1. Physics is a science of measurements.
2. PHYSICAL QUANTITY: Any quantity which canbe measured directly (or) indirectly (or) in terms of which any laws of physics can be expressd is called physical quantity.
3. There are two types of physical quantities.
1) Fundamental Quantity : Physical Quantities which cannot be expressed in terms of any other physical quantites are called fundamental physical quantities.
E.g. length, mass, time, temperature etc..
2) Derived Quantity :Physical Quantities which are derived from fundamental quantities are called derived quantities.
E.g. Area, density, force etc...
UNIT OF MEASUREMENT:
1. A fixed measurement chosen as a standard of measurement to measure a physical quantity is called a Unit.
2. To measure a physical quantity means to determine the number of times its standard unit contained in that physical quantity.
3. A standard Unit is necessary for the sake of 1. accuracy,2. convenience, 3. unformity and 4. equal justice to all.
4. The standard unit chosen should have the following characteristics.
1. Consistency (or) invariability
2. Availability (or) reproducibility
3. Imperishability (Permanency)
4. Convenience and acceptability
The measure of a Physical Quantity is given by a numerical value and a unit. x= nu where x is the measure of a physical quantity, n is numerical value and u is the unit.
6. The numerical value obtained on measuring a physical quantity is inversely proportional to the magnitude of the unit chosen.
NU = CONSTANT.
Fundamental unit :The unit used to measure the fundamental quantity is called fundamental unit.
e.g., Metre for length, kilogram for mass etc..
Derived unit : The unit used to measure the derived quantity is called derived unit.
e.g., m2 for area, gm cm-3 for density etc...
FUNDAMENTAL QUANTITIES AND THEIR S.I. UNITS:
1. There are seven basic quantities and two supplementary quantities in S. I. system. The names and units with symbols are given below:
2. DEFINITIONS FOR S.I. UNITS:
1. meter: meter is 1 in 299, 792, 458th part of the distance travelled by light in vaccum in 1 second.
2. Kilogram: Kilogram is the mass of a platinum - irridium alloy cylinder proto type kept at Serves, near Paris.
3. second: One second is the time taken by 9,192, 631, 770 cycles of the radiation from the hyperfine transition in ceasium - 133 atom, when unperturbed by external fields.
4. Kelvin: This is 1/273. 16 of the temperature at the triple point of water measured on thermodynamic scale.
5. Candela: Candela is the luminous intensity in a direction normal to the surface of a block body at the temperature of freezing platinum at a pressure of 101, 325 newton per square metre.
6. ampere: ampere is the current which when flowing in each of two parallel conductors of infinite length and negligible cross-section and placed one metre apart in vaccum causes each conductor to experience a force exactly 2x10-7 newton per metre length.
7. mole: mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon - 12.
8. radian: radian is the angle subtended at the centre of a circle by an arc whose length is equal to the radius.
9.Steradian: The solid angle subtended at the centre of the sphere of radius 1 metre by its surface of area 1 square metre. Solid angle= normal area/r2. Total solid angle that can be formed at any point in space or at the centre of a sphere is 4 π steradian.
If you are interested in knowing about errors then here is the link for the Eerrors occur during the measurements of physical quantities.
2. PHYSICAL QUANTITY: Any quantity which canbe measured directly (or) indirectly (or) in terms of which any laws of physics can be expressd is called physical quantity.
3. There are two types of physical quantities.
1) Fundamental Quantity : Physical Quantities which cannot be expressed in terms of any other physical quantites are called fundamental physical quantities.
E.g. length, mass, time, temperature etc..
2) Derived Quantity :Physical Quantities which are derived from fundamental quantities are called derived quantities.
E.g. Area, density, force etc...
UNIT OF MEASUREMENT:
1. A fixed measurement chosen as a standard of measurement to measure a physical quantity is called a Unit.
2. To measure a physical quantity means to determine the number of times its standard unit contained in that physical quantity.
3. A standard Unit is necessary for the sake of 1. accuracy,2. convenience, 3. unformity and 4. equal justice to all.
4. The standard unit chosen should have the following characteristics.
1. Consistency (or) invariability
2. Availability (or) reproducibility
3. Imperishability (Permanency)
4. Convenience and acceptability
The measure of a Physical Quantity is given by a numerical value and a unit. x= nu where x is the measure of a physical quantity, n is numerical value and u is the unit.
6. The numerical value obtained on measuring a physical quantity is inversely proportional to the magnitude of the unit chosen.
NU = CONSTANT.
Fundamental unit :The unit used to measure the fundamental quantity is called fundamental unit.
e.g., Metre for length, kilogram for mass etc..
Derived unit : The unit used to measure the derived quantity is called derived unit.
e.g., m2 for area, gm cm-3 for density etc...
FUNDAMENTAL QUANTITIES AND THEIR S.I. UNITS:
1. There are seven basic quantities and two supplementary quantities in S. I. system. The names and units with symbols are given below:
2. DEFINITIONS FOR S.I. UNITS:1. meter: meter is 1 in 299, 792, 458th part of the distance travelled by light in vaccum in 1 second.
2. Kilogram: Kilogram is the mass of a platinum - irridium alloy cylinder proto type kept at Serves, near Paris.
3. second: One second is the time taken by 9,192, 631, 770 cycles of the radiation from the hyperfine transition in ceasium - 133 atom, when unperturbed by external fields.
4. Kelvin: This is 1/273. 16 of the temperature at the triple point of water measured on thermodynamic scale.
5. Candela: Candela is the luminous intensity in a direction normal to the surface of a block body at the temperature of freezing platinum at a pressure of 101, 325 newton per square metre.
6. ampere: ampere is the current which when flowing in each of two parallel conductors of infinite length and negligible cross-section and placed one metre apart in vaccum causes each conductor to experience a force exactly 2x10-7 newton per metre length.
7. mole: mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon - 12.
8. radian: radian is the angle subtended at the centre of a circle by an arc whose length is equal to the radius.
9.Steradian: The solid angle subtended at the centre of the sphere of radius 1 metre by its surface of area 1 square metre. Solid angle= normal area/r2. Total solid angle that can be formed at any point in space or at the centre of a sphere is 4 π steradian.
If you are interested in knowing about errors then here is the link for the Eerrors occur during the measurements of physical quantities.
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