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Note on Electricity

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Static Electricity

Charged particles:

The charge is developed in nonmetals like plastic, wool, nylon, polyester, ebonite, etc. in insulating materials due to friction. These materials when rubbed against each other develop the charge. When we put off cyclic or polyester dress, we hear the clicking sound due to the transfer of charges. The dress materials get charged due to the friction of the body.

Electric Cells

A cell is a device where a potential difference between two conductors is maintained by a conversion of chemical energy into electrical energy. A cell consists of two metal rods called electrodes dipped in a solution called electrolyte.

When the cell is in pen circuit, the potential difference between electrodes is called its electromotive force (e. m. f). The strength of the cumulative e.m.f., which a cell can produce in a given circuit, depends on the e.m.f. The e.m.f of cells depend on

  1. materials of its electrodes.
  2. the nature of its electrolyte.

Simple cell

This cell was invented by Alessandro Volta in 1800. It consists of two plates, one copper and other of zinc, both are dipped in dilute sulphuric acid taken in the glass container. When two plates are connected by, a copper wire provided with a bulb in between, the bulb glows showing the flow of electric current. The copper and zinc plates are called the electrodes of the cell. Zinc is the negative electrode as it supplies the electron and copper is the positive electrode. Dilute sulphuric acid is the electrolyte. The electron current flows from zinc to copper. The potential difference between the terminals of the cell is 1.08V. Therefore, it is not suitable for use in devices like torches, calculators, transistors, etc.

The reaction inside the cell can be shown as

Zn → Zn+ + 2e-
H2SO4 → 2H+ + SO4--
2H + +2e- → H2
Zn + H2SO4 → ZnSO4 + H2

Defects of simple cell

We cannot draw current for a long time as this cell has defects. There are two types of defects in the voltaic cell. These are:

  1. Polarization
  2. Local action

Polarization

It is caused by the deposition of the hydrogen gas on the surface of the copper plate in the form of small bubbles. They prevent the hydrogen ions from reaching the copper plate and thus the current given by the cell, decreases gradually. Polarization stops functioning of the cell. Polarization can be avoided by brushing off the hydrogen bubbles or by putting a chemical called potassium dichromate in acid. Potassium dichromate oxide changes hydrogen to water.

Local action

The combined zinc used in the cell contains certain impurities like carbon, iron, etc. Because of this local current is set up between zinc and these impurities in addition to the main current. These local currents cannot be utilized and thus constitute wastage of energy. Local action reduces the life of the cell. Amalgamating is the coating of zinc plate with mercury. Mercury covers these impurities present in the zinc plate. Local action can be avoided by amalgamating the surface of the zinc plate.

Dry cell

It was invented by Laclanche Georges in 1865. A dry cell is made without using the liquid. It consists of a zinc container, which also serves as the negative terminal. The electrolyte is a paste of ammonium chloride. A carbon rod with a brass cap serves as the positive electrode. It is surrounded by a mixture of powdered manganese dioxide and carbon particles.

Hydrogen is formed in the chemical reaction that takes place in the cell. The manganese dioxide reacts with the hydrogen formed and prevents it from collecting on the zinc electrode. In this way, the presence of manganese dioxide prevents the polarization. A porous seal at the top prevents the chemicals from dying out. The cell is dry from outside, but the chemicals are wet. The local action cannot be removed completely so it may decrease the life of the cell.

The electrons flow in a wire connecting the two terminals from the zinc to the carbon electrode. The dry cell, being compact, light and portable, is very convenient to use. Dry cells cannot be charged and reused and therefore they are called primary cells. Cells used in vehicles for lighting purposes or as anemergency light in our home called lead-acid cell. They can be charged and used again. Therefore, these cells are called secondary cells.

The action of the cell can be described as follows:

Zn → Zn++ + 2e-
2NH4Cl → 2NH3 + 2H+ + 2Cl-
2N++ + 2Cl- → ZnCl2
Zn + 2NH4Cl → 2NH3 + ZnCl2+ 2H+ + 2e-
The electrons so released are collected by zinc rod making it as negative potential with respect to the electrolyte.
The ammonia gas (NH3) so produced escapes and hydrogen ions react with manganese dioxide (MnO2) as follows the forming water.
H+ + MnO2 → MnO3 + H2O+ 2e++

Thus, the positive charge is transferred to the carbon rod, which gains positive potentials with respect to the electrolyte.

Advantages of dry cell over simple cell

  1. The electrolyte is in the form of the paste. They do not contain liquid; therefore, it is easier to carry from one place to another place.
  2. They are compact.
  3. They are cheaper than other cells.

Connection of cells

In our daily life, we use more than two cells for different purposes. These cells are connected for use and this arrangement is called combination or connection of cells.

Cells in series:

When a number of cells are connected in series, the negative pole of one cell is connected to the positive pole of the cells and so on. When the internal resistance the cells are connected in series, to get the maximum current.


Cells in parallel combination:

When a number of cells are connected in parallel, all the positive poles are connected to one point and all the negative poles are connected to the other. When the external resistance is negligible in comparison to the internal resistance, the cells are connected in parallel so as to keep the current constant.

  • Charge is developed in nonmetals like plastic, wool, nylon, polyester, ebonite, etc. in insulating materials due to friction.
  • Electric Cell: A cell is a device where a potential difference between two conductors is maintained by a conversion of chemical energy into electrical energy.
  • Types of defects in voltaic cell: Polarization, Local action
  • Connection of cells: Cells in parallel combination, Cells in series combination
.

Very Short Questions

The continuous flow of electrons is called electricity. It is of two types:

  • Static electricity
  • Current electricity

The electricity in which the electric charges do not flow or remain at rest is called static electricity. The charged produced on the comb, glass rod, etc. are the examples of it. The electricity in which the electric charges flow is called current electricity. Eg: current through the copper wire, etc.

