International system (SI)of units

 The International System of units originally proposed by the Comite International des Poids et Measures (CIPM) and subsequently recommended by the General Conference on Weights and Measures, by the International Standards Organization (ISO) and by the International Electrotechnical Commission (IEC) are commonly known as the SI units (not S.I. unit). It is very essential that all concerned adhere to the style recommended for SI units. It is based on the MKS (Meter-Kilogram-Second) system rather than any variant of rk the CGS (Centimeter-Gram-Second) system. Students of nd engineering should take care while using and writing the SI ty units. The units under International System of units are divided nd into following..

The system for the measurement of fundamental units:

(a)F.P.S. System (Foot-Pound-Second): In which the length, mass and time are measured in feet, pound and seconds Respectively.

(B) C.GS. System (Centimetre-Gram-Second): In which the length, mass and time are measured in centimetre, gram and conds respectively.

(c) M.K.S. System (Metre-Kilogram-Second): In which the length, mass and time are measured in metre, kilogram ands respectively.

(d) M.K.S.A. System (Metre-Kilogram-Second-Ampere): In which the length, mass, time and current are measured in metre, kilogram, seconds and amperes respectively.

Definitions:

1.Matter: A substance which occupies some space, weight and can be felt by one or more senses is called the matter.For example, wood, stone and iron etc.

2.Weight: The weight of a body is the gravitational force with which the earth attracts the body towards its centre. It is not constant at all place of the earth. Its unit is kg in M.K.S. system.

3.Mass: Mass is defined, as the quantity of the matter contained in a body and it is constant in all places. Its unit isk in M.K.S. system.

4.Speed: The rate of change of motion or the rate of change of displacement of a body in any direction is called

5.velocity: Vein The velocity is defined as the rate of displacement of a body in a certain direction. Its unit is km/hrs or m/ sec M.K.S. system.

Speed = Time taken

6. Acceleration: The rate of change of velocity of a body is known as acceleration. Its unit is m/sec² or km/hrs?

 7. Force: Force is something which changes or tends to change the position of a body. Its unit is kg.m/sec² or newton in M.K.S. system.

Force = Mass x Acceleration

8. Momentum: The momentum of an object is the product of its mass and velocity. Its unit is kg.m/sec.

Momentum Mass x Velocity.

Terms and definitions with units related to Electrical:

1. Electromotive force: It is the force which causes the current to flow in the circuit. It is produced by a battery of generator. Its unit is volt and its symbol is "E".

Electromotive force

2. Potential difference: The potential difference is the pressure between any two points in a circuit. It is less than the

E.M.F. Its symbol is "V" and the unit is volt. The instrument which measures the P.D. is called voltmeter. 

3. Current: The flow of electrons is called the current. Its unit is ampere and its symbol is "I". The instrument which measures it is called ampere meter.

4. Volt: It is the unit of E.M.F. and P.D. One volt is that much force which causes the current of one ampere through a resistance of one ohm

Base Units: The units for the base quantities are called base units, which include the following quantities.

Derived Units:   These are units which can be formed by combining base units according to the algebraic expressions linking the corresponding quantities. Many of these expressions can be replaced by special names and symbols and are used to form other derived units.

 

drive Si system

Supplementary Units: The SI units assigned to third

class are called 'supplementary units' which may be regarded either as base units or as derived units.

SI supplementary units

ELECTRICAL SYMBOLS ACCORDING TO BIS

The representation of an object, in a simplest way, on a drawing, is called a symbol. In engineering drawing, commonly used graphical symbols are employed, to denote the name of electrical components and instruments, along with the various accessories used. These symbols must convey the same meaning to everyone who reads the drawing. They are standardised by the Bureau of Indian Standards (BIS) according to internally agreed conventions as adopted by International Electrotechnical Commission. Bureau of Indian Standards (BIS) is the national standards body of India and the statuatory organisation under the Bureau of Indian Standards Act, 1986.

The Bureau is the leader that resolves matters concerned with standardization, certification and quality. It strives for providing efficient timely service and to satisfy the needs of the customers for quality goods.

While working in a technical field, it is advised to constantly refer to the Indian Standard Specification (ISS) to ensure the correctness of a symbol.

Ac DC current

Electric circuit and symbol's

CHOOSE THE CORRECT ANSWER. 

1:What is the unit of resistance ?                        Ans. The unit of resistance is ohm.

2 :What is the unit of current and voltage ?                                                             Ans. The unit of current is ampere and voltage is volt.

3: What is power, what is its unit?                                      Ans. The rate of doing work is called power and its unit is watt.

4:On what factor the work depend ?

Ans. Work = Force x Distance and its unit is Nw-m.

5:What is the unit of energy?

Ans. The unit of energy is Kilo Watt hour      (kWh).

6:What is the formula of specific resistafnce ?

Ans.p = R a/L ohm meter or micro-ohm-cm.

Ques. 7 How much energy will a 1000 watt bulb consume in.                        Ans. A 1000 watt bulb will consume 1unit or one Kilo-Watt-hour

Ques. 8 How is current measured ?

Ans. It is measured by a Ampere meter which is connected in series

Ques.9 .Wthe value of 1 H.P. equivalent to 1 kW.

Ans. 1 H.P. = 0.7355 kW

Ques.12 Write a unit of energy in M.K.S. system

Ans. H.P. (Metric) = 735.5 Jouls/sec or Watts.

Ques.10 Name the different types of energy                               Ans. There are following types of energy:

(a) Heat energy,

(d) Light energy,

(b) Mechanical energy,

(e) Sound energy.