Electricity
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ELECTRICITY
A good conductor should have the following properties:-
Electrical properties
• The conductivity must be good.
• Electrical energy spent in the form of heat must be low.
• Resistivity must be low (to reduce voltage drop and by load by loss).
• Increase in resistance with temperature must be low.
Mechanical properties
• Ductility (the property of being drawn into thin wires).
• Solderability: the joint should have minimum contact resistance.
• Resistance to corrosion: should not get rusted when used outdoors.
• Should withstand stress and strain.
• It should be easy to fabricate.
Economical factors
CLASSIFICATION OF CONDUCTORS :-
It is a soft and extremely malleable metal. Even though it is the best conductor, its use is limited because of its high cost.
Copper
It is a very good conductor. It is mealleable and ductile, and also has high resistance to corrosion by liquids. Therefore, it is widely used for wires, cables, overhead conductors, busbars and conducting parts of various electrical appliances.
RESISTANCE WIRES
These are conductors with very high resistance for specific applications like filaments of incandescent lamps, heating
elements etc. The following are a few examples:
1 Tungsten 2 Nichrome 3 Eureka
4 German silver 5 Manganin 6 Platinum
7 Mercury 8 Carbon 9 Brass.
The resistance values of the metallic resistances will increase with increase in temperature.
INSULATORS :-
These are the materials which offer very high resistance to these flow of current and make current flow very negligible or nil. These materials have very high resistance usually of many megohms (1 megohm = 106 ohms) per centimetre cube. The insulators should also posseses high dielectric strength. This means that the insulating material should not break down or puncture even on application of a high voltage (or high electrical pressure) to a given thickness.
PROPERTIES OF INSULATORS :-
ELECTRICITY
Electricity is a type of energy that cannot be seen with the eyes, but its effects are known by its presence. Electrons pass through the wires through the electrical conductive material. The conductors act as medium in transporting the material from one place to another.
In today's modern era, the use of electricity has become excessive and every little work is also being done through electricity. Even if we look around us, the use of electricity will be seen more. Electricity is used in
1.HEAT : - Heat can be generated with the help of electricity. Such as heaters, electric furnaces, welding, soldering, iron, presses, electric cookers etc.
2. LIGHTING:- Bulb flashlight tubelight, fancy light, motor, vehicle light etc.
3. POWER:- Rail, tram, electric motor, big machines like planer or shaper etc. are run with the help of electricity.
4. SOUND:-
telephone, telegraphy, television, radio, loudspeaker etc.
OTHER:-
electroplating, battery, charging, X-ray rays, ultraviolet rays, cathode rays, electro photocopy machine, scanner machine computer system etc.
Electricity is being used in communication, telecommunications, entertainment, education, light production, medicine, operation of machines, banks etc.
ATOMIC STRUCTURE :-
All substances are made up of many microscopic particles. The smallest particle in which the properties of matter are present is called molecule. All particles of the same substance are similar in size and properties. Each molecule has the same physical and chemical properties as the original substance. The molecule can also be divided into parts. The smallest particle in which the properties of the original substance do not exist, participate in chemical activity. It is called an atom.
The atom has three fundamental particles.
Proton neutrons and electrons.
1. Proton - The central part of an atom is called the nucleus. Protons and neutrons are located in the nucleus itself. A proton is a positively charged particle. The mass of a proton is 1845 times the mass of the electron.
2. Neutron: - It also remains in the nucleus, the central part of the atom, but it has no charge unlike proton. Its mass is equal to the mass of the proton. The total mass of an atom's nucleus is contained in its protons and neutrons.
3. Electron: - It is a negatively charged moving particle. Its mass is equal to 1 / 1840th of the mass of one atom of hydrogen. Each atom orbits a fixed number of electrons in different orbits around the nucleus.An electron has a charge of 1.6 × 10 ^ -19 couloms with negative charge.
The outer orbitals of the atom of most metals have one or two electron deficiencies (called holes) or excess. When the electron is deficient, the atom gets charged due to the arrival of electron in the outer orbit of the atom and in the last orbit, one, two or more electrons called free electrons, the atom is positively charged.
CONDUCTOR :-
Some materials and metals readily allow passage for electric current to flow. In such materials, called conductors, electrons are able to pass readily from atom to atom.
