CBSE Class 11 Physics Units Dimensions Vectors Assignment.

Comprehension

In the study of physics, we often have to measure the physical quantities. The numerical value of a measured quantity can only be approximate as it depends upon the least count of the measuring instrument used. The number of significant figure in any measurement indicates the degree of precision of that measurement. The importance of significant figure lies in calculation. A mathematical calculation cannot increase the precision of a physical measurement. Therefore, the number of significant figure in the sum or product of a group of numbers cannot be greater than the number that has the least number of significant figures. A chain cannot be stronger than its weakest link.

1. A bee of mass 0.000087 kg sits on a flower of mass 0.0123 kg. What is the total mass supported by the stem of the flower upto appropriate significant figures?
(a) 0.012387 kg (b) 0.01239 kg (c) 0.0124 kg (d) 0.012 kg

2. The radius of a uniform wire is r = 0.021 cm. The value π is given to be 3.142. What is the area of cross-section of the wire upto appropriate significant figures?
(a) 0.0014 cm² (b) 0.00139 cm² (c) 0.001386 cm2 (d) 0.0013856 cm²

3. A man runs 100.5 m in 10.3 s. Find his average speed upto appropriate significant figures.
(a) 9.71 ms^–1 (b) 9.708 ms^–1 (c) 9.7087 ms^–1 (d) 9.70874 ms^–1

Each of the questions given below consists of two statements, an assertion (A) and reason (R).
Select the number corresponding to the appropriate alternative as follows
(a) If both A and R are true and R is the correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) If A is true but R is false
(d) If A is false but R is true

4. A: Light year is a unit of time.
R: Light year is the distance travelled by light in vacuum in one year.

5. A: nm is not same as mN
R: 1 nm = 10^–9 m and 1 mN = 10^–3 N

6. A: Planck’s constant has the dimensions of angular momentum.
R: Both represent product of energy and time

7. A: Parallax method is used for measuring distances of nearby stars only.
R: With increase of distance of star, parallactic angle becomes too small to be measured accurately.

8. A. Pressure has the dimensions of energy density.
R. Energy density =  energy//volume = ML²T^-2/L³⁼ [ML^–1T^–2] = pressure

9. A. The dimensions of rate of flow are [M⁰L³T^–1]
R. Rate of flow is velocity/sec.

10. A. Specific gravity of liquid is a dimensionless quantity.
R. It is the ratio of density of fluid to the density of water.

Miscellaneous Assignment

1. (c) 2. (a) 3. (a) 4. (d) 5. (a) 6. (b) 7. (a) 8. (a) 9. (c) 10. (a)