The process of electrolysis is used in depositing a layer of one metal over other. The process of depositing a layer of one metal over the surface of another metal by passing electric current in called electroplating.

Electroplating of metals is done to protect the metals from corrosion and for decoration purpose. For example, the vessels of iron are electroplated with copper or silver or gold to make it attractive and to protect from rusting.

Electroplating of an Iron Object with Copper Metal
To deposit a layer of copper metal on an iron object, take a glass jar and fill it with copper sulphate solution (electrolyte). Connect the plate of copper metal to the positive terminal (anode) of battery and iron object to the negative terminal (cathode) of the battery. Now, dip these two electrodes in the solution of copper sulphate. When electric current is passed through the CuSO₄ solution, you will find that a thin layer of copper metal is deposited on the cathode (iron object) and an equivalent amount of copper is lost by the anode (copper plate) and is dissolved into the solution.

Test Your Understanding and Answer These Questions:

1. What is electroplating process?
2. Explain the process of electroplating of an iron object with copper metal?

You have already learnt that there are certain chemical reactions which produce electricity. But, it is interesting to note that when electric current is passed through certain liquids a chemical reaction takes place. This is called chemical effect of electric current. For example, when an electric current is passed through acidified water, it splits up to form hydrogen and oxygen gas. Let’s understand the chemical effect of current more deeply by discussing various terms and laws related with it.

Electrolytes
The substances which allow electricity to pass through them when dissolved in water or in molten state and dissociate into ions on passing the current through them are called electrolytes. For example, solution of sodium chloride in water and solution of copper sulphate in water are electrolytes.

Electrolysis
 The process of dissociation of an electrolyte into ions on passing the electric current through it is called electrolysis. For example, when an electric current in passed through aqueous solution of sodium chloride it splits up into positively charged sodium ions and negatively charged chloride ions.

                          NaCl          Na⁺      +      Cl^–

Remember that the vessel in which the process of electrolysis is carried is called voltameter.

Test Your Understanding and Answer These Questions:

1. What is chemical effect of electric current?
2. What do you meant by electrolytes? Give examples.
3. What is electrolysis process? Give an example.
4. What do you understand by voltameter?

 When an electric current is passed through a conductor, the conductor becomes hot after some time and produce heat. This happens due to the conversion of some electric energy passing through the conductor into heat energy. This effect of electric current is called heating effect of current.

The heating effect of current was studied experimentally by Joule in 1941. After doing his experiments Joule came to the conclusion that the heat produced in a conductor is directly proportional to the product of square of current (I²), resistance of the conductor (R) and the time (t) for which current is passed. Thus,

              H          I²Rt

Derivation of Formula
To calculate the heat produced in a conductor, consider current I is flowing through a conductor AB of resistance R for time t. also consider that the potential difference applied across its two ends is V.

Now, total amount of work done in moving a charge q from point A to B is given by:

W     =     q     X     V    (1)

Now, we know that charge = current × time

or        q     =     I     X     t

and      V     =     I     X     R (Ohm’s law)

Putting the values of q and V in equation (1), we get

W     =     (I   X   t)    X    (I   X   R)

Or       W     =     I²Rt

Now, assuming that all the work done is converted into heat energy we can replace symbol of ‘work done’ with that of ‘heat produced’. So,

H     =     I²RT

Applications of Heating Effect of Current
The heating effect of current is used in various electrical heating appliances such as electric bulb, electric iron, room heaters, geysers, electric fuse etc.

Examples of Heating Effect of Electric Current

   

Test Your Understanding and Answer These Questions:

1. What is heating effect of electric current?
2. Derive the formula for heating effect of electric current.
3. What are applications of heating effect of electric current?

The electric energy consumed by an electrical appliance is given by the product of its power and the time for which it is used i.e.

                 Electrical energy    =    Power X time

                 or,                  E    =    P X t

The S.I. unit of electrical energy is 1 joule

1 Joule
One joule is the amount of electrical energy consumed when an electrical appliance of 1 watt power is used for one second, i.e.

