MP Board Class 10 Science Chapter 11: Electricity – Notes, Formulas & Practice Questions

Electricity is one of the most scoring chapters in MP Board Class 10 Science. This chapter covers electric current, circuits, Ohm’s law, resistance, heating effects, and power. Understanding numericals is key — at least 2-3 numerical questions come from this chapter every year.

📚 Key Concepts

• Electric Current (I): Flow of electric charge.
  Formula: I = Q / t (Amperes) where Q = charge in coulombs, t = time in seconds
• Electric Potential Difference (V): Work done per unit charge.
  Formula: V = W / Q (Volts) where W = work done in joules
• Ohm’s Law: V = I × R — Current through a conductor is directly proportional to the potential difference across it, provided temperature remains constant.
• Resistance (R): Opposition to flow of current.
  Formula: R = ρ × (L / A) where ρ = resistivity, L = length, A = cross-sectional area
• Factors affecting Resistance: Length (↑L → ↑R), Area (↑A → ↓R), Material (ρ), Temperature (↑T → ↑R for metals)
• Resistors in Series: R_eq = R₁ + R₂ + R₃ + … — Current same, voltage divides
• Resistors in Parallel: 1/R_eq = 1/R₁ + 1/R₂ + 1/R₃ + … — Voltage same, current divides
• Heating Effect of Electric Current (Joule’s Law): H = I² × R × t (Joules) — Heat produced when current flows through a resistor
• Electric Power (P): P = V × I = I² × R = V² / R (Watts)
• Electrical Energy: E = P × t — Measured in kilowatt-hours (kWh). 1 kWh = 3.6 × 10⁶ J

📐 Important Formulas (Must Memorize)

🔌 Circuit Diagram Symbols

• Cell/Battery: Long and short parallel lines (Long = positive, Short = negative)
• Resistor: Zigzag line ( ) or rectangle box
• Ammeter: Circle with ‘A’ — connected in series
• Voltmeter: Circle with ‘V’ — connected in parallel
• Key/Switch: Open gap (off) / joined line (on)
• Rheostat: Variable resistor symbol

⚡ MP Board Important Questions (PYQs)

1 Mark Questions

1. Define 1 ampere of current.
2. State Ohm’s Law.
3. What is the SI unit of resistivity?
4. How are ammeter and voltmeter connected in a circuit?
5. Write the formula for heat produced in a resistor.

3 Mark Questions

1. A wire of resistance 5 Ω is stretched to double its length. What is the new resistance?
   Solution: R ∝ L² (since volume constant). New R = 5 × 4 = 20 Ω
2. Two resistors of 6 Ω and 3 Ω are connected in parallel. Find the equivalent resistance.
   Solution: 1/R = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 → R = 2 Ω
3. An electric iron consumes 1.5 kW power at 250 V. Find the current drawn.
   Solution: I = P/V = 1500/250 = 6 A

5 Mark Numerical Questions

1. A 4 Ω resistor is connected in series with a parallel combination of two resistors of 6 Ω and 3 Ω. The circuit is connected to a 12 V battery. Find:
   (a) Total resistance
   (b) Total current
   (c) Current through each resistor
   Solution: Parallel: 1/Rp = 1/6 + 1/3 = 1/2 → Rp = 2 Ω. Series: Total R = 4 + 2 = 6 Ω. Total I = 12/6 = 2 A. V across parallel = 2×2 = 4 V. I through 6 Ω = 4/6 = 0.67 A, I through 3 Ω = 4/3 = 1.33 A
2. A house has 5 bulbs of 60 W each used for 6 hours daily. Calculate:
   (a) Energy consumed per day in kWh
   (b) Cost of electricity for 30 days at ₹8 per unit
   Solution: Total power = 5 × 60 = 300 W = 0.3 kW. Energy/day = 0.3 × 6 = 1.8 kWh. Energy/month = 1.8 × 30 = 54 kWh. Cost = 54 × 8 = ₹432

📝 Practice Questions (Try Yourself)

1. Calculate the resistance of a copper wire of length 2 m and area of cross-section 1 mm². (Resistivity of copper = 1.62 × 10⁻⁸ Ωm)
2. Three resistors of 2 Ω, 4 Ω, and 6 Ω are connected in series. Find the equivalent resistance.
3. An electric heater draws 5 A current from a 220 V supply. What is its power? Calculate the heat produced in 30 minutes.
4. Why are alloys used in heating devices instead of pure metals?
5. Explain why bulbs have thin filaments but thick connecting wires.

💡 Key Points for MP Board Exam

• Current flows from positive to negative terminal (conventional direction)
• Electrons actually flow from negative to positive
• 1 kWh = 3.6 × 10⁶ J — called 1 “unit” of electricity
• Good conductors: Silver (lowest resistivity), Copper, Aluminum
• Insulators: Rubber, Plastic, Glass, Wood — very high resistivity
• Alloys like Nichrome (Ni + Cr) have high resistivity — used in heating elements
• Bulk of numericals come from: Ohm’s Law, Series-Parallel, Joule’s Heating, Power

🎯 MP Board Exam Tips

• Always write Given → Formula → Substitution → Answer with unit
• Draw circuit diagrams neatly with a ruler — 1 mark reserved for neatness
• In numericals, convert units properly (mA → A, kW → W, mm² → m², min → sec)
• This chapter typically carries 10-14 marks in MP Board exams

📥 Download PDF version — Bookmark this page for quick revision before your MP Board 2027 exams!

✅ Study this chapter along with NCERT textbook exercises and MP Board previous year papers for best results.