MP Board Class 10 Science Chapter 11: Electricity

MP Board Class 10 Science Chapter 11: Electricity (विद्युत) — Electricity is one of the most important chapters in the MP Board Class 10 Science syllabus, carrying 8–10 marks in the board exam. This chapter covers electric current, potential difference, Ohm’s law, resistance, combination of resistors, heating effect of electric current, and electric power. Understanding electricity is essential not just for exams but for everyday life — from household circuits to power consumption calculations. In this detailed guide, we provide complete notes, formulas, circuit diagrams, solved numericals, and previous year questions to help you score full marks.

⚡ 1. Electric Current and Circuit

Electric current is defined as the rate of flow of electric charge through a conductor. In simpler terms, it is the flow of electrons through a closed circuit.

Term Definition SI Unit Symbol
Electric Current Rate of flow of charge Ampere (A) I
Electric Charge Fundamental property of matter Coulomb (C) Q
Time Duration of current flow Second (s) t
🎯 Exam Tip: I = Q/t is the fundamental formula. If 10 C of charge flows through a conductor in 2 seconds, the current I = 10/2 = 5 A. Always remember — current is measured by an ammeter connected in series in the circuit.

What is an Electric Circuit?

A closed and continuous path through which electric current flows is called an electric circuit. It consists of:

  • Cell or Battery: Source of electrical energy
  • Connecting Wires: Provide path for current flow
  • Switch: Controls the flow of current (open = off, closed = on)
  • Bulb or Load: Converts electrical energy into light/heat
  • Ammeter & Voltmeter: Measure current and potential difference

📘 Key Fact: Conventional current flows from positive terminal to negative terminal, while electron flow (actual flow) is from negative to positive. In circuit diagrams, current direction is shown as conventional current (positive to negative).

🔋 2. Electric Potential and Potential Difference

Electric Potential (V): The amount of work done in bringing a unit positive charge from infinity to a point in an electric field is called electric potential at that point.

Potential Difference (V): The difference in electric potential between two points in a circuit. It is defined as the work done to move a unit charge from one point to another.

Quantity Formula SI Unit Measuring Device
Potential Difference V = W / Q Volt (V) Voltmeter (parallel)
Work Done W = V × Q Joule (J) —
🎯 Exam Tip: A voltmeter is always connected in PARALLEL across the component whose potential difference is to be measured. Never connect it in series — it will give incorrect readings and may damage the meter.

📐 3. Ohm’s Law and Resistance

Ohm’s Law states that at constant temperature, the potential difference (V) across the ends of a conductor is directly proportional to the current (I) flowing through it.

Ohm’s Law Formula: V = I × R   |   I = V / R   |   R = V / I

Where V = Potential difference (volt), I = Current (ampere), R = Resistance (ohm).

What is Resistance?

Resistance is the property of a conductor that opposes the flow of electric current through it. It depends on the material, length, cross-sectional area, and temperature of the conductor. The SI unit of resistance is ohm (Ω).

🎯 Exam Tip: If the V-I graph is a straight line passing through the origin, the conductor obeys Ohm’s law. Such conductors are called ohmic conductors (e.g., copper wire, nichrome wire). Non-ohmic conductors (e.g., diode, LED) have a curved V-I graph.

📏 4. Factors Affecting Resistance

The resistance of a conductor depends on four factors:

Factor Relationship Explanation
Length (l) R ∝ l Longer wire → more resistance
Area of Cross-Section (A) R ∝ 1/A Thicker wire → less resistance
Material (ρ) R = ρ × l / A Different materials have different resistivity
Temperature R ∝ Temperature More heat → more resistance (for metals)

📘 Key Fact: Resistivity (ρ) is a material-specific property. Silver has the lowest resistivity (1.6 × 10⁻⁸ Ωm), followed by copper (1.7 × 10⁻⁸ Ωm). This is why copper wires are commonly used in household wiring. Alloys like nichrome have much higher resistivity and are used in heating elements.