                 1 Joule    =    1 watt   X   1 second

               or     1 J    =    1 w   X   1 s

               or     1 J    =    1ws

Commercial Unit of Energy: – Kilowatt Hour
One kilowatt hour is the total electrical energy consumed when an electrical appliance having a power of 1 Kilowatt is used for 1 hour. It is written as kWh in short form.

Relationship between Kilowatt Hour and joule

                 1 kWh    =    1 kilowatt   X   1 hour

           so   1 kWh    =    (1000w)   X   (60 X 60 sec.)

                               = 3600000 watt seconds

           or   1 kWh     =    3.6   X   10⁶ J

Test Your Understanding and Answer These Questions:

1. What is electric energy?
2. What is 1 joule?
3. What is commercial unit of energy?
4. Define 1 kilowatt hour.
5. What is the relationship between kilowatt hour and joule?

 The rate at which electrical work is done by an electrical appliance is called electric power, i.e.

                 Power    =    

                        P    =    

              but,    W    =    VIt

              So       P    =    

              So       P    =    VI watt    (1)

    Where,    V   =    potential difference (in volt)

                   I    =    current (in ampere)

Therefore,    P =   potential difference (in volt)   X   current (in ampere)

Also we know that according to Ohm’s law V   =   I R

Putting the value of I in equation (1), we get

                        P    =    IR   X   I
              or       P    =    I²R

The S.I.unit of power is watt. It is denoted by the letter W.

1Watt
The power is said to be of 1 watt if 1 joule of work is done in 1 second. Thus,

                        1 watt    =    

The S.I. unit of power represents a small amount of power and therefore it is inconvenient to use it where a large amount of power is involved. So, for commercial purposes a bigger unit of electric power called kilowatt is used.

                        1 kilowatt    =    1000 watt
              or       1 KW          =    1000 W

Test Your Understanding and Answer These Questions:

1. What is electric power?
2. What is definition of 1 watt?
3. What is definition of kilowatt?

When two or more resistors are connected across a common point so that same current flows through different paths they are said to be connected in parallel. Suppose three resistors R₁, R₂ and R₃ are joined in parallel as shown in figure and let the potential difference applied across point A and B be V.

Let I be the current reaching point A from the battery and I₁, I₂ and I₃ be the current passing through resistors R₁, R₂ and R₃ respectively. Here it is clear that total current:

              I    =    I₁    +    I₂    +    I₃   (1)

According to Ohm’s law

              V   =    I₁R₁    =    I₂R₂    =    I₃R₃

    or       I₁    =    ,    I₂   =       and   I₃ =    

If R_p is the resultant resistance of the parallel circuit, then

              V    =    IR_p

    or       I    =    

By putting the values of I, I₁, I₂ and I₃ in equation (1), we get

              

    or       

       So, when the resistors are joined in parallel the reciprocal of total resistance of a number of resistors is equal to the sum total of the reciprocal of all the individual resistors.

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Test Your Understanding and Answer These Questions:

1. What is Parallel circuit?

 The resistors can be combined in two ways to get the desired resistance.

    (1) Series Circuit (combination of resistors in series)

(2) Parallel Circuit (Combination of resistors in parallel)

When two or more resistances are connected end to end so that same current flows through each resistor they are said to be connected in series. Suppose three resistors R₁, R₂ and R₃ are joined in series as shown in figure and let the current passing through them be I.

Let V₁, V₂ and V₃ be the potential difference across each resistor respectively. According to ohm’s law:

              V₁    =    I R₁
V₂    =    I R₂
and     V₃    =    I R₃

If V is the total potential difference between the ends A and D, then

V    =    V₁    +    V₂    +    V₃
or       V    =    I R₁  +    I R₂  +    I R₃

If R_s is the resultant resistance of series circuit, then

V     =    IR_s
or       IR_s   =    I R₁ +  I R₂ + I R₃
or       IR_s   =    I(R₁ +  R₂ + R₃)
or       R_s    =    R₁ + R₂ + R₃

So, when some resistors are joined in series, the total resistance of given series of resistors is equal to the sum total of individual resistors.

