Electricity Short Notes Class 10, Short And Concise!

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“Electricity Short Notes” has been prepared from your NCERT textbook, keeping in mind the most repeated questions.

Before turning to these notes, read the chapter from the NCERT book.

Table of Contents

Electric Current

  • Electric current: flow of electric charge through a conductor
  • In metallic wires → charges are electrons

Electric Circuit

  • Electric circuit: a continuous and closed path of electric current
  • Switch ON → conducting link between cell and bulb
  • Switch OFF / break in circuit → current stops → bulb does not glow

Direction of
Electric Current

  • Conventional direction of current: direction of positive charge flow
  • Electron flow: opposite to conventional current
  • Direction of electric current: Oppositeto the direction offlow of negative charge.

Expression of Electric Current

Electric current = rate of flow of charge


𝑰=𝑸𝒕% Thick border (4pt) \fcolorbox{grey}{white}{$\boldsymbol{\displaystyle I = \frac{Q}{t}}$}

Where:

  • (I) = current
  • (Q) = charge
  • (t) = time

Units of Charge and Current

SI unit of charge:

coulomb (C)

1 C≈6×1018electrons1~C \approx 6 \times 10^{18} \quad electrons

Charge of one electron:


1.6×10−19 C1.6 \times 10^{-19}~C

SI unit of current: ampere (A)


1 A=1 C1 s1~A = \frac{1~C}{1~s}

Smaller Units

  • 1 mA=10−3 A1~mA = 10^{-3}~A
  • 1 μA=10−6 A1~\mu A = 10^{-6}~A

Measurement of
Electric Current

  • Instrument: Ammeter
  • Connection: Series
  • Current flows from the positive terminal
    to the negative terminal of the cell (conventional)
Keywords and Meanings
KeywordMeaning
Electric currentFlow of electric charge
Electric circuitClosed path for current
SwitchMakes or breaks circuit
Conventional currentFlow of positive charges
Electron flowActual charge flow in metals
Coulomb (C)Unit of electric charge
Ampere (A)Unit of electric current
AmmeterMeasures current

Electric Potential and Potential Difference

Cause of the Flow
of Electric Charges

  • Charges do not flow by themselves in a conductor
  • Flow occurs only when a potential difference exists
  • Similar to water flow due to a pressure difference
  • Electrons move due to electric pressure (potential difference)
  • Gravity has no role

Source of Potential Difference

  • Produced by a battery / electric cell
  • Due to chemical action inside the cell
  • Potential difference exists even when no current flows
  • When connected to a circuit → charges move → electric current
  • Cell expends chemical energy to maintain current

Electric Potential
Difference (Definition)

work done to move a unit charge
from one point to another


𝐕=𝐖𝐐\fcolorbox{gret}{white}{$\mathbf{\displaystyle V = \frac{W}{Q}}$}

Where:

  • (V) = potential difference
  • (W) = work done
  • (Q) = charge

SI Unit of
Potential Difference

  • Unit: volt (V)
  • Named after Alessandro Volta
  • 1 volt: work of 1 joule to move 1 coulomb


𝟏 𝐕=𝟏 𝐉𝟏 𝐂\fcolorbox{grey}{white}{$\mathbf{\displaystyle 1~V = \frac{1~J}{1~C}}$}


1 V=1 J C−1\fcolorbox{grey}{white}{$\boldsymbol{\displaystyle 1~\mathrm{V} = 1~\mathrm{J}~\mathrm{C}^{-1}}$}

Measurement
of Potential Difference

  • Instrument: Voltmeter
  • Connection: Parallel
  • Connected across two points
  • where a potential difference is measured
Keywords and Meanings
KeywordMeaning
Potential differenceWork done per unit charge
Electric pressureCause of charge flow
Volt (V)Unit of potential difference
VoltmeterMeasures potential difference
Battery / cellSource of potential difference
Chemical energyEnergy spent to maintain current
Acids Bases And Salts Short Notes Class 10
Acids, Bases And Salts Short Notes Class 10

Circuit Diagram

Electric Circuit (Components)

