**Units and dimensions Q&A**

**1. What is a physical quantity?**

Ans : Any quantity which is measurable is called physical quantity.

**2. Explain the term Fundamental Physical quantity.**

Ans: The physical quantity which is independent or which can not be derived from any other physical quantity is called fundamental physical quantity. EX: Mass, Length and Time.

**3.Explain the term Derived physical quantity. Give examples.**

Ans :The physical quantity which is dependent on other physical quantity or which is derived from other physical quantity is called derived physical quantity. Ex : Area, Electric charge, Magnetic field strength, power etc.

**4.How many fundamental quantities are there in C.G.S; F.P.S and M.K.S systems? What are they?**

Ans : There are 3 fundamentals quantities in C.G.S; F.P.S and M.K.S systems, they are mass, length and time.

**5.How many fundamental quantities are there in S.I systems? What are they?**

Ans : In S.I system 7 fundamental quantities are there, they are

- Mass
- Length
- Time
- Electric current
- Intensity of light
- Thermodynamic temperature
- Quantity of matter.

**6.How many supplementary quantities are there in S.I system? What are they?**

Ans : In S.I system there are 2 supplementary quantities, they are:

- Plane Angle
- Solid Angle.

**7. What are the units of length in C.G.S ; F.P.S and M.K.S systems.**

Ans : The units of length are cm,foot and meter respectively in C.G.S ; F.P.S and M.K.S systems .

**8. what are the units of fundamental quantities in S.I system?**

Ans : Mass → kg ; Length → m ; Time → sec ; Electric current → Amp Thermodynamic temperature → kelvin ;

Intensity of light → candela ; Quantity of matter → mole .

**9.what are the units of supplementary quantities in S.I system?**

Ans : Plane angle → radian ; Solid angle → steradian .

**10. Name the physical quantities whose dimensional formula is M^0L^1T^0 ?**

Ans : The physical quantities are:

- Distance or length
- Displacement
- Wave length

**11. Name the physical quantities whose dimensional formula is M^0L^1T^{-1} ?**

Ans : The physical quantities are:

- Speed
- Velocity

**12.Name the physical quantities whose dimensional formula is M^1L^2T^{-2}K^{-1} ?**

Ans : The physical quantities are:

- Thermal capacity
- Entropy

**13. Name the physical quantities whose dimensional formula is M^1L^1T^{-1} ?**

Ans : The physical quantities are:

- Momentum
- Impulse

**14. Name the physical quantities whose dimensional formula is M^1L^1T^{-2} ?**

Ans : The physical quantities are:

- Force
- Tension
- Weight

**15. Name the physical quantities whose dimensional formula is M^1L^2T^{-2} ?**

Ans : The physical quantities are:

- Work
- Energy
- Heat
- Moment of force
- Torque

**16. Name the physical quantities whose dimensional formula is M^1L^{-1}T^{-2}?**

Ans : The physical quantities are:

- Pressure
- Stress
- Young’s modulus
- Rigidity modulus
- Bulk modulus

**17. Name the physical quantities whose dimensional formula is M^0L^0T^{-1} ?**

Ans : The physical quantities are:

- Frequency
- Decay constant
- Angular velocity

**18. Name the physical quantities whose dimensional formula is M^1L^2T^{-1} ?**

Ans : The physical quantities are:

- Angular momentum
- Plank constant

**19. Name the physical quantities whose dimensional formula is M^1L^0T^{-2} ?**

Ans : The physical quantities are:

- Force constant
- Surface tension

**20. Which physical quantity has negative dimensions in mass ?
Ans : Gravitational constant (G).**

**21. State few constants which have dimensions ?**

Ans :Constants which have dimensions are:

- Plank’s constant (h)
- Velocity of light in vacuum (c)
- Permeability of free space (mu_0)
- Permittivity of free space (epsilon_0)
- Universal gravitational constant (G)
- Universal gas constant (R)
- Boltzmann constant (k)

**22 .which physical quantities have the unit henry ?**

Ans : self Inductance and Mutual Inductance have the unit henry .

**23. What are the dimensions of electric conductivity in mass , length and current.**

Ans : Electric conductivity has -1,-3 and 2 dimensions in mass, length and current respectively.

**24. What is the unit of electric conductivity in C.G.S and S.I systems?**

Ans : It has no unit in C.G.S system ; its unit in S.I system is Siemen/meter or S/m.

**25. What are the uses of Dimensional methods?**

Ans : The uses of dimensional methods are:

- To convert units from one system to another.
- To check the correctness of equations connecting physical quantities.
- To derive the expressions connecting physical quantities.

**26. Which is the physical quantity whose S.I unit is Am ?**

Ans: Magnetic pole strength.

**27. V/m or N/Coulomb are the units of ……. Physical quantity.**

Ans : These are the units of Electric field strength.

**28. Name five physical quantities which neither have dimensions nor units.**

Ans : Refractive Index , specific gravity, susceptibility, dielectric constant, coefficient of friction.

**29. If V = Xt+Y ; V is the velocity , t is time.What are the dimensional formulas of X and Y ?**

Ans : According to principle of homogeneity of dimensions, the dimensions of M,L and T in every term should be same.

Therefore M^0L^1T^{-1} = X M^0L^0T^1 → X = frac{M^0L^1T^{-1}}{ M^0L^0T^1} ; X → L^1T^{-2} and Y→ L^1T^{-1}

**30.Which physical quantities does not possess dimensions in mass ?**

Ans :Area, volume, velocity, acceleration, angular displacement, angular velocity, angular acceleration.

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