PROPERTIES OF CONDUCTORS :-
All substances are made up of many microscopic particles. The smallest particle in which the properties of matter are present is called molecule. All particles of the same substance are similar in size and properties. Each molecule has the same physical and chemical properties as the original substance. The molecule can also be divided into parts. The smallest particle in which the properties of the original substance do not exist, participate in chemical activity. It is called an atom.
The atom has three fundamental particles.
Proton neutrons and electrons.
1. Proton - The central part of an atom is called the nucleus. Protons and neutrons are located in the nucleus itself. A proton is a positively charged particle. The mass of a proton is 1845 times the mass of the electron.
2. Neutron: - It also remains in the nucleus, the central part of the atom, but it has no charge unlike proton. Its mass is equal to the mass of the proton. The total mass of an atom's nucleus is contained in its protons and neutrons.
3. Electron: - It is a negatively charged moving particle. Its mass is equal to 1 / 1840th of the mass of one atom of hydrogen. Each atom orbits a fixed number of electrons in different orbits around the nucleus.An electron has a charge of 1.6 × 10 ^ -19 couloms with negative charge.
The outer orbitals of the atom of most metals have one or two electron deficiencies (called holes) or excess. When the electron is deficient, the atom gets charged due to the arrival of electron in the outer orbit of the atom and in the last orbit, one, two or more electrons called free electrons, the atom is positively charged.
CONDUCTOR :-
Some materials and metals readily allow passage for electric current to flow. In such materials, called conductors, electrons are able to pass readily from atom to atom.
PROPERTIES OF CONDUCTORS :-
A good conductor should have the following properties:-
Electrical properties
• The conductivity must be good.
• Electrical energy spent in the form of heat must be low.
• Resistivity must be low (to reduce voltage drop and by load by loss).
• Increase in resistance with temperature must be low.
Mechanical properties
• Ductility (the property of being drawn into thin wires).
• Solderability: the joint should have minimum contact resistance.
• Resistance to corrosion: should not get rusted when used outdoors.
• Should withstand stress and strain.
• It should be easy to fabricate.
Economical factors
• Low cost.
• Easy availability.
• Easy to manufacture.
• Easy availability.
• Easy to manufacture.
CLASSIFICATION OF CONDUCTORS :-
1. Metallic
2. Liquid
3. gaseous
Metallic Electrolytic Gaseous
The best conductors are metallic. The commonly used conductors in electrical appliances and machines are described here under.
Silver
Silver
It is a soft and extremely malleable metal. Even though it is the best conductor, its use is limited because of its high cost.
Copper
It is a very good conductor. It is mealleable and ductile, and also has high resistance to corrosion by liquids. Therefore, it is widely used for wires, cables, overhead conductors, busbars and conducting parts of various electrical appliances.
Aluminium
It is a metal light in weight. It is also ductile, malleable and a good conductor of electricity. Nouwadays, it is more widely used (since it is cheaper than copper) for wires and cables. All aluminium conductors (AAC) and aluminium conductors (steel reinforced) (ACSR) are used in overhead and transmission lines. (More details on copper and aluminium are furnished under the topic ‘non-ferrous metals and alloys as applicable to electrical trades’).
It is a metal light in weight. It is also ductile, malleable and a good conductor of electricity. Nouwadays, it is more widely used (since it is cheaper than copper) for wires and cables. All aluminium conductors (AAC) and aluminium conductors (steel reinforced) (ACSR) are used in overhead and transmission lines. (More details on copper and aluminium are furnished under the topic ‘non-ferrous metals and alloys as applicable to electrical trades’).
RESISTANCE WIRES
These are conductors with very high resistance for specific applications like filaments of incandescent lamps, heating
elements etc. The following are a few examples:
1 Tungsten 2 Nichrome 3 Eureka
4 German silver 5 Manganin 6 Platinum
7 Mercury 8 Carbon 9 Brass.
The resistance values of the metallic resistances will increase with increase in temperature.
SEMICONDUCTORS :-
Such substances which are neither good conductors nor bad cunning, but by mixing of some impurities become partial conductors, are called semi-conductors. Such as silicon and germanium.