  • An electric circuit comprises:
    • Cell/battery
    • Plug key
    • Electrical component(s)
    • Connecting wires

Ohm’s Law

Relationship Between Current and Potential Difference

  • For a given conductor:
    • Ratio (V/I) same in each case
    • V–I graph → straight line through origin
  • Hence V/I = constant

Statement of
Ohm’s Law

  • Given a metallic wire
  • Temperature constant
  • Potential difference is directly proportional to current

𝐕∝𝐈 \fcolorbox{grey}{white}{$\mathbf{V \propto I}$}

𝑽𝑰=constant=𝑹\fcolorbox{grey}{white}{$\boldsymbol{\displaystyle \frac{V}{I} = \text{constant} = R}$}

𝑽=𝑰𝑹\fcolorbox{grey}{white}{$\boldsymbol{\displaystyle V = IR}$}

Resistance

  • Resistance (R): property of a conductor
    to resist the flow of charges
  • Constant for a given wire at a given temperature
  • SI unit: ohm (Ω)

𝑹=𝑽𝑰\fcolorbox{grey}{white}{$\boldsymbol{\displaystyle R = \frac{V}{I}}$}

1 𝛀=1 V1 A\fcolorbox{grey}{white}{$\boldsymbol{\displaystyle 1~\Omega = \frac{1~\mathrm{V}}{1~\mathrm{A}}}$}

Current–Resistance Relation

𝑰=𝑽𝑹 \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I = \frac{V}{R}}$}

  • Current is inversely proportional to resistance
  • Resistance doubled → current halved

Variable Resistance

  • Used to increase or decrease the current
  • Voltage source unchanged
  • Device used: Rheostat

Motion of Electrons
and Resistance

  • Electric current → motion of electrons
  • Electrons not completely free
  • Atoms restrain electron motion
  • Resistance retards motion of electrons
Types of Materials (Same Size)
Material TypeResistance
Good conductorLow resistance
ResistorAppreciable resistance
Poor conductorHigher resistance
InsulatorVery high resistance

Factors Affecting Resistance of a Conductor

Resistance depends on:

  1. Length
  2. Area of cross-section
  3. Nature of material

Length

  • Length doubled → current halves
    𝑹∝𝒍\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle R \propto l}$}

Area of Cross-Section

  • Thicker wire → higher current
    𝑹∝1𝑨\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle R \propto \frac{1}{A}}$}

Combined Relation

𝑹∝𝒍𝑨 \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle R \propto \frac{l}{A}}$}

𝑹=𝝆𝒍𝑨\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle R = \rho \frac{l}{A}}$}

Resistivity

  • Resistivity 𝝆\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle \rho}$} (rho): a characteristic property of a material
  • SI unit: Ω m
  • Varies with temperature
Resistivity of Materials
Material TypeResistivity Range
Metals/alloys10−8 to 10−6 𝛀⋅m\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 10^{-8} \ \text{to} \ 10^{-6} \ \Omega \cdot \mathrm{m}}$}
Insulators1012 to 1017 𝛀⋅m\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 10^{12} \ \text{to} \ 10^{17} \ \Omega \cdot \mathrm{m}}$}

Alloys and Uses

  • Alloy resistivity is higher than that of constituent metals
  • Do not oxidise easily at high temperatures
  • Used in electric irons, toasters
  • Tungsten → bulb filament
  • Copper & aluminium → transmission lines
Keywords and Meanings
KeywordMeaning
Ohm’s lawRelation between V and I
ResistanceOpposition to charge flow
RheostatVariable resistance device
ResistivityMaterial property
Good conductorLow resistance
InsulatorVery high resistance

Resistance of a System of Resistors

Combination of Resistors

  • Resistors are used in various combinations
  • Ohm’s law applied to combined resistors
  • Two methods:
    • Series
    • Parallel

Resistors in Series

Series Connection

  • Resistors joined end-to-end
  • The same current flows through each resistor
  • Ammeter reading same at all positions

