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CLASS 11 PHYSICS CHAPTER ONE UNITS AND MEASUREMENT
1.1 Introduction
Physics is a quantitative science, based on measurement of physical quantities. (such as length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity).
Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit.
The units for the fundamental or base quantities are called fundamental or base units (such as metre, kilogram, second, ampere, kelvin, mole and candela).
The units of all other physical quantities can be expressed as combinations of the base units. Such units obtained for the derived quantities are called derived units.
A complete set of these units, both the base units and derived units, is known as the system of units.
Question 1. Fill in the blanks
(a) The volume of a cube of side 1 cm is equal to…………m3.
Answer: (a) Volume of cube, V = (1 cm)3 = (10-2 m)3 10-6 m3.
Hence, answer is 10-6

(b) The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to ……..(mm)2.
(b) Surface area = 2πrh + 2πr2 = 2πr (h + r)
= 2 x 22/7 x 2 x 10 (10 x 10 + 2 x 10) mm2 = 1.5 x 104 mm2
Hence, answer is 1.5 x 104.

(c) A vehicle moving with a speed of 18 km h-1 covers ………. m in 1 s.
(c) Speed of vehicle = 18 km/h = 18 x 1000/3600 m/s = 5 m/s ;
so the vehicle covers 5 m in 1 s.

(d) The relative density of lead is 11.3. Its density is …….. g cm-3 or ………. kg m-3.
(d) Density= 11.3 g cm-3
=11.3 x 103 kg m-3 [1 kg =103 g,1m=102 cm]
=11.3 x 103 kg m-4