# Class 11th Physics – 2 Units and Measurements MCQs

#### What would be the mass of body that weighs 2 N at a place where g = 9.8 m/s^{2} ____.

Here, W = 2 N, g = 9.8 m/s^{2}
∴m = w/g = 2/9.8 = 0.204 kg

#### Which of the following system of units is not based on mass, length and time alone?

SI is based on seven basic units and two supplementary units.

#### In the equation y = A sin (ωt - kx), where x is distance and t is time, then the dimensional formula of ω and k are respectively ____.

angle is dimensionless,

ωt = θ/t = 1/T= T^{-1}

Therefore, ω = [M^{0}L^{0}T^{-1}]

Since kx = θ, k = θ/x = 1/L=L^{-1}

Therefore, k = [M^{0}L^{-1}T^{0}]

#### The length of one rod (l_{1}) = 3.323 cm and the other is (l_{2}) = 3.321 cm. If both rods were measured with one measuring instrument with least count 0.001 cm, then (l_{1} - l_{2}) is ____

l_{1} - l_{2} = (3.323 ± 0.001) - (3.321 ± 0.001)
= (0.002 ± 0.002) cm

#### 16. The least count of a stop watch is 0.2 sec. The time of 20 oscillations of a pendulum is measured to be 25 sec. Then, the percentage error in the measurement of time will be ____.

0.225×100 = 0.8%

#### The dimensions of kinetic energy is ____.

M (L T^{-1})^{2} = M^{1} L^{2} T^{-2}
∵1/2 has no dimension

#### The significant figure of 5.4 × 0.125 is ____.

5.4 × 0.125 (Multiply normally) = 0.675 = 0.68 (Rounding off according to significant figures)

#### If R is the distance of the moon from earth, θ the angle subtended by the moon at the earth, then D the diameter of the moon is given by

If R is the distance of the moon from earth, θ the angle subtended by the moon at the earth, then D the diameter of the moon is given by D = Rθ.

#### The order of age of earth is ____.

The age of universe is of the order 10^{17} s.

#### If a screw gauge has 200 equal divisions marked along the circumference of the disc and one full rotation of the disc advances on the main scale by 0.05 cm, then the least count of the screw gauge is ____.

L.C = Pitch/No. of division in circular scale = 0.05/200 = 2.5 × 10^{-4} cm

#### Which among the following - Impulse, force, momentum, work have same dimensions ____ .

Impulse = force × time
= [M L T^{-2}] × T = [M^{1} L^{1} T^{-1}]
Momentum = mass × velocity
M × [L T^{-1}] = [M^{1} L^{1} T^{-1}]

#### The dimensions of permittivity of free space is ____.

According to coulomb's law,
F = ε_{0} = q^{2 }/(F)(r^{2 }) = A^{2}T^{2 }/(MLT^{- 2 }) (L^{2 }) = M^{- 1}L^{- 3}T^{4}A^{2}

#### 2Which of the following is not a unit of radiation?

The tesla (symbol T) is the SI derived unit of magnetic field B (which is also known as "magnetic flux density" and "magnetic induction").

#### The length 'l' of a cylinder is given as 1.0 cm. The least count of the instrument used to measure length is ____.

Significant figures are used to express the order of accuracy of a measurement. If we write l = 1.0 cm, it means that the least count of the instrument with which l is measured is 0.1 cm.

#### Pascal is the SI unit of

Pascal is the SI unit of stress

#### The correct order of units for the following will be

The distance between earth and stars is measured in Light years. The size of nucleus is measured in Fermi. The interatomic distance in a solid is measured in Angstrom.

#### If the error in the measurement of radius of sphere is 1%, then the error in the measurement of volume is ____.

V = 4/3Πr^{3}

#### If the diameter of a sphere is measured with an instrument having least count 0.001 cm, the diameter is 1.933 cm, then the radius to correct significant figures will be ____.

radius = diameter/2 = 1.933/2 = 0.9665 = 0.966 cm, this is according to the rule "rounding to even."

#### The weight of a body is 30 gm. The statement made above is not correct because

Weight is a force. The unit of force is newton. Hence, weight should be expressed in newton.

#### ___ is not a unit of length.

Options a, b & c are units of length while d is unit of angle in a plane.

#### Parallactic second is the largest unit of

One parallactic second is the distance corresponding to a parallax 3.26 light year (approx.).

#### The smallest mass measured so far is ____.

The smallest mass measured so far is that of an e- which is≈10^{-30}k.

#### Which is most accurate significant figure among the given options ____.

3.000m because it has maximum no. of significance .

#### In physics, one shake equals ____.

Shake is a unit of time used in microscopic physics. One shake equals 10^{-8} s.

#### The order of mass of universe is ____.

The mass of universe is of the order 10^{55} kg.

#### If the rotational K.E of a body is 1/2 I ω^{2}, then the dimension of I is ____.

K . E = 1/2Iω^{2}
∴I = 2×K .E/ω^{2}
= ML^{2}T^{- 2}/T^{- 2} = M^{1}L^{2}T^{0}
The dimension of I is ML^{2}T^{- 2}/T^{- 2} = M^{1}L^{2}T^{0}.

#### 'atto' is equal to 10^{x}. The value of x in 10^{x} is

Atto- (symbol a) is a prefix in the metric system denoting a factor of 10^{−18}

#### The significant figure of 0.99 - 0.989 is ____.

0.99 - 0.989 = 0.001 = 0.01 × 10^{-1}

#### If pressure depends on distance, P =α/β exp( -αz/kϴ) where α, β are constants, z = distance, k = Boltzman's constant and θ = temp, then the dimension of β is ____.

Unit of k is joules per Kelvin.
Since 0 dimension of k = [M L^{2} T^{-2} θ^{-1}], dimensional formula for α = (ML^{2}T^{- 2}ϴ)/ (L)
Since Dimensional formula of P =[M L^{-1}T^{-2}], dimensional formula for
β = (M LT^{2})/(ML^{-1}T^{2} )= M^{0}L^{2}T^{0}

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