Measurements and Experimentation Solutions

Ans: The three requirements for selecting a unit of a physical quantity are —

1. The unit should be of convenient size.
2. It should be possible to define the unit without any ambiguity.
3. The unit should be reproducible.
4. The value of unit should not change with space and time (i.e., it must always remain same everywhere).

Ans: The fundamental units in S.I. system along with their symbols are as follows —

Ans: The units of quantities other than those measured in fundamental units can be expressed in terms of the fundamental units and they are called derived units.

Thus, derived units are those which depend on the fundamental units or which can be expressed in terms of the fundamental units.

Example: For the measurement of area, we need to measure length and breadth in the unit of length and then express area in a unit which is: length × length or (length)².

Ans: The units of length which are bigger than a metre are —

1. Astronomical Unit (A.U.) — One astronomical unit is equal to the mean distance between the earth and the sun.
   Relation: 1 A.U. = 1.496 × 10¹¹ m
2. Light year (ly) — A light year is the distance travelled by light in vacuum in one year.
   Relation: 1 light year = 9.46 × 10¹⁵ m

Ans: The 3 convenient units used to measure length ranging from very short to very long value are —

1. Centimeter (cm)
2. Metre (m)
3. Kilometer (km)

S.I. unit of length is meter (m). Relations:

• 1 m = 100 cm
• 1 km = 1000 m

Ans: The S.I. unit of mass is kilogram (kg).

One kilogram is defined as the mass of a cylindrical piece of platinum-iridium alloy kept at International Bureau of Weights and Measures at Serves near Paris.

Ans: The two units of mass smaller than a kilogram (kg) are:

1. gram (g) — Relation: 1 g = 10^-3 kg
2. milligram (mg) — Relation: 1 mg = 10^-6 kg

Ans: The two units of mass bigger than a kilogram (kg) are:

1. Quintal — It is one hundred times a kilogram.
   Relation: 1 quintal = 100 kg
2. Metric tonne — It is one thousand times a kilogram.
   Relation: 1 metric tonne = 1000 kg

Ans: The S.I. unit of time is second (s).

A second can be defined as 1/86400th part of a mean solar day, i.e.,

1 s = (1/86400) × one mean solar day

Ans: The two units of time bigger than a second (s) are:

1. Minute (min) — One minute is the duration of 60 seconds.
   Relation: 1 min = 60 s
2. Hour (h) — One hour is the duration of 60 minutes.
   Relation: 1 h = 3600 s