Electricity is a kind of energy. Electricity is obtained by conversion of other forms of energy like heat energy, chemical energy, nuclear energy, mechanical energy and energy stored in water etc.
Sources of Electricity
Battery: Battery stores electrical energy in the form of chemical energy and it gives power when required. Battery is used in automobiles and electronics, etc.,
Generator: It is a machine which converts the mechanical energy into electrical energy.
Thermo couple: If two dissimilar pieces of metals are twisted together and its joined end is heated in a flame, then a potential difference or voltage will be induced across the ends of the wires. Such a device is known as a Thermo couple. Thermo couple is used to measure very high temperature of furnaces.
Types of Electric Current
Direct current (DC): In DC the direction and magnitude of the current does not change. The steady current flow will be from the positive terminal to the negative terminal. DC Sources: Cells, batteries and DC generators.
Alternating current (AC): In AC both the direction and magnitude of the current will be changing at definite intervals of time. The current flow will be from the phase terminal to the Neutral terminal.
Quantity of Electricity
The strength of the current in any conductor is equal to the quantity of electrical charge that flows across any section of it in one second. If ‘Q’ is the charge and ‘t’ is the time taken then,
$\displaystyle \small I=\frac{Q}{t}$
$\displaystyle \small Q=I\times t$
Coulomb
In an electric circuit if one Ampere of current passes in one second, then it is called one coulomb. Its smaller unit is ampere second (As). Its larger unit is ampere hour (Ah).
1 Ah = 3600 As (or) 3600 coulomb
Electro Motive Force (EMF)
It is the force which causes the flow of free electrons in any closed circuit due to difference in electrical pressure or potential. It is represented by ‘E.’ Its unit is Volt.
Potential Difference (P.D)
This is the difference in electrical potential measured across two points of the circuit. Potential difference is always less than EMF. The supply voltage is called potential difference. It is represented by V.
Current
The flow of electrons in any conductor is called current. It is represented by I and its unit is Ampere. Ammeter is used to measure the current by connecting series with the circuit.
Resistance
The property of a substance to oppose the flow of electric current through it is called resistance. Symbol: R, Unit : Ohm (Ω), Ohm meter is used to measure the resistance.
Laws of Resistance
The resistance offered by conductor depends on the following factors.
1. The resistance of the conductor is directly proportional to the length of the conductor
$\displaystyle \small R\propto L$
2. The resistance of the conductor is inversely proportional to its cross sectional area.
$\displaystyle \small R\propto \frac{1}{A}$
$\displaystyle \small R=\rho \frac{L}{A}$
Types of Electrical Materials According to the Electricity Law
Conductors
$\displaystyle \small \bullet$ Substances through which flow of current (flow of free electrons) can be set up easily are called conductors.
$\displaystyle \small \bullet$ The number of free electrons present in the substance decide its conductivity.
$\displaystyle \small \bullet$ The conductors which allow the electricity to pass easily are called good conductors and those allow with difficulty are called bad conductors.
$\displaystyle \small \bullet$ Classification:
$\displaystyle \small \circ$ Metallic
$\displaystyle \small \circ$ Liquid
$\displaystyle \small \circ$ Gaseous
Insulators
$\displaystyle \small \bullet$ Insulators are the materials which offer very high resistance that they practically allow no electricity to flow through them.
$\displaystyle \small \bullet$ Classification
$\displaystyle \small \circ$ Solid insulators: wood, asbestos, cotton, bitumen, mica, adhesive tape, Bakelite, rubber, vulcanised rubber, glass etc.
$\displaystyle \small \circ$ Liquid insulators: mineral oils, resins, synthetic liquids, varnishes etc.
$\displaystyle \small \circ$ Gas insulators: dry air, hydrogen, nitrogen, inert gases etc.
Semiconductors
$\displaystyle \small \bullet$ Substances which are neither good conductors nor good insulators are called semiconductors.
