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NCERT Solutions for class 11 Physics | Chapter 2 - Units and Measurements

(1) The numbers 2.745 and 2.735 on rounding off to 3 significant figures will give
[A] 2.75 and 2.74
[B] 2.74 and 2.73
[C] 2.75 and 2.73
[D] 2.74 and 2.74
Answer: 2.74 and 2.74
(2) The length and breadth of a rectangular sheet are 16.2 cm and 10.1cm, respectively. The area of the sheet in appropriate significant figures and error is
[A] 164 ± 3 cm2
[B] 163.62 ± 2.6 cm2
[C] 163.6 ± 2.6 cm2
[D] 163.62 ± 3 cm2
Answer: 164 ± 3 cm2

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(3) Which of the following pairs of physical quantities does not have same dimensional formula?
[A] Work and torque.
[B] Angular momentum and Planck’s constant.
[C] Tension and surface tension.
[D] Impulse and linear momentum.
Answer: Tension and surface tension.
(4) Measure of two quantities along with the precision of respective measuring instrument is

A = 2.5 m s-1 ± 0.5 ms-1 B = 0.10 s ± 0.01 s

The value of A B will be
[A] (0.25 ± 0.08) m
[B] (0.25 ± 0.5) m
[C] (0.25 ± 0.05) m
[D] (0.25 ± 0.135) m
Answer: (0.25 ± 0.08) m
(5) You measure two quantities as A = 1.0 m ± 0.2 m, B = 2.0 m ± 0.2 m. We should report correct value for √AB as:
[A] 1.4 m ± 0.4 m
[B] 1.41m ± 0.15 m
[C] 1.4m ± 0.3 m
[D] 1.4m ± 0.2 m
Answer: 1.4m ± 0.2 m
(6) Which of the following measurements is most precise?
[A] 5.00 mm
[B] 5.00 cm
[C] 5.00 m
[D] 5.00 km.
Answer: 5.00 mm
(7) The mean length of an object is 5 cm. Which of the following measurements is most accurate?
[A] 4.9 cm
[B] 4.805 cm
[C] 5.25 cm
[D] 5.4 cm
Answer: 4.9 cm
(8) Young’s modulus of steel is 1.9 × 1011 N/m2. When expr essed in CGS units of dynes/cm2, it will be equal to (1N = 105 dyne, 1m2 = 104 cm2)
[A] 1.9 × 1010
[B] 1.9 × 1011
[C] 1.9 × 1012
[D] 1.9 × 1013
Answer: 1.9 × 1012
(9) If momentum (P ), area (A) and time ( T ) are taken to be fundamental quantities, then energy has the dimensional formula
[A] (P1 A-1 T1)
[B] (P2 A1 T1)
[C] (P2 A-1/2 T1)
[D] (P1 A1/2 T-1)
Answer: (P1 A1/2 T-1)
(10) Which of the following are not a unit of time?
[A] Second
[B] Parsec
[C] Year
[D] Light year
Answer: B, D
(11) Which of the following ratios express pressure?
[A] Force/ Area
[B] Energy/ Volume
[C] Energy/ Area
[D] Force/ Volume
Answer: A, B
(12) If Planck’s constant (h ) and speed of light in vacuum (c ) are taken as two fundamental quantities, which one of the following can, in addition, be taken to express length, mass and time in terms of the three chosen fundamental quantities?
[A] Mass of electron (me)
[B] Universal gravitational constant (G)
[C] Charge of electron (e)
[D] Mass of proton (mp)
Answer: A, B, D
(13) Photon is quantum of radiation with energy E = hν where ν is frequency and h is Planck’s constant. The dimensions of h are the same as that of
[A] Linear impulse
[B] Angular impulse
[C] Linear momentum
[D] Angular momentum
Answer: B, D
(14) If P, Q, R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity?
[A] (P – Q)/R
[B] PQ – R
[C] (PR – Q2)/R
[D] (R + Q)/P
Answer: A, D
(15) Which is the most accurate atomic clock?
[A] Carbon-12 clock
[B] Carbon atom clock
[C] Caesium atom clock
[D] Stop clock
Answer: Caesium atom clock
(16) The product of energy and time is called action. The dimensional formula for action is same as that for
[A] Power
[B] Angular energy
[C] Force × velocity
[D] Impulse × distance
Answer: Impulse × distance
(17) After decimal point, number is less than 5 which is to be neglected,then retained number
[A] gets increased
[B] get decreased
[C] remains unchanged
[D] may decreased
Answer: remains unchanged
(18) Which pair of following quantities has dimensions different from each other
[A] Impulse and linear momentum
[B] Plank's constant and angular momentum
[C] Moment of inertia and moment of force
[D] Young's modulus and pressure
Answer: Moment of inertia and moment of force
(19) Planck's constant has the dimensions of :
[A] force
[B] energy
[C] linear momentum
[D] angular momentum
Answer: angular momentum
(20) A dimensionless quantity
[A] has no unit
[B] must have a unit
[C] cannot exist
[D] May have a unit
Answer: May have a unit

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