress of arts and science, held in st Louis to commemorate the 100th anniversary of Louisiana Purchase. Poincare spoke of a principle of relativity.
If you are in plane on its way from Chicago to phoenix, another plane making the return flight, over wheat fields of Kansas. A farmer, looking up, notes that you are flying south west at 500 miles/hr relative to his wheat fields.
The pilot of return flight notes that the distance between the two planes is decreasing at about 1000 miles/hr. So far as the pilot is concerned, you are travelling at about 1000 miles/hr relative to his plane.
The essence is this:  statements about uniform motion relative to a specified reference frame wheat fields or another air plane are meaningful.
A quantitative statement about uniform motion without specification of a reference frame is not meaningful. Why? Because our principle 1 says we cannot discern uniform motion without recourse to some reference frame.
Take first the colloquial form of that principle if we are in an unaccelerated vehicle, its motion has no effect on the way things happen inside it. So by just doing experiments inside the vehicles, we have no way to assign a velocity to the vehicle. Only if we look out of window and thereby use wheat fields of Kansas as an outside reference frame. We can decide on velocity (velocity to that outside reference frame).
          Theory: It appears because principles 1 & 2 are generations from observation and experiment.

  •  Observes in all un accelerated reference frames measure the same speed for light ( in vacuum) from any given source.
  • They all measure 3*10 8m/sec   always for light in vacuum.
  • This remarkable property is called “constancy of speed of light”.
Note:-Some factors other than light may be observed differently in unaccelerated frames.

7.  An “event” is anything that happens at some definite locations at some definite time. Proto typical examples are your birth, assassination of Abraham Lincoln etc. In contrast, a forest fire that sweeps across 10000 acres in 5 days does not constitute an “event” because the fire is spread out in space and time.
The adjective “definite” means   “distinct” or  “limited” for any one observing the happening.

  •  Spatially separated events that are simultaneous in one frame are, in general, not simultaneous when viewed from other reference frame.
  •  Simultaneity is a relative concept, but not an absolute one.
  • The concept of simultaneity between two events in different space points has an exact meaning only in relation to a given inertial system i.e.   “Each frame of reference has its own particular time”.
  • To measure the length of an object means to locate its end points simultaneously. As simultaneity    depends on frame of reference, the length measurements will also depend on frame of reference.
  • Thus, “The length i.e.  Space is a relative concept, not an absolute one”.
  • Thus there is no such thing as an absolute, global “now”.