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12th Grade > Physics

UNITS AND DIMENSIONS MCQs

Total Questions : 40 | Page 1 of 4 pages
Question 1. Dimensions of coefficient of viscosity are
  1.    ML2T−2
  2.    ML2T−1
  3.    ML−1T−1
  4.    MLT
 Discuss Question
Answer: Option C. -> ML−1T−1
:
C
F=η.Advdx[η]=[ML1T1] where A is the area, v the velocity and dx the change in displacement.
Question 2. From the equation tan θ=rgv2 , one can obtain the angle of banking θ for a cyclist taking a curve (the symbols have their usual meanings). Then say, it is
  1.    Both dimensionally and numerically correct
  2.    Neither numerically nor dimensionally correct
  3.    Dimensionally correct only
  4.    Numerically correct only
 Discuss Question
Answer: Option C. -> Dimensionally correct only
:
C
Given equation is dimensionally correct because both sides are dimensionless but numerically wrong because the correct equation is tanθ=v2rg.
Question 3. The frequency of vibration f of a mass m suspended from a spring of spring constant K is given by a relation of this type f =CmxKy; where C is a dimensionless quantity. The value of x and y are 
  1.    x = 12, y = 12
  2.    x = -12, y = - 12
  3.    x = 12, y = - 12
  4.    x = - 12, y = 12
 Discuss Question
Answer: Option D. -> x = - 12, y = 12
:
D
By putting the dimensions of each quantity both sides we get [T1]=[M]x[MT2]y
Now comparing the dimenstions of quantities in both sides we get x+y =0 and 2y =1
x = - 12,y = 12
Question 4. Dimensional formula ML1T2 does not represent the physical quantity 
  1.    Young's modulus of elasticity
  2.    Stress
  3.    Strain
  4.    Pressure
 Discuss Question
Answer: Option C. -> Strain
:
C
Strain =ΔLL dimensionless quantity
Question 5. If the speed of light (c), acceleration due to gravity (g) and pressure (p) are taken as the fundamental quantities, then the dimension of gravitational constant is 
  1.    c2g0p−2
  2.    c0g2p−1
  3.    cg3p−2
  4.    c−1g0p−1
 Discuss Question
Answer: Option B. -> c0g2p−1
:
B
Let [G] cxgypz
by substituting the following dimensions :
[G] = [M1L3T2],[c]=[LT1],[g]=[LT2]
[p]=[ML1T2]
compare the dimension of M, L and T onboth sides
we can get x=0,y=2,z=1
[G]c0g2p1
Question 6. The physical quantity which has dimensional formula as that of EnergyMass X Length is
  1.    Force
  2.    Power
  3.    Pressure
  4.    Acceleration
 Discuss Question
Answer: Option D. -> Acceleration
:
D
EnergyMass×Length=[ML2T2][M][L]=[LT2]
This has the same dimension as acceleration.
Question 7. The dimension of  1ϵ0μ0 is that of
  1.    Velocity
  2.    Time
  3.    Capacitance
  4.    Distance
 Discuss Question
Answer: Option A. -> Velocity
:
A
Speed of light =1ϵ0μ0
Therefore the dimension of the quantity is same as velocity.
Question 8. Dimensional formula ML1T2 does not represent the physical quantity
  1.    Young's modulus of elasticity
  2.    Stress
  3.    Strain
  4.    Pressure
 Discuss Question
Answer: Option C. -> Strain
:
C
Strain =ΔLL dimensionless quantity
Question 9. The SI unit of universal gas constant (R) is
  1.    Watt K−1 mol−1
  2.    Newton K−1 mol−1
  3.    Joule K−1 mol−1
  4.    Erg K−1 mol−1
 Discuss Question
Answer: Option C. -> Joule K−1 mol−1
:
C
PV = nRT R = PVnT = Joulemole×Kelvin=JK1mol1
Question 10. The length, breadth, and thickness of a block are given by l = 12 cm, b = 6 cm and t = 2.45 cm The volume of the block according to the idea of significant figures should be
  1.    1 ×102 cm3
  2.    2 ×102 cm3
  3.    1.763 ×102 cm3
  4.    None of these
 Discuss Question
Answer: Option B. -> 2 ×102 cm3
:
B
Volume V = l × b × t
= 12 × 6 × 2.45 = 176.4 cm3
V = 176.4 ×102cm3
Since, the minimum number of significant figure is one in breadth, hence volume will also contain only one significant figure. Hence, V = 2 ×102cm3.

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