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

Questions
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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