Current Electricity

Front 1

Electric current

Back 1

The net flow of charge through a metallic wire constitute an electric current

SI unit is Ampere

Front 2

Current Electricity

Back 2

The branch of physics which deals with the study of charges in motion is called current electricity.

Front 3

Current carriers

Back 3

The charged particles whose flow is in a definite direction constitute the electric current are called current carriers.

Front 4

Current carriers in solid conductors , liquids and gases

Back 4

Valence electrons are the current carriers in solid conductors. In liquids ions are the charge carriers. Positive ions and electrons are the current carriers in gases.

Front 5

Measure of electric current

Back 5

The time rate of flow of charge through any cross section of a conductor

Front 6

Define 1 ampere

Back 6

The current through a wire is it be one ampere if one coulomb of charge is flowing per second through any section of the wire.

Front 7

Direction of current

Back 7

The direction of flow of positive charge gives the direction of current. This is called conventional current. The direction of flow of electrons gives the direction of electronic current. The direction of electronic current is opposite to that of conventional current.

Front 8

Current is a vector or scalar quantity ?

Back 8

Current is scalar quantity.

Front 9

Ohms law

Back 9

Ohm's laws states that the current flowing through a conductor is directly proposional to the potential difference across the ends of the conductor provided the physical conditions of the conductor such as temperature,mechanical strain etc are kept constant

Front 10

Electrical resistance

Back 10

It is the obstruction posed by the conductor to the flow of electric current through it.

Electrical resistance is defined as the ratio of the potential difference V across the ends of the conductor to the current I flowing through it.

SI unit of resistance is ohm

Front 11

Define 1 ohm

Back 11

One ohm is the resistance of a conductor through which current of 1 ampere flows when a potential difference of one volt is applied across the ends of the conductor

Front 12

Cause of resistance of a conductor

Back 12

Resistance of a given conducting wire arises on account of frequent collision of free electrons with the ions or atoms of the conductor while drifting towards the positive end the conductor which in turn depends upon the arrangement of atoms in the conducting material

Front 13

Factors on which resistance depends

Back 13

1. Directly proportional to length of the conductor l

2. Inversely proportional to area of cross section A

3. Also depends on nature of material

4. Temperature of the conductor

Front 14

Resistivity or specific resistance

Back 14

Specific resistance of the material of a conductor is defined as the resistance of unit length with unit area of cross section of the material of the conductor.

SI unit of resistivity is ohm metre

Front 15

Factors on which resistivity depends

Back 15

Resistivity depends on nature of material and temperature

Front 16

Conductance (G)

Back 16

The inverse of resistance is called conductance of a conductor unit of conductance is ohm raised minus 1 or mho or siemen(s)

Front 17

Electrical conductivity

Back 17

The inverse of resistivity of a conductor is called as electrical conductivity.

Front 18

Current density

Back 18

It is defined as the amount of current flowing per unit area of a conductor around that point provided the area is held in a direction normal to the current

Karan and cities a vector quantity it's direction is the direction of motion of positive charge

Unit of current density is ampere per metre square

Front 19

Drift velocity

Back 19

It is defined as the average velocity with which the free electrons get drifted towards the positive end of the conductor under the influence of an external electric field applied

Front 20

Average relaxation time

Back 20

The average time there as elapsed since each electron suffered its last collision with ion or atom

Front 21

Mobility

Back 21

It is defined as the magnitude of drift velocity of charge per unit electric field applied

Front 22

Effect of temperature on resistance

Back 22

When the temperature of metal conductor is reached the ions or atoms of the metal vibrate with great amblitude and greater frequencies about their mean position . Due to increase in thermal energy the frequency of collision of free electrons with atoms or ions increases

This reduces the relaxation time to Z

But the number density of electrons in metal conductor does not change appreciable with temperature hence the value of electrical resistance R increases with rise of temperature

Front 23

Temperature coefficient of resistance

Back 23

It is defined as the increase in resistance per unit original resistance per degree Celsius or Kelvin rise of temperature

Front 24

Temperature coefficient in metals, insulators and semiconductors

Back 24

For metals like silver copper etcetera Alpha is positive

For insulators and semiconductors Alpha is negative

that is resistance decrease with rise and temperature

Front 25

Why are alloys used to make standard resistance

Back 25

For magnanin. nichrome constantan etc the value of Alpha is very small. Due to high resistivity and low temperature coefficient of resistance these alloys are used in making standard resistance coil

