Class 10 Ch 11 Electricity

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Electricity – 5-Page Study Notes
Ch-11: Electricity ⚡
1. Electric Current (विद्युत धारा)
  • Flow of electric charge in a conductor.
  • आवेश के प्रवाह की दर को विद्युत धारा कहते हैं।
  • Formula: $I = \frac{Q}{t}$ where $Q = ne$ ($n$=no. of $e^-$, $e$=charge on 1 $e^-$).
  • SI Unit: Ampere (A). $1A = 1 C/s$.
  • Measured by: Ammeter (always connected in Series).
  • Direction: Conventional current flows from Positive to Negative terminal (opposite to electron flow).
2. Electric Potential & Difference
  • Potential Difference (V): Work done to move a unit charge from one point to another.
  • Formula: $V = \frac{W}{Q}$
  • SI Unit: Volt (V). $1V = 1 J/C$.
  • Measured by: Voltmeter (always connected in Parallel).
V Voltmeter A Ammeter
3. Circuit Symbols
🔋 Cell: ──┤├──
⚡ Battery: ──┤╢├──
🔘 Key (Open): ──( )──
🔘 Key (Closed): ──(•)──
💡 Bulb: ──󱐋──
📐 Resistor: ──/\/\/\──
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4. Ohm’s Law (ओम का नियम)
  • At constant temperature, current ($I$) is directly proportional to potential difference ($V$).
  • नियत ताप पर, विभवांतर धारा के समानुपाती होता है।
  • $V \propto I \implies V = IR$
  • Where $R$ is Resistance (Unit: Ohm $\Omega$).

V-I Graph (Straight Line)

I V
5. Factors Affecting Resistance
  • 1. Length ($L$): $R \propto L$.
  • 2. Area ($A$): $R \propto \frac{1}{A}$ (Thick wire $\to$ Less $R$).
  • 3. Material: Resistivity ($\rho$).
  • Formula: $R = \rho \frac{L}{A}$
  • SI Unit of $\rho$: $\Omega \cdot m$.
IMP: Resistivity does NOT change with length or area. It only changes with Material and Temperature.
Metals/Alloys $\to$ Low $\rho$ | Insulators $\to$ High $\rho$.
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6. Resistors in Series (श्रेणीक्रम)
  • Connected end-to-end.
  • Current ($I$): Same in all resistors.
  • Voltage ($V$): Sum of individual voltages ($V = V_1 + V_2 + V_3$).
  • Equivalent Resistance: $R_s = R_1 + R_2 + R_3$
  • Result: Total resistance increases.

Series Connection

R1R2
7. Resistors in Parallel (पार्श्वक्रम)
  • Connected between same two points.
  • Voltage ($V$): Same across all resistors.
  • Current ($I$): Divided ($I = I_1 + I_2 + I_3$).
  • Equivalent Resistance: $\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$
  • Result: Total resistance decreases.
Why Parallel in Homes?
1. If one appliance fuse, others keep working.
2. Each appliance gets same voltage (220V).
3. Overall resistance is low, so current flow is efficient.
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8. Heating Effect of Current (तापीय प्रभाव)
  • When current passes through a high-resistance wire (like Nichrome), it becomes hot and produces heat.
  • Joule’s Law of Heating: Heat ($H$) produced is:
    (i) $H \propto I^2$ (Square of current)
    (ii) $H \propto R$ (Resistance)
    (iii) $H \propto t$ (Time)
  • Formula: $H = I^2Rt$ (Unit: Joule $J$).
  • Also, $H = VIt$.
9. Practical Applications
  • Electric Bulb: Filament is made of Tungsten (Very high M.P. $3380^\circ C$). Filled with inactive gases like Nitrogen/Argon.
  • Electric Fuse: Safety device connected in Series. Made of alloy (Pb-Sn) with low melting point. It melts when current exceeds limit, breaking the circuit.
  • Electric Iron/Heater: Use Nichrome (Alloy) as it has high resistivity and doesn’t oxidise (burn) easily at high temp.
Fuse Wire
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10. Electric Power (विद्युत शक्ति)
  • Rate at which electric energy is consumed.
  • Formula: $P = VI = I^2R = \frac{V^2}{R}$
  • SI Unit: Watt (W). $1W = 1 J/s$.
  • $1 kW = 1000 W$.
11. Commercial Unit of Energy
  • Energy ($E$) = Power $\times$ Time.
  • Commercial Unit: kilowatt-hour (kWh), also called ‘Unit’.
  • Conversion: $1 kWh = 3.6 \times 10^6 J$.
  • व्यावसायिक इकाई किलोवाट-घंटा (kWh) है।
12. Chapter Summary

• $Q = It$ | $V = W/Q$ | $V = IR$

• $R = \rho L/A$

• Series: $R = \sum R_i$ | Parallel: $1/R = \sum 1/R_i$

• $H = I^2Rt$ | $P = VI$

• Tungsten for Bulb | Fuse for Safety | Parallel for Home.

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Danger ⚡
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