Units
Basic
physical quantities
|
length |
meter |
m |
|
mass |
kilogram |
kg |
|
time |
second |
s |
|
temperature |
Kelvin |
K |
|
Luminous
intensity |
Candela |
cd |
|
Current |
Ampere |
A |
|
Plane Angle |
Radian |
rad |
|
Solid angle |
Steradian |
sr |
Derived
physical quantities
|
Force |
Newton (N) |
|
Pressure |
Pascal (Pa) |
|
Energy |
Joule (J) |
|
Frequency |
Hertz (Hz) |
|
Electric
charge |
Coulomb ( C) |
|
Electromotive
force |
Volt (V) |
|
Electrical
resistance |
Ohm () |
|
Electrical
conductance |
Siemens (S) |
|
Electrical
Flux |
Henry (H) |
|
Capacity |
Farad (F) |
|
Magnetic
flux |
Weber |
|
Magnetic
flux density |
Tesla (T) |
Measurement
Measurement
have a value and a unit.
Least
count
Smallest possible accurate reading that could be
obtained from scale of a measuring instrument is called the least count of the
measuring instrument.
Systematic
errors
Results from faulty measuring instruments, like
slowly running stop watches, incorrectly calibrated instruments, instruments
with zero errors. These are predictable & are typically constant or proportional to the
true value.
Ex - Zero Error - Zero error is defined as the condition where a measuring
instrument registers a reading when there should not be any reading.
-How to
eliminate
1.
Calibration of instruments, apparatus and making necessary corrections
2. Checking
for zero error before taking readings
Random
errors
Value depends on the observer who use instrument.
To eliminate this error few readings are taken and mean value is obtained.
Fractional
error
Percentage
error
·
Least count is the smallest possible
measurement that could be obtained with accuracy from a measuring instrument.
·
Accuracy of a measurement is considered
to be sufficient if percentage error is less than or equal to 1%.
Vernier
principle
In a Vernier scale,
Least count (L)
Value of a main scale unit (M)
Value of a Vernier scale unit (V)
Screw
principle
In an instrument using screw principle,
Least count (L)
Pitch of the screw (p)
Divisions on the circular scale (n)
.END.