Front 26

Non ohmic devices

Back 26

Those devices which do not away ohm's law are called non ohmic devices

Example vacuum tubes semiconductor diode liquid electrolyte transistor etc

Front 27

Characteristics of non-ohmic devices

Back 27

1. The relation between V and I are non linear

2. The relation between V and I depends on the sign of V

3. The relation between V and I is not unique. ie there is more than one value of V for the same current

Front 28

Commercially produced resistors for domestic use or in lab

Back 28

1. Wirebound resistors

2. Carbon resistors

Front 29

Wire bound resistors

Back 29

They are made by winding the wires of an alloy namely magnanin. these wires are typically in the range of a fraction of an ohm to a few 100 ohms

Front 30

Carbon resistors

Back 30

Karbonn resistors are compact in expensive and the find extensive use in electronics circuits. They are small in size.

The resistors have asset of coaxial colour drinks on them. The first to bonds from the end indicate the first two significant figures of the resistance in ohms. the third bond indicate that decimal multiplier. The last bond stands for tolerance or possible variation in percentage about the indicated values. Ifthe last band is absent tolerance is 20%

Front 31

Heating effect of current

Back 31

According to joules heating effect the amount of heat produced in a conductor is directly proportional to

1. Square of magnitude of current

2. Resistance of a conductor R

3.Time for which current flows t

Front 32

Electric power

Back 32

The rate at which electric work is done by the source of EMF in maintaining the current in an electric circuit is called electric power of a circuit

SI unit of power is 1 watt

Front 33

Define 1 watt

Back 33

The power of an electric circuit is said to be one watt if 1 ampere current place in its against potential difference of one volt. Commercial or practical unit of power is horsepower

Front 34

Electric energy

Back 34

The total electric work done or energy supplied by the source of EMF in maintaining the current in an electric circuit for a given time is called electric energy consumed in a circuit

The commercial unit of electric energy is kilowatthour or unit

Front 35

Electric iron, Electric Heater and Heating rod

Back 35

Electric iron electric heater and heating rod are some of the important household electric appliance based on the heating effect of electric current. the heating element use is nichrome. it is used because

1. It has high specific resistance

2. It's melting point is high

3. It can be easily drawn into wires

4. It is not oxidized easily when heated in air

Electric iron electric heater and heating wrote our high power instruments for given voltage p is proportional to I that is higher the power of the electric appliance larger is the current drawn by it larger is the heat produced since H is proportional to I square

Resistance of high electric power instrument is smaller than that of low electric power

Front 36

Incandescent electric lamp

Back 36

It consists of a metal filament of fine wire of tungsten enclosed in a glass bulb with some inert gas at suitable pressure. The metal element used must be a very high melting point about 3000. When voltage is applied across the bulb the current is passed through the filament. The filament gets heated to very high temperature. It then becomes white hot and then starts anything white light at once

Front 37

Fuse wire

Back 37

It is a safety device generally prepared from tin lead alloy. It should have high resistivity low melting point and suitable current rating corresponding to the load in the circuit

Refuse wire is used in series with the electrical appliances and protect them from strong current

Front 38

Efficiency of an electrical device

Back 38

Efficiency of an electrical device is defined as the ratio of the output power to the input power

Front 39

EMF or electromotive force

Back 39

EMF of a cell is the maximum potential difference between two electrodes of a cell when no current is drawn from the cell

Front 40

Internal resistance

Back 40

Internal resistance of a cell is defined as a resistance offered by the electrolyte and electrodes of a cell when the electric current flows through it

Front 41

Factors on which internal resistance depends on

Back 41

1. Distance between the electrodes

2. Nature concentration and temperature of electrolyte

3. Nature of the electrodes

4. Area of electrodes immersed in electrolyte

Front 42

Terminal potential difference of a cell

Back 42

It is defined as a potential difference between the two electrodes of a cell in a closed circuit

Front 43

Kirchhoff's First law or junction law or current law

Back 43

It state the algebraic some of the current meeting at the junction in a close to circuit is zero

Kirchhoff's first law supports the law of conservation of charge

Front 44

Kirchhoff second law or loop Law or voltage law

Back 44

It stays that algebraic sum of charges in potential around any closed path of electric circuit involving resistance and cells in the loop is zero

Front 45

Wheatstone metre bridge principle

Back 45

It says that if 4 resistance is pqr and s are arranged from upgrades with a cell and key in the battery arm and a galvanometer and the taping key in the galvanometer arm on closing keys if galvanometer shows no deflection the bridge is balanced