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Need for measurements, units of measurement, system of units, fundamental and derived units in SI, measurement of length, mass and time. Accuracy and precision of measuring instruments, errors in measurement. Significant figures.
Introduction
Need for measurements: |
Physics is a science of measurement. It is to provide a proper description of any natural phenomenon. |
Physical quantities: |
A quantity which is subjected to measurement may be treated as a physical quantity. |
Units of measurement: |
>The unit >and numerical value |
|
System of Units
S.No. |
Name |
Unit |
Symbol |
1. |
length |
metre |
m |
2. |
mass |
kilogram |
kg |
3. |
time |
second |
s |
4. |
electric current |
ampere |
A |
5. |
temperature |
kelvin |
K |
6. |
amount of substance |
mole |
mol |
7. |
luminous intensity |
candela |
cd |
8. |
plane angle |
radian |
rad |
9. |
solid angle |
steradian |
sr |
. |
4 fundamental systems: |
i) CGS (cm,gram,sec) |
iii) FPS (ft,lb,sec) |
. |
. |
ii) SI (the above table of units) |
iv) MKS (m,kg,sec) |
|
Conversions
1 kilo m |
103m |
1 centi m |
10-2m |
1 milli m |
10-3m |
1 micron |
10-6m |
1 nano m |
10-9m |
1 angstrom |
10-10m |
1 X-unit |
10-13m |
1 fermi |
10-15m |
~ |
~ |
1 astronomical unit (AU) |
1.5 x 1011m |
1 light year (ly) |
1016m |
1 parallactic sound/parsec (pc) |
3.26 x 1016m |
|
Derived units
Volume |
length x breadth x height (m3) |
Density |
mass/volume (kg m-3) |
Velocity |
displacement/time (m-1) |
Acceleration |
change in velocity/time (ms-2) |
Force |
mass x acceleration (kg m s-2) |
Pressure |
force/area (N m-2) |
Work |
force x displacement (kg m2s-2) |
Power |
work/time (J s-1) |
Measurement of length
Direct methods |
Least count= Pitch/ no. of divisions |
Vernier calliper |
0.01cm |
Screw Gauge |
0.001cm |
Spherometer |
0.001cm |
Indirect methods |
full form |
Echo |
(reflection) |
RADAR |
Radio Detection And Ranging |
LASER |
Light Amplification by Stimulated Emission of Radiation |
SONAR |
Sound Navigation And Randing |
Errors in measurement
Systematic errors |
What is it? |
Instrumental errors |
errors due to defected alignment |
Error due to imperfection |
imperfection of apparatus |
Gross errors |
improper adjustment of setup |
Random Errors |
> |
_Small changes in conditions of experiment |
_Incorrect judgement of the observer |
Methods to express an error |
how? |
Absolute Error |
The difference between the true and measured value |
Mean Error |
Arithmetic mean of errors of different measurements |
Relative/Fractional Error |
Ratio of mean error to the true value |
Percentage Error |
Fractional error multiplied by 100 |
Significant figures
Rules: |
i) decimal point does not effect |
ii) all 0's between two non-zeros are significant |
iii) all 0's to the right of non-zero digit and before the decimal point are not significant |
iv) all 0's after the decimal point are significant |
v) all 0's after the decimal point but before non-zeros are not significant |
|
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