$\displaystyle \small \bullet$ Number of free electrons is low in comparison to that in conductors, hence their resistance is high.
$\displaystyle \small \bullet$ Good medium for the control of electric current.
$\displaystyle \small \bullet$ Used for making diodes, transistors etc.
$\displaystyle \small \bullet$ Ex: germanium silicon, carbon, boron etc.
Ohm’s Law
Ohm’s law states that, “if all the physical conditions (temperature, length, cross-sectional area) are same, then the current through a conductor between two points is directly proportional to the potential difference across the two points.
$\displaystyle \small I\propto V$
$\displaystyle \small I=\frac{1}{R}V$
$\displaystyle \small R=\frac{V}{I}$
where,
V= voltage between two points of conductors in Volts.
I = current through the conductor in Ampere.
R = resistance in Ohms.
Specific Resistance/Resistivity
$\displaystyle \small \bullet$ Specific resistance is a measure of the potential electrical resistance of a conductive material.
$\displaystyle \small R=\rho \frac{l}{A}$
where,
R = resistance of a conductor
l = length of a conductor
A = cross-sectional area of conductor
$\displaystyle \small \rho$ = specific resistance (constant)
$\displaystyle \small \bullet$ Unit is ohm-m, ohm-cm
Temperature Coefficient ($\displaystyle \small \alpha$)
$\displaystyle \small \bullet$ Temperature coefficient of resistance is defined as the ratio of increase in resistance per degree rise of temperature to the original resistance.
$\displaystyle \small \alpha=\frac{R_{t}-R_{0}}{R_{0}t}$
where,
$\displaystyle \small R_{0}$ = resistance of conductor at $\displaystyle \small 0^{0}C$
$\displaystyle \small R_{t}$ = resistance of conductor at $\displaystyle \small t^{0}C$
$\displaystyle \small \alpha$ = temperature coefficient of resistance
Series and Parallel Connections of Resistance
Resistances may be connected in series or parallel or in series-parallel combinations.
Series connection
$\displaystyle \small \bullet$ In a series connection the end of the first load is connected to the beginning of the second load and all loads are connected end to end. The total resistance is equal to the sum of all the resistances.
$\displaystyle \small V=V_{1}+V_{2}+V_{3}$
$\displaystyle \small R=R_{1}+R_{2}+R_{3}$
where,
$\displaystyle \small R_{1}, R_{2}, R_{3}$ = resistances connected in series
$\displaystyle \small V_{1}, V_{2}, V_{3}$ = voltage drop across $\displaystyle \small R_{1}, R_{2}, R_{3}$ respectively
$\displaystyle \small \bullet$ Current remains the same in each resistance and line.
$\displaystyle \small \bullet$ Voltage is divided across the resistances. Total voltage across resistances will be equal to applied voltage.
Parallel connection
$\displaystyle \small \bullet$ In a parallel connection the beginning and the ends of the loads are connected together.
$\displaystyle \small I=I_{1}+I_{2}+I_{3}$
$\displaystyle \small \frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}$
where,
$\displaystyle \small R_{1}, R_{2}, R_{3}$ = resistances connected in series
$\displaystyle \small I_{1}, I_{2}, I_{3}$ = current in $\displaystyle \small R_{1}, R_{2}, R_{3}$ respectively
$\displaystyle \small \bullet$ Voltage remains same in each branch.
$\displaystyle \small \bullet$ Current is divided among the resistances.
Electrical Power
$\displaystyle \small \bullet$ Power is the rate of doing work.
$\displaystyle \small \bullet$ The product of voltage and current is also known as electric power.
$\displaystyle \small P=VI=\frac{V^{2}}{R}=I^{2}R$
$\displaystyle \small \bullet$ Generally the power of electric machine is represented by Horse Power.
$\displaystyle \small \bullet$ Horse Power is the practical unit of electrical power, its value in metric system is 735.5 Watt and in British system is 746 Watt.
