Unit, dimension and measurement is an important chapter for class 10, class 11 and first year engineering physics course. Different types of questions on this chapter are discussed below.
Unit and Dimension of some common physical quantity
| Physical quantity | CGS unit | SI unit | Dimension |
| 1. Velocity (Displacement/time) | cm/s | m/s | [LT-1] |
| 2. Acceleration (Change in velocity/time) | cm/s2 | m/s2 | [LT-2] |
| 3. Force (mass \times acceleration) | dyne | newton (N) | [MLT-2] |
| 4. Pressure (force/area) | dyne/cm2 | N/m2 (Pa) | [ML-1T-2] |
| 5. Area | cm2 | m2 | [L2] |
| 6. Volume | cm3 | m3 | [L3] |
| 7. Density (mass/volume) | gm/cm3 | kg/m3 | [ML-3] |
| 8. Momentum (mass \times velocity) | gm.cm/s | kg.m/s | [MLT-1] |
| 9. Work/Energy (force \times displacement) | erg | joule | [ML2T-2] |
| 10. Power (Work done/time) | erg/s | J/s (watt) | [ML2T-3] |
Short answer type questions on unit, dimension and measurement for different board exams and engineering physics course
1. Write down the fundamental units in SI system.
There are 7 fundamental units in SI system which are given as follows
1. Length – metre
2. Mass – kilogram
3. Time – second
4. Current – ampere
5. Temperature – kelvin
6.Luminous intensity – candela
7. amount of substance – mole
2. Prove 1N = 105 dyne by using dimensional analysis.
The SI unit of force is newton and CGS unit is dyne.
Let 1newton = n dyne
The dimension of force is [MLT-2]
assume the fundamental units in SI and CGS system are M1,L1,T1 and M2,L2,T2
Therefore, 1newton = n dyne
1 \times [M_{1}L_{1}T_{1}^{-2}] = n [M_{2}L_{2}T_{2}^{-2}]
n=[(\frac{M_{1}}{M_{2}})^{1}(\frac{L_{1}}{L_{2}})^{1}(\frac{T_{1}}{T_{2}})^{-2}]
M1 =1kg, L1 = 1m, T1 =1s and M2=1gm, L2= 1cm,T2= 1s
n=[(\frac{1kg}{1gm})^{1}(\frac{1m}{1cm})^{1}(\frac{1s}{1s})^{-2}]
n=[(\frac{10^{3}gm}{1gm})^{1}(\frac{10^{2}cm}{1cm})^{1}(\frac{1s}{1s})^{-2}]
n=10^{3} \times 10^{2}
n=10^{5}
3. State two limitations of dimensional analysis.
The limitations of dimensional analysis are
1. This method can not give any information about dimensionless constants.
2. Composite relations can not be derived from this method.
3. Relations containing logarithmic functions, exponential functions and trigonometric functions can not be derived using dimensional analysis.
4. What are different types of errors.
In general, there are two types of errors.
1. Systematic error and 2. Random error
Systematic error: When the causes of the error are known, then the errors are called systematic errors. Some examples of systematic errors are instrumental errors and error due to external causes like pressure, temperature etc.
Random errors: When the causes of errors are not known precisely, the errors are called random errors.
5. What is accuracy and precision?
Accuracy measures how close the measured value to the correct value.
Precision gives how close the measured values are to one another.
MCQ questions on unit dimension and measurement for board exams, engineering physics course, jelet, neet, jee, cuet
| MCQ questions on unit and dimension | click here |
| Numerical on errors in measurement | click here |
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