Electricity Made by :-

Daksh Tomar

There are two types of charges :- Positive charge :- These are made of sub

atomic particle proton. Negative charge :- These are made of

negative sub atomic particle electron.

Types of charges

The S.I. unit of charge is coulomb. An electron posses a negative charge of

1.5 x 10-19. The S.I. unit of one coulomb is equivalent to

the charge containing 6.25 x 10-18.

S.I. unit of charge

Conductors and InsulatorsConductors Insulators These substance

have the property to conduct electricity through them.

These have free or loosely held electrons which helps in conducting electricity.

Example – copper.

These substance have the property to obstruct the flow of electricity.

These do not have free electrons present in them.

Example – Rubber Insulation.

When a small electric charge is placed in the electric field due to another charge, it experiences a force. So, work has to be done on the positive charge to move it against this force of repulsion.

The electric potential is defined as the work done in moving a unit positive charge fro infinity to that point.

Electric potential

The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. The electric potential at any point is defined as the energy required to bring a unit test charge from an infinite distance slowly to that point.It is usually measured in volts.

Potential Difference

A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit.

Voltmeter has a high resistance so that it takes negligible current.

Voltmeter

The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current.

1 ampere = .

Electric Current

An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name.

An ammeter should have a very low resistance so that it may not change the value of current flowing in the circuit.

Ammeter

We know that an electric circuit, as shown in Fig. 12.1, comprises a cell(or a battery), a plug key, electrical component(s), and connecting wires. It is often convenient to draw a schematic diagram, in which different components of the circuit are represented by the symbols conveniently used. Conventional symbols used to represent some of the most commonly used electrical components.

Circuit Diagram

Ohm’s Law explains the relationship between voltage (V or E), current (I) and resistance (R)

Used by electricians, automotive technicians, stereo installers.

According to Ohm’s law : At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its end.

Ohm’s Law

An electron traveling through the wires and loads of the external circuit encounters resistance. Resistance is the hindrance to the flow of charge. For an electron, the journey from terminal to terminal is not a direct route. Rather, it is a zigzag path that results from countless collisions with fixed atoms within the conducting material. The electrons encounter resistance - a hindrance to their movement. 

The S.I. unit of resistance is ohm’s (Ω).

Resistance

i. Length of conductor.ii. Area of cross section of the conductor (or

thickness of the conductor).iii. Nature of the material of the conductor,

andiv. Temperature of conductor.

Factors affecting Resistance

It has been found by experiments that : The resistivity of a given of a given conductor is

directly proportional to its length. The resistivity of a given conductor is inversely

proportionWhere p(rho) is a constant known as resistivity of the material.

The resistivity of a substance is numerically equal to the resistance of a rod of that substance which is 1 meter long and 1 square meter in cross section.

Resistivity, p = . The unit of resistance R is ohm. al to its area of cross section.

Resistivity

Resistors can be combined in two ways –

i. In series.ii. In parallel.

Combination of Resistors

When two (or more) resistors are connected end to end consecutively, they are said to be connected in series.

According to the law of combination of resistance in series: The combined resistance of any number of resistances connected in series is equal to the sum of the individual resistances.

R= R1 +R2 +R3+………..

Resistors in Series

When two (or more) resistors are connected between the same points, they are said to be connected in parallel.

According to the law of combination of resistance in parallel: The reciprocal of the combined resistance of any number of resistances connected in parallel is equal to the sum of the reciprocals of the individual resistances.

1/R= 1/R1 +1/R2 +1/R3+……….. When a number of resistances are connected in

parallel then their combined resistance is less than the smallest individual resistance.

Resistors in Parallel

Parallel and Series connection

Parallel connection Series connection

If one electric appliance stops working due to some defect, then all other appliances keep working normally.

In parallel circuits, each electric appliance has its own switch due to which it can be turned on or off independently.

Each appliance gets same voltage as that of power source.

If one electric appliance stop working due to some defect, then all other appliances stop working.

All the electric appliances have only one switch due to which they cannot be turned on or off separately.

In series circuit, the appliances do not get same voltage (220 V) as that of the power supply line.

In series circuit the overall resistance of the circuit increases due to which the current from the power source is low.

When electricity passes through a high resistance wire like a nichrome wire, the resistance wire becomes very hot and produces heat. This is called the heating effect of current.

Heating effect of electric current

LetAn electric current I is flowing through a resistor having resistance equal to R.The potential difference through the resistor is equal to V.The charge Q flows through the circuit for the time t.Thus, work done in moving of charge Q of potential difference V = VQSince, this charge Q flows through the circuit for time t,

Joule’s law of heating

The heat produced in wire is directly proportional to i. Square of current.ii. Resistance of wire.iii. Time for which current is passed

H = I2 Rt gives the rate at which electric energy is dissipated or consumed in an electric circuit. This is also termed as electric power. The power P is given by

P = VIOr P = I2R = V2/R

The SI unit of electric power is watt (W). It is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V. Thus,

1 W = 1 volt × 1 ampere = 1 V A The unit ‘watt’ is very small. Therefore, in actual practice we use a much larger

unit called ‘kilowatt’. It is equal to 1000 watts. Since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (W h). One watt hour is the energy consumed when 1 watt of power is used for 1 hour. The commercial unit of electric energy is kilowatt hour (kW h), commonly known as ‘unit’.

1 kW h = 1000 watt × 3600 second= 3.6 × 106 watt second

= 3.6 × 106 joule (J)

Electric Energy