Transcript FUNDAMENTALS OF PHYSICS

SYSTEMS of UNITS
&
RADIOLOGIC UNITS
SYSTEM OF UNITS
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SI
MKS
CGS
BRITISH
BASIC QUANTITIES
• LENGTH
• MASS
• TIME
SYSTEM OF UNITS
LENGTH
MASS
TIME
SI
MKS
CGS
BRITISH
METER
METER
CENTIMETER
FOOT
GRAM
POUND
SECOND
SECOND
KILOGRAM KILOGRAM
SECOND
SECOND
The International System of Units (abbreviated SI from
the French phrase, Système International d'Unités) is the
most widely used system of units. It is the most common
system for everyday commerce in the world, and is almost
universally used in the realm of science
Scientists, chiefly in France, had been advocating and
discussing a decimal system of measurement based
on natural units at least since 1640, but the first official
adoption of such a system was after the French
revolution of 1789. The metric system tried to choose
units which were non-arbitrary and practical, merging
well with the revolution's official ideology of "pure
reason"; it was proposed as a considerable
improvement over the inconsistent customary units
which existed before, whose value often depended on
the region
According to a survey taken many years ago, the only other
countries that have not officially adopted the metric system are
Liberia (in western Africa) and Myanmar (also known as Burma, in
Southeast Asia). These two countries did not have an official policy
of converting to metric, at least at the time of the survey. Despite
recent repeated inquiries to the governments of both Liberia and
Myanmar, no response from either country has been received as to
whether an official policy has been adopted since this survey was
conducted. Their Web sites utilize both inch-pound and metric units.
Visitors to these countries report some evidence of the use of the
metric system. Most other countries have either used the metric
system for many years, or have adopted the metric system within the
last 30 or 40 years. There is controversy about how to define
whether a country is metric. Metrication is a process that does not
happen all at once, but is rather a process that happens over time.
Although nearly every country has taken steps to replace traditional
measurements, the fact remains that among countries with nonmetric usage the U.S. is the only significant holdout.
SI UNITS
• LENGTH----METER (m)
• MASS-------KILOGRAM (kg)
• TIME--------SECOND (s)
1 METER
The most important unit is that of length: one metre was originally defined
to be equal to 1/10 000 000th of the distance from the pole to the equator
along the meridian through Paris. (Prior discussions had often suggested
the length of a seconds pendulum in some standard gravity, which would
have been only slightly shorter, and perhaps easier to determine.) This is
approximately 10% longer than one yard. Later on, a platinum rod with a
rigid, X-shaped cross section was produced to serve as the easy-to-check
standard for one metre's length. Due to the difficulty of actually measuring
the length of a meridian quadrant in the 18th century, the first platinum
prototype was short by 0.2 millimetres. More recently, the metre was
redefined as a certain multiple of a specific radiation wavelength, and
currently it is defined as the distance travelled by light in a vacuum in a
specific period of time. Attempts to relate an integer multiple of the metre to
any meridian have been abandoned
1m=100 cm=1000 mm
1cm=10mm
1m=100 cm
1m=100 x 10= 1000 mm
The original base unit of mass in the metric system
was the gram, chosen to match the mass of one
cubic centimetre of water. For practical reasons, the
reference standard that was deposited at the
Archives de la république on June 22, 1799 was a
kilogram (a cylinder of platinum). One kilogram is
about 2.2 pounds. In 1889, the first General
Conference on Weights and Measures (CGPM)
sanctioned a replacement prototype, a cylinder of a
90% platinum, 10% iridium alloy; this has served as
the standard ever since, and is stored in a Paris vault.
The kilogram became the base unit in 1901.
1 kg=1000 g ???
YES !
The metric unit of time became the second,
originally defined as 1/86 400th of a mean
solar day. The formal definition of the
second has been changed several times as
more accurate definitions became possible,
based first on astronomic observations,
then the tuning fork clock, quartz clock, and
today the caesium atomic clock
TIME
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1 MINUTE =60 SEC.