INSULATORS :-
These are the materials which offer very high resistance to these flow of current and make current flow very negligible or nil. These materials have very high resistance usually of many megohms (1 megohm = 106 ohms) per centimetre cube. The insulators should also posseses high dielectric strength. This means that the insulating material should not break down or puncture even on application of a high voltage (or high electrical pressure) to a given thickness.
PROPERTIES OF INSULATORS :-
1. Easily folded to any size.
2. The effect of weather and temperature should be minimized.
3. Its resistance should be high.
4. The dielectric strength must be high. 5. Should be cheap and easy to get in price.
CLASSIFICATION OF INSULATING MATERIALS:-
1. Solid insulators
2. Liquid insulators
3. Gas insulators
ELECTRIC CURRENT:-
The flow of electrons in a conductor is called electric current. It is obtained by the flow of electrons in a closed circuit. The unit of electric current is ampere. It is represented by I . This is a scalar quantity. The electrons flow from the negative terminal to the positive terminal.
In the second sense, electric current is the rate of charge flow, ie the amount of charge that flows in a conductor in 1 second is called electric current. In a conductor, if q is the total charge current in t seconds.
Electric current I = q / t
STATIC ELECTRICITY:-
If we rub the glass rod in silk and then bring it near small pieces of paper, then it attracts the pieces of paper to itself. In this way, if two special types of substances are rubbed together, then the ability to attract other small objects arises in them. we call this static electricity. We cannot carry this power from one place to another nor do any useful work.
The same electric charges push each other away and the opposing charges attract each other.
DYNAMIC ELECTRICITY:-
The flow of electrons is called electric current. This power can be brought from one place to another with the help of conductor. We can generate this type of electricity with the help of cell, generator etc.
SPEED OF ELECTRIC CURRENT:-
The speed of electric current is the same as the speed of light i.e. 3 × 10 ^ 8 m / s.
TYPES OF ELECTRIC CURRENT :-
1. Direct current or D.C.
2. Alternating current or A.C.
1. DIRECT CURRENT OR D.C. :-
The value and direction of this type of electric current remain unchanged. It has two terminals called positive terminal and negative terminal. The current always flows from positive to negative end. D.C power we can get from DC cell, battery or DC generator.
2. ALTERNATING CURRENT OR A.C. :-
The value and direction of this type of electric current are constantly changing. Its terminal is called phase and neutral. The electric current flows from the phase towards the neutral. Our homes supply 50 Hz current. The current starts from zero and attains the highest positive value, then again attains the zero value and after receiving the negative highest value in the other direction, again attains the zero value. This is called a cycle. A.C. We can get electricity from an AC generator or alternator.
COMPARISON BETWEEN A.C. AND D.C. :-
ALTERNATING CURRENT :-
1. It is generated in the ranges of 6,600 V, 11000 V and 33,000 V.
2. Voltage can be stepped up or stepped down by using transformer.
3. Transmission cost is less.
4. Less maintenance
5. Power up to 5,00,000 kw can be generated in a single alternator.
6. AC generator can run at high speeds. So, speed control is not easy.
7. Slip rings and brushes are used to collect the current.
DIRECT CURRENT :-
1. It is generated up to 6,600 V only.
2. Voltage steeped up or down not possible.
3. Cost High.
4. High maintenance.
5. Power up to 10,000 kw can be generated in a single generator.
6. It can’t run at high speeds. Speed control is easy.
7. commutator and brushes are used to collect the current.ADVANTAGES OF A.C. :-
1. In transmission there is saving in copper wire.
2. Since there is no spark in A.C. machine there is no interference in Radio sound.
3. This can be produced to maximum voltage i.e. 33000 volts.
4. Voltage can be dropped or raised with the help of transformers.
5. Its mechanism is simple and cheap.
6. Output is more due to availability of more than one phase.
DISADVANTAGES OF A.C.:-
1. A single phase motor is not self-starter.
2. Due to thin wire in A.C., the voltage drop is more.
3. It cannot be used for electroplating and in charging secondary cells.
4. The speed of motors run by it is difficult to change.
5. There is danger to security due to high voltage.
AMPERE :-
Ampere is a unit of electric current. In a closed circuit, the current flowing through a voltage of 1 volt with one ohm resistance is 1 ampere or the amount of electric current that flows into a silver nitrate solution collects 0. 000118 grams of silver in one second. So there will be 1 ampere.
