A to Z of Physics: 2008

Tuesday, December 30, 2008

Multiple choice questions, Units - Dimensions

1 . 1KWH is unit of

Ans : 1.Time 2. Power 3. Energy 4. Stress

2. Unit of Intensity of magnetic induction field is

Ans : 1.N/Am 2. Tesla 3.Wb $m^{-2}$ 4. All above

3. Which of the following has no units?

Ans : 1. Thermal capacity 2. Magnetic susceptibility 3. Angular acceleration 4. Moment of a magnet

4.Which one of the following units is a fundamental unit?

Ans : 1. watt 2. joule/sec 3. ampere 4. newton

5. $10^5$ Fermi is equal to

Ans : 1. 1 meter 2. 100 micron 3. 1angstrom unit 4. 1 mm

6. kg m/sec is the unit of

Ans : 1. Impulse 2. Angular acceleration 3 . Capacity of condenser 4. Acceleration.

7. candela is the unit of

Ans : 1. Magnetic flux 2. Intensity of electric field 3. Luminous intensity 4. Charge

8. If 10 newton = X dynes, the value of x is

Ans : 1. $10^6$ 2. $10^4$ 3. $10^8$ 4. $10^3$

9. 1 KWh is equal to

Ans : 1. 360 J 2. 1800 J 3. $1800\times10^5$ J 4. $360\times10^5$ J

10. Which of the following is a common unit of a physical quantity in M.K.S & S.I systems.

Ans : 1. ampere 2.kelvin 3. mole 4. joule/sec

11. The fundamental unit which is common in F.P.S and M.K.S systems is

Ans : 1. foot 2. sec 3. kilo gram 4. pound

12. Which of the following is Unit of time?

Ans 1. Lunar Month 2. Kelvin 3. candela 4. Light year

13. Boltzman’s constant and planck’s constant differ in the dimensions of

Ans : 1. Time and temperature 2. Mass and temperature 3. Length and mass 4. Length and time .

14. Magnetic induction and magnetic flux differ in the dimensions of

Ans : 1 Time 2. Mass 3.Electric current 4.Length

15.Which of the following is a fundamental quantity in M.K.S and C.G.S systems.

16 . rad / sec is the unit of

Ans : 1.Angular displacement 2. Angular velocity 3. Angular acceleration 4. Angular momentum .

17 . The ratio of S.I unit of K.E to C.G.S unit of K.E is

Ans : 1. $10^7$ 2. $10^{-7}$ 3. $10^{-5}$ 4. $10^5$

18. If $u_1$ and $u_2$ are the units of a physical quantity and $n_1$ ‘ $n_1$ are the numerical values, then

Ans : 1. $\frac{n_1}{n_2} =\frac{u_1}{u_2}$ 2. $\frac{n_2}{n_1} =\frac{u_1}{u_2}$ 3. $\frac{n_1}{n_2}^2 =\frac{u_1}{u_2}$ 4. None of the above

19. which one of the following is the unit of energy.

Ans : 1. newton 2. N/sec 3. N - sec 4.None of the above

units-Dimensions ( QA)

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 : To convert units from one system to another. ii )To check the correctness of equations connecting physical quantities iii )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.

units-Dimensions ( QA)

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 i) Mass ii)Length iii)Time iv)Electric current v)Intensity of light vi) Thermodynamic temperature vii) 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 i) Plane Angle ii) 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 i)Distance or length ii) displacement iii)wave length

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

Ans : The physical quantities are i) speed ii) velocity

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

Ans : The physical quantities are i)Thermal capacity ii) Entropy

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

Ans : The physical quantities are i)Momentum ii) impulse .

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

Ans : The physical quantities are i)force ii ) Tension iii) weight .

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

Ans : The physical quantities are i) Work ii) Energy iii) Heat iv)Moment of force Iv) Torque .

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

Ans : The physical quantities are i) pressure ii ) stress iii) Young’s modulus iv) Rigidity modulus v) Bulk modulus .

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

Ans : The physical quantities are i) frequency ii) Decay constant iii)Angular velocity .

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

Ans : The physical quantities are i )angular momentum ii )Plank constant .

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

Ans : The physical quantities are i )Force constant ii )surface tension .

20. Which physical quantity has negative dimensions in mass ?

Ans : Gravitational constant (G) .

21. State few constants which have dimensions ?

Ans : i) Plnak’s constant (h) ii)Velocity of light in vacuum (c) iii)Permeability of free space ( $\mu_0$ ) iv) Permittivity of free space ( $\epsilon_0$ ) v)Universal gravitational constant (G) vi) Universal gas constant (R)

vii)Boltzmann constant (k) .

22 .which physical quantities have the unit henry ?

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

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Monday, December 29, 2008

Table of Units,dimensional Formulas of physical quantities.

