Class 10 Science Chapter 11 Electricity Short Notes

Contents hide
1Formulas at a Glance
2Named Scientists
3Circuit Symbols
Ammeter
Voltmeter
4Series vs Parallel
Series
Parallel
5Resistivity Table (Ω m)
6Practical Facts to Remember

A quick revision summary for right before the exam: every definition, formula and key fact, all in one place. The full notes are available separately for detailed reading.

Definitions to revise
Electric circuitA continuous, closed path along which current flows
Electric currentRate of flow of charge, I=Q/tI=Q/t, unit ampere (A)
Potential differenceWork done per unit charge moved between two points, V=W/QV=W/Q, unit volt (V)
Ohm’s lawV∝IV\propto I at constant temperature, so V=IRV=IR
ResistanceOpposition to current flow, R=V/IR=V/I, unit ohm (Ω\Omega)
Resistivity (ρ\rho)A material’s own resistance property, R=ρl/AR=\rho l/A, unit Ω\Omega m
RheostatDevice to change resistance without changing the source voltage
Joule’s law of heatingH=I2RtH=I^2Rt
FuseSafety wire in series that melts and breaks the circuit above a rated current
Electric powerRate of using electrical energy, P=VI=I2R=V2/RP=VI=I^2R=V^2/R, unit watt
Kilowatt hourCommercial energy unit (“unit” on the bill), 1 kWh=3.6×106 J1\ \mathrm{kWh}=3.6\times10^6\ \mathrm{J}

1Formulas at a Glance

Quantity Formula SI Unit
Current I=Q/tI=Q/t ampere (A)
Potential difference V=W/QV=W/Q volt (V)
Ohm’s law V=IRV=IR a relationship
Resistance R=V/I=ρl/AR=V/I=\rho l/A ohm (Ω\Omega)
Series combination Rs=R1+R2+R3R_s=R_1+R_2+R_3 ohm (Ω\Omega)
Parallel combination 1/Rp=1/R1+1/R2+1/R31/R_p=1/R_1+1/R_2+1/R_3 ohm (Ω\Omega)
Heat produced (Joule’s law) H=VIt=I2RtH=VIt=I^2Rt joule (J)
Electric power P=VI=I2R=V2/RP=VI=I^2R=V^2/R watt (W)
Commercial energy unit 1 kWh=3.6×106 J1\ \mathrm{kWh}=3.6\times10^6\ \mathrm{J} kilowatt hour (kWh)

2Named Scientists

Unit Named after Field / dates
Ampere (current) Andre-Marie Ampere French scientist, 1775-1836
Volt (potential difference) Alessandro Volta Italian physicist, 1745-1827
Ohm’s law Georg Simon Ohm German physicist, 1787-1854; found 1827

3Circuit Symbols

A

Ammeter

Measures current. Connected in series.

V

Voltmeter

Measures potential difference. Connected in parallel.

4Series vs Parallel

Series

  • Same current everywhere: II
  • Voltages add: V=V1+V2+V3V=V_1+V_2+V_3
  • Resistances add: Rs=R1+R2+R3R_s=R_1+R_2+R_3
  • One failure breaks the whole circuit

Parallel

  • Same voltage across each branch: VV
  • Currents add: I=I1+I2+I3I=I_1+I_2+I_3
  • Reciprocal resistances add: 1/Rp=∑1/Ri1/R_p=\sum 1/R_i
  • One failure does not affect the rest

5Resistivity Table (Ω m)

Material Resistivity
Best conductors Silver 1.60×10−81.60\times10^{-8}
Copper 1.62×10−81.62\times10^{-8}
Aluminium 2.63×10−82.63\times10^{-8}
Alloys (heating devices) Manganin 44×10−644\times10^{-6}
Constantan 49×10−649\times10^{-6}
Nichrome 100×10−6100\times10^{-6}
Insulators Glass, rubber, ebonite 101010^{10} to 101710^{17}

6Practical Facts to Remember

3380°Cmelting point of tungsten (bulb filament)
N₂ + Argases used to fill bulbs
1,2,3,5,10 Astandard domestic fuse ratings
Quick Revision: read this the night before the exam
  • Current is opposite in direction to electron flow
  • Ammeter: series. Voltmeter: parallel. Never swap these.
  • R∝lR\propto l, R∝1/AR\propto 1/A: longer wire, more resistance; thicker wire, less resistance
  • Alloys resist oxidising at high temperature, which is why heating coils use nichrome, not pure metal
  • Homes are wired in parallel, not series
  • Fuse is always in series, and melts to break the circuit on overcurrent
  • Electrons are never consumed; we pay for the energy used to move them
More for this chapter
NotesImportant QuestionsMCQ / ObjectiveNCERT Solutions