Class 10 - Physics - Chapter 2

Measurements

Definitions:

1. Meter

The length of the path traveled by light in vacuum in 1/299,792,458 of a second is known as meter.

Length is a fundamental unit used for measurements of length, distance and height. It is equal to the distance between two marks on a Platinum-Iridium bar kept at 0 C in International Bureau of Weight and Measurements (IBWM) near Paris.

2. Kilogram

The mass of a Platinum-Iridium cylinder kept at 0 C in International Bureau of Weight and Measurements (IBWM) near Paris is considered to be 1 kilogram.

Kilogram is a fundamental unit used for measurements of mass.

3. Second

It is equal to the duration of 9,192,631,770 periods of radiation of Cesium-133 in ground state.

Fundamental Units:

The international system of units is based on seven independent units known as Fundamental or Basic Units. These are given below:

1. Meter (m): length, distance, height (l)

2. Kilogram (kg): mass (m)

3. Second (s): time (t)

4. Ampere (A): electric current (I)

5. Kelvin (K): temperature (T)

6. Mole (mol): amount of substance (n)

7. Candela (cd): luminous intensity (Iv)

Derived Units:

The units that require two or more basic measurements of same units or different fundamental units for its definition are called derived units.

1. Square meter (m2): area (A)

2. Cubic meter (m3): volume (V)

3. Hertz (Hz): frequency (v)

4. Kilograms per cubic meter (kg/m3): mass density (p)

5. Meter per second m/s: speed velocity (V)

6. Radians per second (rad/s): angular velocity (w)

7. Meters per second square (m/s2): acceleration (a)

8. Newton (N) (kg.m/s2): force (F)

9. Pascal (Pa) (N/m2): pressure (P)

10. Joule (J)(N.m): work (W), energy(E), quantity of heat (q)

11. Watt (W) (J/s): power (P)

12. Coulomb (C) (A.s): quantity of electric charge (Q)

13. Volt (V) (W/A): potential difference (V), electromotive force (E)

14. Ohm (Omega): electric resistance (R)

15. Farad (F)(A.s/V): capacitance (C)

16. Weber (Wb)(V.s): magnetic flux (@)

17. Henry (H) (V.s/A): inductance (E)

18. Volts per meter (V/m): electric field strength (E)

19. Newton per coulomb (N/C): electric field strength (E)

20. Tesla (T) (Wb/m2): magnetic flux density (B)

21. Ampere per meter (A/m): magnetic field strength (H)

22. Joules per kilogram Kelvin: (J/kg.K) specific heat (Q)

Vernier Callipers:

A vernier calipers is an instrument that is used to measure the length, diameter and depth of solid substances accurately up to 0.1mm. A vernier calipers has two scales, the main scale (MS) and vernier scale (VS). The vernier scale (VS) slides over the main scale (MS).

Vernier Count (VC)

The smallest measurement that can be made with the help of a vernier calipers is known as least count of vernier calipers or vernier count (VC). Least count of the vernier calipers is calculated by

L.C = Value of Smallest Division of MS/Total Number of Divisions on VS

Micrometer Screw Gauge:

A screw gauge is an instrument that is used to measure thickness of a wire, glass, plastic and metal sheets accurately up to 0.01mm. A micrometer screw gauge has two scales, the main scale (MS) and the circular scale (CS). The circular scale rotates over the main scale.

Least Count (LC)

The smallest measurement that can be made with the help of a screw gauge is known as least count of screw gauge. Least count of the screw gauge is calculated by:

L.C = Pitch of the Screw / Total number of divisions of CS

where pitch is the distance between two consecutive threads of the linear screw.

Physical Balance:

A physical balance is an instrument that is used to find the mass of an object. Actually, it is the lever of the first kind with equal arms.

Stop Watch:

A stop watch is an instrument that is used to measure accurately the time interval for any physical event. It can be used to measure the fraction of a second.

Measuring Cylinder:

A measuring cylinder is a glass cylinder of uniform area of cross section with a scale in cubic centimeter or millimeter marked on it. It is used to measure the volume of a liquid.