## July 19, 2012

### Physics : CH # 2

Meter:
Meter is the unit of length in S.I. System.
Meter is defined as "The distance between the two marks on a Platinum-Iridium bar kept at 0OC in the   International Bureau of Weight and Measures in Paris."
One meter = 100 cm
One meter = 1000 mm

Kilogram:
Kilogram is the unit of mass in S.I. System.
"Kilogram is defined as the mass of a platinum cylinder placed in the International Bureau of Weight and   Measures in Paris."
One kilogram = 1000gram

Second:
Second is the unit of time in S.I. System.
A second is defined in terms of the time period of Cs-133 atoms.
i.e." one second is equal to 9,192,631,770 periods of vibrations of Cs-133 atoms."
60 seconds = one minute
3600 seconds = one hour

Fundamental Units:
The international system of units is based on seven independent units known as Fundamental or Basic Units. These are given here:

Derived Units:

The units that require two or more basic measurements of same units or different fundamental units for its definition are called derived units.

Error:
An error is defined as
"The difference between the measured value and actual value."
If two persons use the same instrument for measurement for finding the same measurement, it is not   essential that they may get the same results. There may arises a difference between their measurements. This difference is referred to as an "ERROR".

Types Of Error:

Errors can be divided into three categories:
(1) Personal Error
(2) Systematic Error
(3) Random Error

Personal Error:
An error comes into play because of faulty procedure adopted by by the observer is called "PERSONAL   ERROR".
Personal error comes into existence due to making an error in reading a scale. It is due to faulty   procedure adopted by the person making measurement.

Systematic Error:
The type of error arises due to defect in the measuring device is known as "SYSTEMATIC ERROR".
Generally it is called "ZERO ERROR". it may be positive or negative error. Systematic error can be   removed by correcting measurement device.

Random Error:
The error produced due to sudden change in experimental conditions is called "RANDOM ERROR".
For example:
Sudden change in temperature, change in humidity, fluctuation in potential difference (voltage).
It is an accidental error and is beyond the control of the person making measurement.