$\displaystyle \small \circ$ 1 kWatt = 1.3596 HP (metric)
$\displaystyle \small \circ$ 1 kWatt = 1.3404 HP (British)
Electrical Work/Energy
$\displaystyle \small \bullet$ Electrical work or energy is the product of electrical power and time.
$\displaystyle \small W=P\times t$
1 Wh = 3600 Watt sec.
1 Kwh = 1000 Wh = 3600000 Watt sec
Magnetic Induction
When a magnet is brought near to an iron bar, a magnetism is produced in the iron bar. The phenomenon is known as magnetic induction.
Intensity of Magnetic Field
The force acting on a unit pole placed in a magnetic field is called the intensity of magnetic field. It is denoted by letter H and its unit is Wb/m.
Faraday’s Laws of Elctromagnetic Induction
Faraday’s first law states that whenever the magnetic flux is linked with a circuit changes, an emf is always induced in it.
Faraday’s second law states that the magnitude of the induced emf is equal to the rate of change of flux linkage.
Types of emf
Dynamically induced emf: The induced emf is due to the movement of the conductor in a stationary magnetic field OR by the movement of the magnetic field on a stationary conductor.
If the conductor moves with a relative velocity ‘v’ with respect to the field, then the induced emf will be
$\displaystyle \small e=BLV\sin \theta$ Volts
where
B = magnetic flux density, measured in tesla
L = effective length of the conductor in the field in metres
V = relative velocity between field and conductor in metre/second
θ = the angle at which the conductor cuts the magnetic field
Statically induced emf: The induced emf is due to change of flux linkage over a stationary conductor.
Sources of Electricity
Battery: Battery stores electrical energy in the form of chemical energy and it gives power when required. Battery is used in automobiles and electronics, etc.,
Generator: It is a machine which converts the mechanical energy into electrical energy.
Thermo couple: If two dissimilar pieces of metals are twisted together and its joined end is heated in a flame, then a potential difference or voltage will be induced across the ends of the wires. Such a device is known as a Thermo couple. Thermo couple is used to measure very high temperature of furnaces.
Types of Electric Current
Direct current (DC): In DC the direction and magnitude of the current does not change. The steady current flow will be from the positive terminal to the negative terminal. DC Sources: Cells, batteries and DC generators.
Alternating current (AC): In AC both the direction and magnitude of the current will be changing at definite intervals of time. The current flow will be from the phase terminal to the Neutral terminal.
Quantity of Electricity
The strength of the current in any conductor is equal to the quantity of electrical charge that flows across any section of it in one second. If ‘Q’ is the charge and ‘t’ is the time taken then,
$\displaystyle \small I=\frac{Q}{t}$
$\displaystyle \small Q=I\times t$
Coulomb
In an electric circuit if one Ampere of current passes in one second, then it is called one coulomb. Its smaller unit is ampere second (As). Its larger unit is ampere hour (Ah).
1 Ah = 3600 As (or) 3600 coulomb
Electro Motive Force (EMF)
It is the force which causes the flow of free electrons in any closed circuit due to difference in electrical pressure or potential. It is represented by ‘E.’ Its unit is Volt.
Potential Difference (P.D)
This is the difference in electrical potential measured across two points of the circuit. Potential difference is always less than EMF. The supply voltage is called potential difference. It is represented by V.
Current
The flow of electrons in any conductor is called current. It is represented by I and its unit is Ampere. Ammeter is used to measure the current by connecting series with the circuit.
Resistance
The property of a substance to oppose the flow of electric current through it is called resistance. Symbol: R, Unit : Ohm (Ω), Ohm meter is used to measure the resistance.
Laws of Resistance
The resistance offered by conductor depends on the following factors.
