chapter 2:standards
classification of standards
- international standards
- primary standards
- secondary standards
- working standards
not available to ordinary user for purpose of day-to-day comparisons and calibration
primary standard
to calibrate @check & certify secondary reference standards
not easily available t an ordinary user of instruments for verification @calibration or working standards
secondary standards
s the maintanance & perriodic calibration of secondary standard against primary standards of the national standard lab@org.
freely available to the ordinary user of instrumentfor checking
working standards
high accuracy devices that commercially avasilable
standard of fundamental quantities
- mass
- time
- length
- tmperature
- absolute ampere
international prototype kiogram(platinum-iridium)
39mm height and 39mm diameter cylinder of the alloy
length
meter as a length of the international prototype meter,
the distance between two finely scribed lines of platinum iridium bar bar when subject to certain specified conditions
important!!!!!!!
"the meter is the length of the path traveled by light in vACUUM during a time interval of 1/299792458 of a second "
absolute ampere
unit of electric charge ,coulumb is define in term of the ampere one coulumb is the amount of electric charge carried in a current of one ampere flowing for one second
current then is the rate at which flows thruough a wire or surface.
the ampere is most accurately realised using watt balance, but is in practise maintained via ohms law from the unit of emf and resistance, the volt and ohm ,since the latter two can be tied to physical phenomena that are relatively easy te reproduce, the josephson junction and quantum hall effect respectively.
voltage standards
volt is defined as the potential different across a conductor when a current of one ampere dissipates one watt of power
volt is maintain internationally for practical measurement using the josephson effect
mari kite terjah !!!!!!
apo itu josephson effect??????
arrangement
two superconductor linked by a conducting barrier known as a josephson junction;the current that crosess the barrier is the josephson current.
- the junction is biased with dc current. the junction is exposed to high frequency microwave radiation (GHz).a d voltage is produced across the junction voltage is diretly propotinal to frequenccy
as the bias current was increased the voltage increased in a number of equal steps of constant voltage.the voltage is particular step is given by
v = (f.n.h)/(2e)
ok lah da ngantok bgt ini...tido dlu.....to be cotinued kkkk......zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