🔗 5. Combination of Resistors

Series Combination

In a series combination, resistors are connected end-to-end. The same current flows through each resistor.

Property Series Parallel
Effective Resistance Rs = R₁ + R₂ + R₃ 1/Rp = 1/R₁ + 1/R₂ + 1/R₃
Current Same through all resistors Divided among resistors
Voltage Divided (V = V₁ + V₂ + V₃) Same across all resistors
Effect if one fails Whole circuit breaks Other paths still work

Parallel Combination

In a parallel combination, resistors are connected such that both ends of each resistor are connected to the same two points. The voltage across each resistor is the same, and the current divides.

Numerical Example: If three resistors of 2Ω, 3Ω, and 6Ω are connected in parallel, find the effective resistance.
Solution: 1/Rp = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1
Therefore: Rp = 1 Ω
🎯 Exam Tip: In parallel combination, the effective resistance is always LESS than the smallest individual resistance. Hence, Rp = 1Ω is less than 2Ω (the smallest). This is a common trick question in MP Board exams!

🔥 6. Heating Effect of Electric Current

When electric current passes through a conductor, the conductor gets heated due to collisions of electrons with the atoms of the conductor. This is known as the heating effect of electric current.

Joule’s Law of Heating: H = I² × R × t
Where: H = Heat produced (Joules), I = Current (A), R = Resistance (Ω), t = Time (s)

Applications of Heating Effect

  • Electric Heater, Iron, Toaster: Nichrome wire (high resistivity, high melting point) is used as heating element
  • Electric Bulb: Tungsten filament — 90% heat, 10% light (inefficient but produces light as a byproduct of heat)
  • Electric Fuse: Safety device that melts when current exceeds safe limit — wire made of tin-lead alloy with low melting point
🎯 Exam Tip: Fuse wire is always connected in SERIES with the live wire. Rated at a specific current (e.g., 5A, 15A). When current exceeds the rating, the fuse melts and breaks the circuit — preventing damage to appliances.

💡 7. Electric Power

Electric power is defined as the rate at which electrical energy is consumed or produced. It is measured in watts (W).

Power Formula: P = V × I   |   P = I² × R   |   P = V² / R
Electrical Energy: E = P × t (in watt-hours or kilowatt-hours)
Commercial Unit: 1 kWh = 3.6 × 10⁶ J
Appliance Power Rating Energy Used (1 hour)
LED Bulb 10 W 0.01 kWh
Ceiling Fan 75 W 0.075 kWh
Refrigerator 150 W 0.15 kWh
Air Conditioner 1500 W 1.5 kWh
🎯 Exam Tip: A common numerical question: “Calculate the cost of running a 100W bulb for 10 hours if electricity costs ₹6/kWh.”
Energy = 100W × 10h = 1000 Wh = 1 kWh. Cost = 1 × 6 = ₹6. Always convert watts to kilowatts first.

📝 8. Important Formulae Summary

S.No. Formula Description
1 I = Q / t Electric current = Charge / Time
2 V = W / Q Potential difference = Work / Charge
3 V = I × R Ohm’s Law
4 R = ρ × l / A Resistance formula with resistivity
5 Rs = R₁ + R₂ + R₃ Series combination
6 1/Rp = 1/R₁ + 1/R₂ + 1/R₃ Parallel combination
7 H = I² × R × t Joule’s heating law
8 P = V × I Electric power
9 E = P × t Electrical energy

📋 Previous Year Questions (2017–2026)

