ELECTRICITY, Class X, Part- II

     

ACCORDING TO THE CBSE SYLLABUS 2025-26, THIS CHAPTER HAS BEEN RENUMBERED AS CHAPTER 11.

CBSE CLASS 10 SCIENCE CHAPTER 12 ELECTRICITY NOTES-(PART II)

NOTES OF CH 12 ELECTRICITY, CLASS 10TH SCIENCE

 Study Material and Notes of Ch 12 Electricity Class 10th Science

Remaining Topics of this Chapter

5. OHM'S LAW
A. MATHEMATICAL EXPRESSION FOR OHM'S LAW
B. V-I GRAPH FOR OHM'S LAW
C. RESISTANCE
D. OHM
E. RHEOSTAT

6. FACTORS ON WHICH THE RESISTANCE OF A CONDUCTOR DEPENDS
A. RESISTIVITY

7. RESISTORS IN SERIES
A. TOTAL/RESULTANT/OVERALL/EFFECTIVE RESISTANCE IN SERIES
B. VOLTAGE ACROSS EACH RESISTOR

8. RESISTORS IN PARALLEL

9. ADVANTAGE OF PARALLEL COMBINATION OVER SERIES COMBINATION

10. HEATING EFFECT OF ELECTRIC CIRCUIT
A. JOULE'S LAW HEATING EFFECT OF ELECTRIC CURRENT
B. THE FILAMENT OF AN ELECTRIC BULB IS MADE UP OF TUNGSTEN
C. ELECTRIC FUSE
D. ELECTRIC POWER

RESISTANCE AND OHM’S LAW

OHM’S LAW

The current flowing through an ohmic conductor is directly proportional to the applied potential difference between the two ends of the conductor. Ohm’s Law states the relationship between the potential difference across a conductor and the current through it.

MATHEMATICAL EXPRESSION FOR OHM’S LAW

V ∝ I
⇒ V = IR
R is a constant called resistance for a given metal.

V-I GRAPH FOR OHM’S LAW

RESISTANCE (R): 

It is the property of a conductor to resist the flow of charges through it.

 THE S.I. UNIT OF RESISTANCE IS OHM (Ω): .

If the potential difference V is 1 volt and the current I is 1 ampere, then the resistance R’ becomes 1 ohm.

V / I = R

1 Volt / I ampere = 1 ohm
When the potential difference is 1 V and the current through the circuit is 1 A, then the resistance is 1 ohm.

RHEOSTAT:

Variable resistance is a component used to regulate current without changing the source of voltage.

Resistance is a measure of the opposition offered to the current flow in an electric circuit. Resistance is measured in ohms. All materials resist current flow up to some degree. All materials fall into one of two broad categories: Conductors and Insulators.

 R=ρl/A

FACTORS AFFECTING THE RESISTANCE OF A CONDUCTOR

The resistance of a conductor depends on.

1. Length of the conductor.

2. Area of cross-section of the conductor or thickness of the conductor. 

3.  Nature of the material of the conductor.

4. Temperature of the conductor.  

 1. LENGTH OF THE CONDUCTOR

It has been found by experiment that one increasing the length of a wire its resistance increases, and on decreasing the length of the wire is decreased, its resistance decreases. The resistance of a conductor is directly proportional to its length.

R  ᾲ L

The long wire (conductor)has more resistance, and the short wire (conductor) has less resistance.                                                                    

2. EFFECT OF AREA OF CROSS-SECTION OF THE CONDUCTOR.

The resistance of a conductor is inversely proportional to its area of cross-section.

R  ᾲ 1/A

When the area of cross-section of a wire is doubled, its resistance gets halved, and if the area of cross-section of the wire is halved, then its resistance will get doubled. The resistance of the wire is affected by. 

1. A short length of a thick wire is used to get low resistance.

2. long length of a thin wire is used to get high resistance.

3. EFFECT OF THE NATURE OF THE MATERIAL OF THE CONDUCTOR

The electric resistance of a conductor (wire) depends on the nature of the material of which it is made. Some material has low resistance, whereas other has high resistance. For example, if we take two similar wires, having equal length and diameter of copper metal and nichrome wire, about 60 times more than that of copper wire. 

4. EFFECT OF TEMPERATURE

The resistance of all pure metals increases on raising the temperature and decreases on lowering the temperature. 

RESISTIVITY (ρ): 

It is defined as the resistance offered by a cube of a material of side 1m when current flows perpendicular to its opposite faces.

