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Cheat sheet · Class 10 · CBSE Science

Electricity cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 10 · Science

Cheat sheet

Chapter 11Electricity

V = IR keeps every circuit in check.

1. Current, Potential, Ohm's Law

I=QtI = \dfrac{Q}{t} (A)V=WQV = \dfrac{W}{Q} (V)V=IRV = IR (Ω)
  • 1 A = 1 C/s; charge of electron = 1.6×10−191.6 \times 10^{-19} C; 1 C ≈ 6×10186 \times 10^{18} electrons
  • Conventional current flows + to −, opposite to electrons
  • Ammeter in series (low R); voltmeter in parallel (high R)
  • Ohm's law: V ∝ I at constant temperature; V–I graph is a straight line

Resistance & resistivity

R=ρlAR = \rho \dfrac{l}{A}ρ in Ω m

R ∝ length, ∝ 1/area; depends on material and temperature. Alloys (nichrome) have high ρ – used in heaters. Conductors: ρ from 10−810^{-8} to 10−610^{-6} Ω m.

2. Resistors in Circuits

Series

Rs=R1+R2+R3R_s = R_1 + R_2 + R_3

Same current; voltage divides. One fails → all stop.

Parallel

1Rp=1R1+1R2+1R3\dfrac{1}{R_p} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + \dfrac{1}{R_3}

Same voltage; current divides. RpR_p < smallest R.

Homes use parallel wiring: each appliance gets full voltage and can be switched separately.

Circuit symbols to know

  • Cell
  • Battery
  • Resistor
  • Rheostat
  • Ammeter (A)
  • Voltmeter (V)

3. Heating Effect

Joule's law: H=I2RtH = I^2Rt

Used in heaters, irons, toasters, bulbs (tungsten, m.p. 3380 °C, bulbs filled with N₂/Ar) and fuses (low m.p. alloy, in series).

4. Electric Power & Energy

P=VI=I2R=V2RP = VI = I^2R = \dfrac{V^2}{R} (W)

1 kWh = 1 'unit' = 3.6×106\mathbf{3.6 \times 10^{6}} J. Energy = P × t.

Example: 100 W bulb for 10 h = 1 kWh = 1 unit.

5. Key Points to Remember

  • Ammeter in series, voltmeter in parallel.
  • Resistance doubles if length doubles; quarters if diameter doubles.
  • Parallel combination gives less resistance than any single resistor.
  • Fuse wire melts when current is too high.
  • Unit of ρ is Ω m; unit of power is watt.
  • 1 kWh = 3.6 MJ.

Remember: V = IR | R = ρl/A | H = I²Rt | P = VI

Electricity: questions and notes

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