1. The resistance of the conductor is directly proportional to the length of the conductor
$\displaystyle \small R\propto L$
2. The resistance of the conductor is inversely proportional to its cross sectional area.
$\displaystyle \small R\propto \frac{1}{A}$
$\displaystyle \small R=\rho \frac{L}{A}$
Types of Electrical Materials According to the Electricity Law
Conductors
$\displaystyle \small \bullet$ Substances through which flow of current (flow of free electrons) can be set up easily are called conductors.
$\displaystyle \small \bullet$ The number of free electrons present in the substance decide its conductivity.
$\displaystyle \small \bullet$ The conductors which allow the electricity to pass easily are called good conductors and those allow with difficulty are called bad conductors.
$\displaystyle \small \bullet$ Classification:
$\displaystyle \small \circ$ Metallic
$\displaystyle \small \circ$ Liquid
$\displaystyle \small \circ$ Gaseous
| Conductor | Uses |
|---|---|
| Silver | In sensitive measuring instruments, tiny capacitors, C.B. points etc. |
| Copper | In electric wires and cables, winding wire, transformer choke, motor, generator etc. |
| Brass | In electrical accessories |
| Aluminium | In electric wires and cables, winding wire, capacitors, shielding etc. |
| Iron | In telephone wire, chassis and body of equipment |
| Lead | In underground cables, solder |
| Tin | In solder and anticorrosive plating on various metals |
| Zinc | In Lechlanche and dry cells and in galvanizing irons sheets, wires etc. |
| Eureka | In resistors |
| Nichrome | In heating elements |
| Tungsten | In bulbs, thermionic tubes etc. |
| Carbon | In resistors, brushes of electric machine electrode etc. |
Insulators
$\displaystyle \small \bullet$ Insulators are the materials which offer very high resistance that they practically allow no electricity to flow through them.
$\displaystyle \small \bullet$ Classification
$\displaystyle \small \circ$ Solid insulators: wood, asbestos, cotton, bitumen, mica, adhesive tape, Bakelite, rubber, vulcanised rubber, glass etc.
$\displaystyle \small \circ$ Liquid insulators: mineral oils, resins, synthetic liquids, varnishes etc.
$\displaystyle \small \circ$ Gas insulators: dry air, hydrogen, nitrogen, inert gases etc.
Semiconductors
$\displaystyle \small \bullet$ Substances which are neither good conductors nor good insulators are called semiconductors.
$\displaystyle \small \bullet$ Number of free electrons is low in comparison to that in conductors, hence their resistance is high.
$\displaystyle \small \bullet$ Good medium for the control of electric current.
$\displaystyle \small \bullet$ Used for making diodes, transistors etc.
$\displaystyle \small \bullet$ Ex: germanium silicon, carbon, boron etc.
Ohm’s Law
Ohm’s law states that, “if all the physical conditions (temperature, length, cross-sectional area) are same, then the current through a conductor between two points is directly proportional to the potential difference across the two points.
$\displaystyle \small I\propto V$
$\displaystyle \small I=\frac{1}{R}V$
$\displaystyle \small R=\frac{V}{I}$
where,
V= voltage between two points of conductors in Volts.
I = current through the conductor in Ampere.
R = resistance in Ohms.
Specific Resistance/Resistivity
$\displaystyle \small \bullet$ Specific resistance is a measure of the potential electrical resistance of a conductive material.
$\displaystyle \small R=\rho \frac{l}{A}$
where,
R = resistance of a conductor
l = length of a conductor
A = cross-sectional area of conductor
$\displaystyle \small \rho$ = specific resistance (constant)
$\displaystyle \small \bullet$ Unit is ohm-m, ohm-cm
Temperature Coefficient ($\displaystyle \small \alpha$)
$\displaystyle \small \bullet$ Temperature coefficient of resistance is defined as the ratio of increase in resistance per degree rise of temperature to the original resistance.