ELECTRO - MOTIVE FORCE :-
The force that conducts an electric current from one end of a conductor to another is called an electric motive force. Its unit is volt. The electric motive force is represented by E.
ELECTRIC VOLTAGE :-
The force that causes electrons to flow in a circuit is called electrical voltage. Its unit is volt. It is represented by V. The voltage is divided into the following classes -
1. Low voltage - 0 volt to 250 volt
2. Medium voltage - 250 volt to 650 volt
3. High voltage - 650 volt to 11000 volt
4. Extra High voltage - above 11000 volt
POTENTIAL DIFFERENCE:-
The potential or voltage between any two points in a closed circuit is called the potential difference. Its unit is volt and it is also called PD. This is represented by V.
ONE VOLT :-
When a 1 ampere current flows through a conductor with a one ohm resistance, the value of the potential difference at the ends of the conductor is 1 volt.
RESISTANCE :-
It is the property of a substance to oppose to the flow of electric current through it, is called resistance.
Symbol: R,
Unit : Ohm Ω
Ohm meter is used to measure the resistance.
SPECIFIC RESISTANCE :-
The specific resistance of a material is the resistance offered to a current it passed between the opposite faces of the unit cube of the material. Specific resistance is measured in Ohm- m or micro ohm - cm.
Each mateiral has its own specific resistance or resistivity.
E.g. : Copper - 1.72 Ohm-cm, Silver - 1.64 ohm- cm,
Eureka - 38.5 ohm- cm, Iron - 9.8 ohm- cm,
Aluminium - 2.8 ohm-cm
R ∝ L/A
R = ⍴ . L/A
⍴ = R. A / L
R = Resistance in ohms
L = Length of the conductor in cm
r = Specific Resistance in ohm cm
(symbol pronounced as rho)
A = Area of cross - section in cm^2.
OHM'S LAW :-
Scientist GS Ohm established a relation between electric current resistance and voltage, which is called Ohm's law.
According to this rule, the current flowing in a closed circuit is proportional to the potential difference present in that circuit. When temperature and all physical conditions are stable and inversely proportional to the resistance.
V ∝ I . I ∝ 1 / R
V = I R R= Resistance in ohm
I = V / R I = current in ampere
R = V / I v = voltage in volt
SERIES CONNECTION :-
The total resistance is equal to the sum of all the resistances.
In a series connection the end of the first load is connected to the beginning of the second load and all loads are connecting end to end.
Features of series connection:-
• The same current flows through all the loads.
• The voltage across each load is proportional to the resistance of the load.
• The sum of the voltages across each load is equal to the applied voltage.
• The Total resistance is equal to the sum of all the resistances.
I = I1 = I2
V = V1+ V2 + ...
R = R1 + R2 + ...
Example:-
Three resistances of 3 ohms, 9 ohms and 5 ohms are connected in series. Find their resultant resistance.
Sol.
R = R1 + R2 + R3
= 3 + 9 + 5
Total resistance = 17 Ω
PARALLEL CONNECTION :-
In a parallel connection the beginning and the ends of the loads are connected together.
Features of parallel connection:-
• The current flowing through each load depends upon the resistance of the load.
• The voltage across each load is the same and is equal to the voltage applied to the circuit.
• The total resistance of a parallel connection is always
smaller than the smallest resistance in the circuit.
• In parallel connection the reciprocal of the total
resistance is equal to the sum of the reciprocals of all
resistances in the circuit.
I = I1 + I2 + ...
V = V1 = V2
1/R = 1 / R1 + 1 / R2 + ......
Example :-
Determine the total resistance or total current supply if three resistances of 4 ohms, 8 ohms and 16 ohms are connected in parallel with 12 volt supply.
Sol.
Total resistance
1 / R = 1 / R1 + 1 / R2+1 / R3
1 / R = 1 / 4 + 1 / 8 + 1 / 16
= 4+2+1 = 7 Ω
16 16
R = 16/7 Ω. Answer
V = IR
I = V/R = 12 = 5 .25 ampere
16/7 Answer
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