Its S.I. unit is ohm-metre (Ωm).

a. Resistivity does not change with a change in length or area of cross-section, but it changes with a change in temperature.

b. The range of resistivity of metals and alloys is 10^-8 to 10^-6 Ωm.

c. The range of resistivity of insulators is 10¹² to 10¹⁷ Ωm.

d. The resistivity of an alloy is generally higher than that of its constituent metals.

e. Alloys do not oxidize (burn) readily at high temperatures, so they are commonly used in electrical heating devices.

f. Copper and aluminium are used for electrical transmission lines as they have low

resistivity.

 ρ = R A /L

RESISTIVITY (ρ) RHO

 It is a constant as the resistivity of the material of the conductor. Resistivity is also known as specific resistance. It is clear that for a given conductor having specified length L and area of cross-section A, the resistance R is directly proportional to its resistivity ρ. (If we change the material of a conductor to one whose resistivity is two times, then the resistance will also become two times.) The resistance of a given conductor is directly proportional to its length. The resistance of a given conductor is inversely proportional to its area of cross-section.

                                              R  ᾲ L -------------------------------(I)

                                              R  ᾲ 1/A -------------------------- (II)

By taking equations (I) and (II)

                                              R  ᾲ L / A

                                              R  = ƿ L/A

 Or                                        ƿ  = R × A / L

The constant is known as specific resistivity or resistivity ρ.

Where,

R = Resistance of the conductor

A = Area of cross-section of the conductor.

L = Length of the conductor

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

The S.I. Unit of Resistivity is Ohm-meter (Ω m).

 The resistivity of a substance does not depend on its length or thickness. It depends on the nature of the substance and temperature. The resistivity of the alloy is much higher than that of the pure metals (from which they are made).

1.    Nichrome has very high resistivity, due to which the heating element made of nichrome has a high resistance and produces a lot of heat when current is applied.   

2.  Nichrome does not undergo oxidation (or burn) easily at high temperatures. Due to this, nichrome wire can be kept red–hot without burning or breaking in air.

ELECTRIC CIRCUIT AND CIRCUIT DIAGRAM

A closed-loop path through which a current takes is called an electric circuit.

The representation of an electric circuit through symbols is called a circuit diagram.

BATTERY AND ITS WORKING

A cell is a source of potential difference, which is created inside it due to internal chemical reactions.

At anode:                                  Cu(s)⇌Cu2+(aq)+2e−
At cathode:                                 Ag(aq)+2e−⇌2Ag(s)
A combination of cells is called a battery.

ELECTRICITY

All the conductors (like metals) have some electrons that are loosely held by the nuclei of their atoms. These electrons are called “free electrons” and can move from one atom to another. Throughout the conductors. The free electrons or the presence of free electrons in a substance make it a conductor (electricity).

Electricity can be classified into two parts
1.    Static electricity
2.    Current electricity

CONDUCTORS AND INSULATORS

All the substances can be divided mainly into two electrical categories, conductors and insulators.

CONDUCTORS

Those substances through which electric charges can flow are called conductors or Those substances through which electricity can flow easily are called conductors.
Example:- all metals like silver, copper, and aluminium, etc. The metal alloys such as nichrome, Maganin, and constantan.
Metal alloys are also used in making heating elements of electrical appliances, such as nichrome, magnanin, and constantan. In alloys, electrical conductivity is much less than that of pure metals.
Carbon in the form of graphite is also a conductor. The human body, plant (green), and animal body a fairly good conductors. All the metals (Silver, Copper, Aluminium) are good conductors.

INSULATORS

Those substances through which electric charges can’t flow are called insulators (Or) those substances through which electricity can’t flow are called insulators. 

The electrons present in insulators are strongly held by the nuclei of their atoms, since there are no free electrons in an insulator that can move from one atom to another. An insulator does not allow electric charges (electricity) to flow through it.

Example glass, ebonite, rubber, plastic, paper, dry air, dry wood, cotton, mica, backelite, porcelain and dry leather are all insulators because they do not allow electric charges (electricity) to flow through them.  Rubber is an excellent insulator, and wood is also a good insulator.

CONDUCTORS, RESISTORS, AND INSULATORS  

On the basis of their electric resistance, all substances can be divided into three groups. Conductor,  Resistor, and Insulator.

RESISTORS 

Those substances that have comparatively high electrical resistance are called resistors. The alloy like nichrome, manganin, and constantan all has quite high resistance, so they are called resistors. The resistor reduces the current in a circuit.

OHMIC AND NON-OHMIC RESISTORS

Resistors that follow Ohm’s Law are called Ohmic resistors, and those that do not follow it are called non-Ohmic resistors.

SemiConductor

The resistivity of semiconductors like silicon and germanium is between that of a conductor and an insulator and decreases with increasing temperature.

SUPERCONDUCTORS

Conductors that offer zero resistance to the flow of current are called superconductors. Prominent examples of superconductors include aluminium, niobium, magnesium diboride, and cuprates such as yttrium barium, copper oxide, and iron pnictides.