$\displaystyle \small \alpha=\frac{R_{t}-R_{0}}{R_{0}t}$
where,
$\displaystyle \small R_{0}$ = resistance of conductor at $\displaystyle \small 0^{0}C$
$\displaystyle \small R_{t}$ = resistance of conductor at $\displaystyle \small t^{0}C$
$\displaystyle \small \alpha$ = temperature coefficient of resistance
Series and Parallel Connections of Resistance
Resistances may be connected in series or parallel or in series-parallel combinations.
Series connection
$\displaystyle \small \bullet$ In a series connection the end of the first load is connected to the beginning of the second load and all loads are connected end to end. The total resistance is equal to the sum of all the resistances.
$\displaystyle \small V=V_{1}+V_{2}+V_{3}$
$\displaystyle \small R=R_{1}+R_{2}+R_{3}$
where,
$\displaystyle \small R_{1}, R_{2}, R_{3}$ = resistances connected in series
$\displaystyle \small V_{1}, V_{2}, V_{3}$ = voltage drop across $\displaystyle \small R_{1}, R_{2}, R_{3}$ respectively
$\displaystyle \small \bullet$ Current remains the same in each resistance and line.
$\displaystyle \small \bullet$ Voltage is divided across the resistances. Total voltage across resistances will be equal to applied voltage.
Parallel connection
$\displaystyle \small \bullet$ In a parallel connection the beginning and the ends of the loads are connected together.
$\displaystyle \small I=I_{1}+I_{2}+I_{3}$
$\displaystyle \small \frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}$
where,
$\displaystyle \small R_{1}, R_{2}, R_{3}$ = resistances connected in series
$\displaystyle \small I_{1}, I_{2}, I_{3}$ = current in $\displaystyle \small R_{1}, R_{2}, R_{3}$ respectively
$\displaystyle \small \bullet$ Voltage remains same in each branch.
$\displaystyle \small \bullet$ Current is divided among the resistances.
Electrical Power
$\displaystyle \small \bullet$ Power is the rate of doing work.
$\displaystyle \small \bullet$ The product of voltage and current is also known as electric power.
$\displaystyle \small P=VI=\frac{V^{2}}{R}=I^{2}R$
$\displaystyle \small \bullet$ Generally the power of electric machine is represented by Horse Power.
$\displaystyle \small \bullet$ Horse Power is the practical unit of electrical power, its value in metric system is 735.5 Watt and in British system is 746 Watt.
$\displaystyle \small \circ$ 1 kWatt = 1.3596 HP (metric)
$\displaystyle \small \circ$ 1 kWatt = 1.3404 HP (British)
Electrical Work/Energy
$\displaystyle \small \bullet$ Electrical work or energy is the product of electrical power and time.
$\displaystyle \small W=P\times t$
1 Wh = 3600 Watt sec.
1 Kwh = 1000 Wh = 3600000 Watt sec
Magnetic Induction
When a magnet is brought near to an iron bar, a magnetism is produced in the iron bar. The phenomenon is known as magnetic induction.
Intensity of Magnetic Field
The force acting on a unit pole placed in a magnetic field is called the intensity of magnetic field. It is denoted by letter H and its unit is Wb/m.
Faraday’s Laws of Elctromagnetic Induction
Faraday’s first law states that whenever the magnetic flux is linked with a circuit changes, an emf is always induced in it.
Faraday’s second law states that the magnitude of the induced emf is equal to the rate of change of flux linkage.
Types of emf
Dynamically induced emf: The induced emf is due to the movement of the conductor in a stationary magnetic field OR by the movement of the magnetic field on a stationary conductor.
If the conductor moves with a relative velocity ‘v’ with respect to the field, then the induced emf will be
$\displaystyle \small e=BLV\sin \theta$ Volts
where
B = magnetic flux density, measured in tesla
L = effective length of the conductor in the field in metres
V = relative velocity between field and conductor in metre/second
θ = the angle at which the conductor cuts the magnetic field
Statically induced emf: The induced emf is due to change of flux linkage over a stationary conductor.
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