Current in Series

  • Let the current be I
  • Current through each resistor = I

Potential Difference in Series

  • Total potential difference:
    𝐕=𝐕𝟏+𝐕𝟐+𝐕𝟑\fcolorbox{gray}{white}{$\mathbf{V = V_1 + V_2 + V_3}$}

Equivalent Resistance (Series)

Using Ohm’s law:

𝑽=𝑰𝑹\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle V = IR}$}

For individual resistors:

𝑽1=𝑰𝑹1,𝑽2=𝑰𝑹2,𝑽3=𝑰𝑹3\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle V_1 = IR_1,\quad V_2 = IR_2,\quad V_3 = IR_3}$}

𝑰𝑹=𝑰𝑹1+𝑰𝑹2+𝑰𝑹3\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle IR = IR_1 + IR_2 + IR_3}$}

𝑹𝒔=𝑹1+𝑹2+𝑹3\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle R_s = R_1 + R_2 + R_3}$}

  • Series resistance = sum of individual resistances
  • Greater than any individual resistance

Resistors in Parallel

Parallel Connection

  • Resistors connected across same two points
  • Potential difference same across each resistor

Current in Parallel

  • Total current:
    𝑰=𝑰1+𝑰2+𝑰3\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I = I_1 + I_2 + I_3}$}

Equivalent Resistance (Parallel)

Using Ohm’s law:

𝑰=𝑽𝑹𝒑\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I = \frac{V}{R_p}}$}

For individual resistors:

𝑰1=𝑽𝑹1,𝑰2=𝑽𝑹2,𝑰3=𝑽𝑹3\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I_1 = \frac{V}{R_1},\quad I_2 = \frac{V}{R_2},\quad I_3 = \frac{V}{R_3}}$}

1𝑹𝒑=1𝑹1+1𝑹2+1𝑹3 \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle \frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}}$}

  • Reciprocal of equivalent resistance = sum of reciprocals
  • Parallel resistance decreases
Comparison: Series vs Parallel
AspectSeries CircuitParallel Circuit
CurrentSame everywhereDivides
Potential differenceDividesSame
Equivalent resistanceIncreasesDecreases
Failure of one deviceWhole circuit breaksOthers work
Use in practiceImpracticable for devicesSuitable for gadgets
Practical Observations
  • Series:
    • Same current everywhere
    • Not suitable for devices needing different currents
    • One failure → whole circuit stops
  • Parallel:
    • Current divides among devices
    • Suitable for gadgets with different resistances
    • Total resistance reduced
Keywords and Meanings
KeywordMeaning
Series combinationEnd-to-end connection
Parallel combinationSame two points connection
Equivalent resistanceSingle resistance replacing combination
Branch currentCurrent in each parallel path
Total currentSum of branch currents

Heating Effect of Electric Current

Source of Energy

  • Cell/battery → source of electrical energy
  • Chemical reaction → produces potential difference
  • Potential difference → electrons move → current flows
  • To maintain the current → source expends energy

Energy Conversion

  • Source energy used for:
    • Useful work (e.g. rotating fan blades)
    • Heat production
  • In a purely resistive circuit:
    • Energy is completely converted into heat
  • This phenomenon is called the heating effect of electric current

Heating Effect

  • Heat is produced when current
    flows through a resistor
  • Used in:
    • Electric heater
    • Electric iron

Heat Produced in a Resistor

Let:

  • Current = (I)
  • Resistance = (R)
  • Potential difference = (V)
  • Time = (t)
  • Charge = (Q)

1. Work Done

𝑾=𝑽𝑸\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle W = VQ}$}

2. Power Supplied

𝑷=𝑽𝑸𝒕=𝑽𝑰\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle P = \frac{VQ}{t} = VI}$}

3. Heat Produced

𝑯=𝑽𝑰𝒕\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H = VIt}$}

Joule’s Law of Heating

Using Ohm’s law:

𝑯=𝑰2𝑹𝒕 \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H = I^2 R t}$}

Implications

Heat produced:

  1. 𝑯∝𝑰2(for given 𝑹)\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H \propto I^2 \quad (\text{for given } R)}$}
  2. 𝑯∝𝑹(for given 𝑰) \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H \propto R \quad (\text{for given } I)}$}
  3. 𝑯∝𝒕\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H \propto t}$}