Fundamental Physical Quantities:

S.No	Fundamental Physical Quantity	Formula	Dimensional Formula	S.I Unit of physical quantity
1.	Mass	Amount of matter in the object	M	kg
2.	Length		L	meter
3.	Time		T	sec
4.	Electric current		I or A	ampere
5.	Amount of substance		N	mole(mol)
6.	Luminous intensity		J	candela(cd)
7.	Temperature		K or $\theta$	Kelvin

Derived Physical Quantities:

S.No	Derived Physical Quantity	Formula	Dimensional Formula	S.I Unit of physical quantity
1.	Area	$l\times b$	[ $M^0L^2T^o$ ]	$m^2$
2.	Volume	$l\times b\times h$	[ $M^0L^3T^o$ ]	$m^3$
3.	Density	$\frac{M}{V}$	[ $M^1L^{-3}T^0$ ]	$kg/m^3$
4.	Specific Gravity	$\frac{Density of Substance}{Density of Water}$	[ $M^0L^0T^0$ ]	No units
5.	Frequency	$\frac{no of vibrations}{Time}$	[ $M^0L^0T^{-1}$ ]	hertz
6.	Angle	$\frac{Arc}{radius}$	$M^0L^oT^o$	No units
7.	Velocity	$\frac{Displacement}{time}$	$M^0L^1T^{-1}$	m/sec
8.	Speed	$\frac{Distance}{time}$	$M^0L^1T^{-1}$	m/sec
9.	Areal velocity	$\frac{Area}{time}$	$M^0L^2T^{-1}$	$m^2sec^{-1}$
10.	Acceleration	$\frac{Change in velocity }{time}$	$M^0L^1T^{-2}$	$m/sec^2$
11.	Linear momentum	$M\times V$	$M^1L^1T^{-1}$	kg m/sec
12.	Force	$mass\times acceleration$	$M^1L^1T^{-2}$	kg-m/ $sec^2$ or Newton
13.	Weight	w=mg	$M^1L^1T^{-2}$	kg-m/ $sec^2$ or Newton
14.	Moment of force/Torque/Couple	$Force\times arm$	$M^1L^2T^{-2}$	kg $m^2sec^{-2}$
15.	Impulse	$Force\times time$	$M^1L^1T^{-1}$	kg m/sec or Ns
16.	Pressure	$\frac{Force}{Area}$	$M^1L^{-1}T^{-2}$	N/ $m^2$ or Pa
17.	Work	$Force\times Distance$	$M^1L^2T^{-2}$	Nm or Joule
18.	Kinetic Energy	$\frac{1}{2} mv^2$	$M^1L^2T^{-2}$	joule
19.	Potential Energy	mgh	$M^1L^2T^{-2}$	joule
20.	Gravitational constant	$\frac{Force\times (Length)^2}{(mass)^2}$	$M^{-1}L^3T^{-2}$	$kg^{-1}m^3sec^{-2}$
21.	Gravitational field strength	$\frac{Force}{mass}$	$M^0L^1T^{-2}$	$N kg^{-1}$
22.	Gravitational Potential	$\frac{Work}{mass}$	$M^0L^2T^{-2}$	$J kg^{-1}$
23.	Force constant (k)	$\frac{F}{L}$	$M^1L^0T^{-2}$	$N m^{-1}$
24.	Power	$\frac{Work}{time}$	$M^1L^2T^{-3}$	W or J/sec
25.	Moment of Inertia ( I )	$Mass\times Distance^2$	$M^1L^2T^{0}$	kg $m^2$
26.	Stress	$\frac{Force}{Area}$	$M^1L^{-1}T^{-2}$	N/ $m^2$ or Pa
27.	Strain	$\frac{Change in length}{Origional length}$	$M^0L^0T^0$	No units
28.	Modulus of Elasticity	$\frac{Stress}{Strain}$	$M^1L^{-1}T^{-2}$	N/ $m^2$ or Pa
29.	Poission’s Ratio	σ = $\frac{Y}{2n}$ -1	$M^0L^0T^0$	No units
30.	Velocity gradient	$\frac{Change in velocity}{Distance}$	$M^0L^0T^{-1}$	$sec^{-1}$
31.	Coefficient of dynamic viscosity	$\frac{Tangential stress}{Velocity Gradient}$	$M^1L^{-1}T^{-1}$	kg $m^{-1}sec^{-1}$ (or) N-sec/$latex \m^2$ (or)pascal-sec (or)poiseuille
32.	Surface Tension	$\frac{Force}{Length}$	$M^1L^0T^{-2}$	$kg sec^2$ ,N/m
33.	Angular displacement ( $\theta$ )	$\frac{Arc}{radius}$	$M^0L^oT^o$	no Units
34.	Angular velocity(ω)	$\frac{Angular displacement}{Time}$	$M^0L^oT^{-1}$	rad/sec
35.	Angular acceleration(α)	$\frac{Change in angular velocity}{Time}$	$M^0L^oT^{-2}$	rad/ $sec^{-2}$
