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Physics XI Notes for Physics Notes

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# Units and Dimensions Q & A

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

1. Mass
2. Length
3. Time
4. Electric current
5. Intensity of light
6. Thermodynamic temperature
7. 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:

1. Plane Angle
2. 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:

1. Distance or length
2. Displacement
3. Wave length

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

1. Speed
2. Velocity

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

1. Thermal capacity
2. Entropy

13. Name the physical quantities whose dimensional formula is M^1L^1T^{-1} ?
Ans : The physical quantities are:

1. Momentum
2. Impulse

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

1. Force
2. Tension
3. Weight

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

1. Work
2. Energy
3. Heat
4. Moment of force
5. Torque

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

1. Pressure
2. Stress
3. Young’s modulus
4. Rigidity modulus
5. Bulk modulus

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

1. Frequency
2. Decay constant
3. Angular velocity

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

1. Angular momentum
2. Plank constant

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

1. Force constant
2. 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:

1. Plank’s constant (h)
2. Velocity of light in vacuum (c)
3. Permeability of free space (mu_0)
4. Permittivity of free space (epsilon_0)
5. Universal gravitational constant (G)
6. Universal gas constant (R)
7. 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:

1. To convert units from one system to another.
2. To check the correctness of equations connecting physical quantities.
3. 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.