Practical Use
of Formula

  • Appliance connected to a known voltage
  • First calculate:
    𝑰=𝑽𝑹\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I = \frac{V}{R}}$}
  • Then use:
    𝑯=𝑰2𝑹𝒕\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle H = I^2 R t}$}

Applications of the Heating Effect

Electrical Appliances

  • Electric iron
  • Electric toaster
  • Electric oven
  • Electric kettle
  • Electric heater

Electric Bulb

  • Heating is used to produce light
  • Filament:
    • Retains heat
    • Gets very hot → emits light
    • Must not melt
  • Material used: Tungsten
    • High melting point: 3380°C
  • Filament:
    • Thermally isolated
    • Bulb filled with nitrogen and argon
  • Most energy → heat
  • Small part → light

Fuse (Application of Heating Effect)

  • Fuse: safety device
  • Connected in series
  • Protects the circuit from excess current
  • Made of metal/alloy with low melting point
  • Excess current → temperature rises → fuse melts → circuit breaks

Fuse Details

FeatureDescription
MaterialAluminium, copper, iron, lead
Fuse ratings1 A, 2 A, 3 A, 5 A, 10 A
EncasingPorcelain cartridge

Fuse Selection Example

  • Electric iron power = 1 kW
  • Voltage = 220 V

𝑰=1000220=4.54 A\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle I = \frac{1000}{220} = 4.54~\mathrm{A}}$}

  • Required fuse: 5 A
Keywords and Meanings
KeywordMeaning
Heating effectHeat due to electric current
Joule’s lawHeat–current–resistance relation
Resistive circuitCircuit with only resistors
FilamentThin wire emitting light
FuseSafety device that melts

Electric Power

Meaning of Power

  • Power: rate of doing work
  • Also rate of consumption of energy
  • In an electric circuit → rate at which
    electric energy is dissipated

Electric Power

  • Electric power: rate of electrical energy consumption in a circuit

Formulae

𝑷=𝑽𝑰 \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle P = VI}$}

Using Ohm’s law: V = IR

𝑷=𝑰2𝑹\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle P = I^2 R}$}

𝑷=𝑽2𝑹\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle P = \frac{V^2}{R}}$}

SI Unit of Electric Power

  • Unit: watt (W)
  • Definition:
    • Power when 1 A current flows at 1 V

1 W=1 V×1 A\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{W} = 1~\mathrm{V} \times 1~\mathrm{A}}$}

1 W=1 VA\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{W} = 1~\mathrm{VA}}$}

Larger Unit of Power

  • Kilowatt (kW):
    1 kW=1000 W\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{kW} = 1000~\mathrm{W}}$}

Electric Energy

  • Electric energy = power × time
  • Unit: watt hour (Wh)

Definition

  • 1 Wh: energy used by 1 W in 1 hour

Commercial Unit of Electric Energy

  • Kilowatt hour (kWh)
  • Commonly called unit

1 kWh=1000 W×3600 s \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{kWh} = 1000~\mathrm{W} \times 3600~\mathrm{s}}$}

1 kWh=3.6×106 Ws \fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{kWh} = 3.6 \times 10^6~\mathrm{Ws}}$}

1 kWh=3.6×106 J\fcolorbox{gray}{white}{$\boldsymbol{\displaystyle 1~\mathrm{kWh} = 3.6 \times 10^6~\mathrm{J}}$}

Keywords and Meanings
KeywordMeaning
Electric powerRate of energy consumption
Watt (W)SI unit of power
Kilowatt (kW)1000 watts
Watt hour (Wh)Unit of electric energy
Kilowatt hour (kWh)Commercial unit of energy
UnitkWh

Conclusion: Electricity Short Notes

Read the notes repeatedly for quick recall during examinations. Your NCERT chapter on electricity is essential to scoring well. Hence, the best way to get maximum benefit from these notes is to read the topic from the NCERT and then from these notes.

If you have any doubts, questions or need some other help, please contact us.

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