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Test Your Understanding and Answer These Questions:

1. What is series circuit?

According to ohm’s law the current (I) flowing through a conductor is directly proportional to the potential difference (V) across the ends of the conductor, provided temperature of the conductor is kept constant, i.e.

                 I        V

       or      V         I

       or      V    =    R    X    I

     Where R is constant and is called resistance.

Resistance of a Conductor

The resistance of a conductor is the property of a conductor to oppose the flow of current passing through it. The resistance of a conductor may be defined as the ratio of potential difference (V) across the ends of the conductor to the current (I) flowing through it, i.e.

               Resistance    =    

                   or       R    =    

The S.I. unit of a resistance is ohm. It is represented by the symbol omega (Ω)

1 ohm (Ω)
1 ohm is the resistance of a conductor through which a current of 1 ampere flows when a potential difference of 1 volt is applied across its ends ; e.g.

               1 Ohm    =    

Factors Affecting the Resistance of a Conductor

The various factors that affect the resistance of a conductor are:

1. Length of the Conductor
The resistance of a conductor is directly proportional to the length of the conductor, i.e.

                 R        l

Therefore the resistance of the conductor becomes double it the length of a conductor is doubled, and the resistance of the conductor becomes half if the length of a conductor is halved.

2. Area of Cross Section of the Conductor
The resistance of a conductor is inversely proportional to area of cross-section of the conductor, i.e.

                 R        

Therefore the resistance of the conductor becomes half when the area of cross-section of a wire is doubled, and the resistance of the conductor becomes double when the area of cross-section of wire is halved. This means that a thick wire has less resistance than a thin wire.

3. Nature of Material of the Conductor
The resistance of a conductor depends on the nature of the material of which it is made.

4. Effect of Temperature
The value resistance of a conductor increases on raising the temperature and decreases on lowering the temperature.

Question:- Why electrician wear rubber hand gloves while working with electricity? Answer:- Electrician wear rubber hand gloves while working with electricity because rubber is bad conductor of electricity and protects them from electric shocks.

Specific Resistance or Resistivity

       We know that                 R        I     (1)

       and                                R             (2)

       By combining both equation we get

                                            R        

       or                                  R    =    ρ    X         (3)

Where ρ (rho) is a constant and is know as specific resistance or resistivity.

              By re-arranging equation (3) we get

                                            ρ    =    R    X         (4)

       if A = 1m² and l = 1m then from equation (4), we get

                                            ρ    =    R

Thus the specific resistance or resistivity of a conductor is resistance of a conductor which is 1 meter long and 1 square meter in cross section. S.I. Unit of specific resistance or resistivity is ohm-m or Ω-m.

Test Your Understanding and Answer These Questions:

1. What is ohm’s law?
2. What is definition of resistance?
3. What is specific resistance?
4. What is S.I. unit of specific resistance?
5. What is S.I. unit of resistance of a conductor?
6. What are the factors effecting resistance of a conductor?
7. Why electrician wear rubber hand gloves while working with electricity?

Electric Circuit
It is a closed circuit consisting of wires and resistors along which electrons flow very rapidly when connected between the terminals of a battery. Electric circuit is represented by drawing circuit diagram.

Circuit Diagram
A diagram which shows the actual arrangement of different components in an electric circuit is called a circuit diagram.

In a circuit diagram the actual arrangement of different components of electric circuit is shown by using electrical symbols. The various electrical symbols used in circuit diagrams can be shown as:

Test Your Understanding and Answer These Questions:

1. What is electric circuit?
2. What is circuit diagram?
3. Write some electric symbol used in a circuit diagram.

The reason of current flow in a metallic wire is the flow of free electrons present in it. When a metallic wire is not connected to a source of electricity the electrons present in it are free to move in all directions. As a result, there is no net flow of current in the wire.

But, if the metallic wire is connected to a source of electricity, the electrons present in wire start to move from negative terminal to positive terminal. This flow of electrons in the wire from negative terminal to positive terminal is responsible for current flow inside a wire

Test Your Understanding and Answer These Questions:

1. How does current flow inside a wire?