36.	Angular momentum	Iω	$ML^2T^{-1}$	$kg-m^2 sec^{-1}$
37.	Angular Impulse	Iω	$ML^2T^{-1}$	$kg-m^2 sec^{-1}$
38.	Temperature		$\theta$ or K	kelvin or degree Celsius
39.	Coefficient of linear expansion(α)	$\frac{l_2-l_1}{l_1\times Temp(t_2-t_1)}$	$M^0L^0T^0K^{-1}$	/kelvin
40.	Specific heat	$\frac{Energy}{Mass\times Temp}$	$M^0L^2T^{-2}K^{-1}$
41.	Latent heat	$\frac{Energy}{Mass}$	$M^0L^2T^{-2}$	$joule-kg^{-1}$
42.	Entropy	$\frac{Q}\theta$	$M^1L^2T^{-2}K^{-1}$	$J K^{-1}$
43.	Thermal capacity	$\frac{H}\theta$	$M^1L^2T^{-2}K^{-1}$	$J K^{-1}$
44.	Gas constant	$\frac{PV}{m T}$	$M^0L^2T^{-2}K^{-1}$	$joule-K^{-1}$
45.	coefficient of thermal conductivity	$\frac{Qd}{A(\theta_2-\Theta_1)t}$	$M^1L^1T^{-3}K^{-1}$	$W m^{-1}K^{-1}$
46.	Pole strength	$Ampere\times meter$	$M^0L^1T^0I$	Am
47.	Magnetic Moment		$M^0L^2T^0I^1$	$Amp-m^2$
48.	Magnetic flux $\phi$		$ML^2T^{-2}I^{-1}$	weber ; $T-m^{2}$ ;J/Amp
49.	Magnetic field,magnetic flux density (B)		$MT^{-2}I^{-1}$	Tesla; $J/A-m^{2}$
50.	Permeability of free space	$\frac{\mu}{\mu_r}$	$MLT^{-2}I^{-2}$	$NA^{-2}$
51.	Magnetic susceptibilty also called volumetric or bulk susceptibility χ_m	χ_m = μ_r − 1	$M^0L^oT^o$	no units
52.	Electric Charge	$I\times T$	$M^0L^0T^1I^1$	Amp sec , coul
53.	Electric potential	$\frac{Work}{Charge}$	$M^1L^2T^{-3}I^{-1}$	Volt
54.	E.M.F	$\frac{Work}{Charge}$	$M^1L^2T^{-3}I^{-1}$	Volt
55.	Electric Capacity	$\frac{q}{V}$	$M^{-1}L^{-2}T^4I^2$	Farad
56.	Electric Resistance	$\frac{V}{i}$	$M^1L^2T^{-3}I^{-2}$	Ohm (Ω) or volt/amp
57.	Resistivity $\rho$	$\frac{R A}{L}$	$M^1L^3T^{-3}I^{-1}$	Ohm mt (Ω-m)
58.	Conductivity $\sigma$	1/ $\rho$	$M^{-1}L^{-3}T^3I$	Siemens/m
59.	Permittivity $\varepsilon$	$\varepsilon = \varepsilon_r \varepsilon_0 = (1+\chi)\varepsilon_0$	$M^{-1}L^{-3}T^4I^2$	farad/m
60.	Electric conductance	$\frac{1}{R}$	$M^{-1}L^{-2}T^3I^2$	Siemens (or) mhos
61.	Electric power	$V\times I$	$M^1L^2T^{-3}I^{-1}$	Watt
62.	Electrical Impedance(Z)	$\frac{V}{i}$	$M^1L^2T^{-3}I^{-2}$	Ohm (Ω) or volt/amp
63.	Electrical admittance	1/Z(Reciprocal of electric impedance)	$M^{-1}L^{-2}T^3I^3$	Siemens (or) mhos
64.	Self Inductance(L)	$\displaystyle v=L\frac{di}{dt}$	$ML^2T^{-2}I{-2}$	weber/amp or Henry
65.	Boltzmann’s constant	$\frac{Energy}{Temp}$	$M^1L^2T^{-2}K^{-1}$	J/kelvin
66.	Stefan’s constant	$\frac{E}{A\theta^4}$	$M^1L^0T^3K^{-4}$	$W m^{-2}K^{-4}$
67.	Co-efficient of friction $\mu$	$\mu$ = $\frac{F}{N}$ ,N=Normal reaction	dimension less scalar	no units
68.	Dielectric constant $\varepsilon_r$	It is also called relative permittivity	dimension less	no units
69.	Planck’s constant	$E=h\nu$	$ML^2T^{-1}$	J.sec (or) eV.sec
70.	Refractive index	μ	$M^0L^oT^o$	no units
71.	Focal length(f)	Distance between center of the lens(mirror) to its focus	L	meter
72.	Power of a lens (P)	The reciprocal of the focal length of a lens in meters is called power of a lens; p=1/f	$L^{-1}$	diaptors
73.	Wave number	No.of waves/distance	$L^{-1}$	$m^{-1}$
74.	Wave length	Length of a wave	L	meter