When we rub a comb on our hair, then electrons of the atoms of the hair are transformed to the comb so that comb becomes negatively charged. When this comb is brought near to the pieces of paper, positive charges accumulate at the edge of the paper, as opposite charges attract. Now, comb starts to attract pieces of paper.

Charges are produced through friction between any two dry materials. Whether a body gets positively charged or negatively, it depends upon the nature of the body.

Nylon or acrylic clothes get charged due to friction with the body for the whole day. While taking off these clothes, transfer of charges take place and crackling sound with sparks is produced.

The sources through which electricity can be generated are the sources of electricity. Examples:

  • Cell
  • Dynamo/generator
  • Photo cell, etc.

A cell is a device that converts chemical energy into electrical energy.

A simple cell is a cell having two metallic plates dipped in an acid solution to generate electricity.

Electrodes are the metal rods which are dipped in acid solution in a cell.
An electrolyte is a solution which splits into its constituent ions when electricity is passed.

Electrode with the negative terminal is known as anode whereas electrode with the positive terminal is called cathode.

The two defects of a simple cell are:

  1. Polarization
  2. Local action

During chemical reaction in a cell, hydrogen gas is produced and it accumulates, it is known as polarization.
It can be removed by using depolarizer like manganese dioxide, potassium dichromate, etc.

Zinc plate used in the simple cell is not pure so impurities present in it provides a conducting path for the flow of charge. This makes the zinc wasted. It is called the local action.
It can be removed by using pure zinc or amalgamated zinc rod.

Local action reduces the life of the cell.

The simple cell is not used to produce current for a long time because of the defects like polarization and local action.

A cell which has paste or powder chemicals and converts chemical energy into electrical energy is known as dry cell.

Simple cell Dry cell
It has liquid chemicals filled in a vessel. It has dry chemicals.
Zinc plate is negative terminal and copper plate is positive terminal. Carbon rod is positive and zinc can is negative.

Simple cell has liquid chemicals and it is difficult to carry from one place to another. Dry cell has no solution. So, it is easier to carry it from one place to another and there is no risk of spilling acid from the dry cell. So, dry cell is more useful than simple cell in our daily life.

Cells are widely used in torch-lights, radio, telephone, electric bells, etc.

It is easier to handle as it does not contain liquid solution

  • It is compact
  • It is cheaper than simple cell

MnO2 is used as depolarizer in a dry cell. When the hydrogen gas is produced and accumulated, then MnO2 reacts with the gas and does not let the hydrogen gas to accumulate at a place. i.e. 2MnO2+ H2 → Mn2O3+ H2O

The conducting path of the electricity where cell, wire, switch and load are connected is called an electric circuit. An open circuit is a circuit in which the current is not flowing or switch is off.
A closed circuit is a circuit in which the current flows or switch is on.

The process of arranging two or more than two cells in a circuit is called the combination of cells.
Its types are:

  • Parallel combination
  • Series combination

If the positive terminals of two or more cells are joined together at a point and all the negative terminals are joined at another common point, then this combination is called the parallel combination of cells.
It's one advantage is:

  • It works for a long period of time.

Its one disadvantage is:

  • In parallel combination, whatever be the increase in the number of cells, the brightness of the bulb will not increase.

If the positive terminal of the first cell is connected to the negative terminal of the second cell and the positive terminal of the second cell is connected to the negative terminal of the third cell and so on, then it is known as the series combination of cells.
It's one advantage is:

  • The brightness of the bulb increases with the increase  in number of cells and vice versa

Its one disadvantage is:

  • It works for a short time

Series combination of cells Parallel combination of cells
If the positive terminal of the first cell is connected to the negative terminal of the second cell and the positive terminal of the second cell is connected to the negative terminal of the third cell and so on, then it is known as the series combination of cells. If the positive terminals of two or more cells are joined together at a point and all the negative terminals are joined at another common point, then this combination is called the parallel combination of cells.
The bulb glows with more brightness. The bulb glows with less brightness.
The bulb glows for a shorter time The bulb glows for a longer time.

0%
  • The unit of current is ______ .

    volt
    ampere
    watt
    columb
  • When there is an electric current passing through a wire, the particles moving are ______ .

    electrons
    neutrons
    protons
    atoms
  • What happens when an electric switch is turned off?

    The circuit is broken
    The circuit becomes series circuit
    There is a short circuit
    none of these
  • A circuit that has only one path for electric flow is ______.

    series circuit


    parallel circuit


    both series and parallel circuit


    battery circuit


  • When the external resistance is negligible in comparison to the internal resistance, the cells are connected in ______ so as keep the current constant.

    mixed combination
    none of these
    series combination
    parallel combination
  • In series circuit, which of the following quantity remains same throughout the circuit ______.

    Current


    Current and Voltage


    none of these


    Voltage


  • Which one of the following is portable cell?

    mixed cell
    simple cell
    dry cell
    dynamo cell
  • The electricity in which electric charge remain in motion is called ______.

    current electricity


    alternating current


    direct current


    static electricity


  • Which one of the following is not source of electricity?

    bulb
    dynamo cell
    cell
    photocelll
  • Depolarizer in dry cell is ______ .

    HCl
    MnO2
    NH4Cl
    H2SO4
  • When a glass rod is rubbed with silk, the charge developed in it is ______.

    neutral


    positive


    both positive and negative


    negative


  • You scored /11


    Take test again

DISCUSSIONS ABOUT THIS NOTE

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Rohit Kumar Ganesh

Electrical devices are used to talk in the space, why?


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why are eletrical device use to talk device in space?


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Arya Godar

Why have the poles of a magnet strong attracting capacity?


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