A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Moon
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.
Motion
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.
Muon
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.
Myopia
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.