1 DAY =24 HOURS
1 DAY = _____MINUTES
1DAY = _____SECONDS
MKS SYSTEM
• Length---METER (m)
• Mass-----Kilogram (kg)
• Time-----Second (s)
CGS system
• Length---centimeter (m)
• Mass-----gram (g)
• Time-----Second (s)
derived units
Derived quantity
SI
derived
Name
unit
Symbol
area
square meter
m2
volume
cubic meter
m3
speed, velocity
meter per second
m/s
acceleration
meter per second squared
m/s2
wave number
reciprocal meter
m-1
mass density
kilogram per cubic meter
kg/m3
specific volume
cubic meter per kilogram
m3/kg
current density
ampere per square meter
A/m2
magnetic field strength
ampere per meter
A/m
amount-of-substance
concentration
mole per cubic meter
mol/m3
luminance
candela per square meter
cd/m2
mass fraction
kilogram per kilogram, which
may be represented by the
number 1
kg/kg = 1
BRITISH SYSTEM OF UNITS
British system
• Length---Foot (ft)
• Mass-----Pound (lb)
• Time-----Second (s)
METRIC
BRITISH
CONVERSION
yard = 0.9144 metres - same in US
1 pound = 0.453 592 37 kilograms - same
in US
1 gallon = 4.546 09 litres - different in US
RADIOLOGIC QUANTITIES SI
UNITS
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EXPOSURE ---AIR KERMA (Gya)
ABSORBED DOSE---GRAY (Gyt)
EFFECTIVE DOSE---SEIVERT (Sv)
RADIOACTIVITY---BECQUEREL (Bq)
RADIOLOGIC QUANTITIES
CUSTOMARY UNITS
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EXPOSURE ---Roentgen (R)
ABSORBED DOSE---rad (rad)
EFFECTIVE DOSE---rem (rem)
RADIOACTIVITY---curie
EXPOSURE ( INTENSITY)
The roentgen (R) is a measure of radiation intensity
of x rays or gamma rays. It is formally defined as
the radiation intensity required to produce and
ionization charge of 0.000258 coulombs per
kilogram of air. It is one of the standard units for
radiation dosimetry, but is not applicable to alpha,
beta, or other particle emission and does not
accurately predict the tissue effects of gamma rays
of extremely high energies. The roentgen has
mainly been used for calibration of x-ray
machines..
1R=2.58 x
-4
10 C/kg
1 AIR KERMA=100R
ABSORBED DOSE
The rad is a unit of absorbed radiation
dose in terms of the energy actually
deposited in in any kind of matter,
including tissue. The rad is defined as an
absorbed dose of 0.01 joules of energy per
kilogram of tissue.
This applies to any kind of radiation:
x-rays, gamma rays, beta rays, etc.
rad= RADIATION
ABSORBED DOSE
1 Gray=100 rad
EFFECTIVE DOSE
The biologically effective dose in rems is the radiation
dose in rads multiplied by a "quality factor" which is an
assessment of the effectiveness of that particular type
and energy of radiation. For alpha particles the relative
biological effectiveness (rbe) may be as high as 20, so
that one rad is equivalent to 20 rems. However, for xrays and gamma rays, the rbe is taken as one so that the
rad and rem are equivalent for those radiation sources.
1 Sv = 100 rem
The SI derived unit of activity,
usually meaning radioactivity.
"Radioactivity" is caused when
atoms disintegrate, ejecting
energetic particles
RADIOACTIVITY
The curie (Ci) is the old standard
unit for measuring the activity of a
given radioactive sample. It is
equivalent to the activity of 1 gram
of radium. It is formally defined by:
1 curie = amount of material that
will produce 3.7 x 1010 nuclear
decays per second.
1 becquerel = amount of material
which will produce 1 nuclear decay
per second.
1 curie = 3.7 x 1010 becquerels