Year Question Marks
2025 State Ohm’s law. A wire of resistance 5Ω is stretched to double its length. What will be the new resistance? 3
2024 Three resistors of 2Ω, 3Ω, and 5Ω are connected in series. Find the effective resistance and current flowing if connected to a 10V battery. 4
2024 Explain the heating effect of electric current with two applications. 3
2023 Define electric power. A 100W bulb is used for 5 hours daily. Calculate the energy consumed in 30 days in kWh. 4
2023 Differentiate between series and parallel combination of resistors. 3
2022 A wire of resistance 10Ω is bent to form a closed circle. What is the effective resistance between two points at the ends of any diameter? 5
2022 What is the function of an electric fuse? Explain with a diagram. 3
2021 Calculate the resistance of a 2m long copper wire of cross-sectional area 2 × 10⁻⁶ m². (Resistivity of copper = 1.7 × 10⁻⁸ Ωm) 4
2021 Define resistivity. On what factors does the resistance of a conductor depend? 3
2020 An electric iron of 750W is used for 2 hours daily. Calculate the electricity bill for 30 days at ₹5 per kWh. 5
2019 Explain with a labelled diagram the components of an electric circuit. 3
2018 Two resistors of 6Ω each are connected (a) in series (b) in parallel. Calculate the effective resistance in each case. 4

❓ Frequently Asked Questions

Q1. What is the difference between electric current and electric charge?

Answer: Electric charge (Q) is a fundamental property of matter that causes electrostatic forces — measured in coulombs. Electric current (I) is the rate of flow of charge through a conductor — measured in amperes. I = Q/t. Charge exists even when stationary; current only flows when charges are in motion.

Q2. Why is tungsten used as filament in electric bulbs?

Answer: Tungsten has a very high melting point (3422°C), high resistivity, and does not oxidise readily. When current passes through the thin tungsten filament, it becomes white hot and emits light. The bulb is filled with inert gas (argon + nitrogen) to prevent the filament from burning.

Q3. What is the importance of Ohm’s law in daily life?

Answer: Ohm’s law helps in designing electrical circuits, selecting the correct fuse rating, determining wire thickness for household wiring, and calculating energy consumption. It is the foundation of all electrical engineering and circuit analysis.

Q4. Why is parallel combination preferred in household circuits?

Answer: In parallel combination: (i) each appliance gets the same voltage (220V), (ii) appliances can be switched on/off independently without affecting others, (iii) if one appliance fails, others continue working, (iv) adding more appliances doesn’t reduce the voltage across existing ones.

Q5. What is one ampere?

Answer: One ampere is the current flowing through a conductor when one coulomb of charge passes through a cross-section of the conductor in one second. 1 A = 1 C/s.

Q6. What is an electric fuse and how does it work?

Answer: An electric fuse is a safety device that protects electrical circuits from damage due to excessive current (overloading or short circuit). It consists of a thin wire made of tin-lead alloy with a low melting point. When current exceeds the rated value, the fuse wire heats up beyond its melting point and breaks the circuit, stopping current flow.

Q7. What is the commercial unit of electrical energy?

Answer: The commercial unit of electrical energy is kilowatt-hour (kWh). 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J. Electricity bills are calculated in kWh (commonly called “units”).

Q8. Why are copper and aluminium used in household wiring?

Answer: Copper and aluminium have very low resistivity (1.7 × 10⁻⁸ Ωm and 2.8 × 10⁻⁸ Ωm respectively), are ductile (can be drawn into thin wires), have good tensile strength, and are relatively inexpensive. They allow efficient current flow with minimal energy loss due to heating.

Q9. What is the difference between an ammeter and a voltmeter?

Answer: An ammeter measures electric current (in amperes) flowing through a circuit — it is connected in SERIES and has very low resistance (ideally zero). A voltmeter measures potential difference (in volts) across two points — it is connected in PARALLEL and has very high resistance (ideally infinite).

Q10. What is the power rating of common household appliances?

Answer: Common power ratings: LED bulb (5–15W), CFL bulb (15–25W), ceiling fan (60–75W), tube light (40W), refrigerator (100–250W), washing machine (500–2000W), microwave oven (800–1500W), air conditioner (1500–2500W), electric iron (750–1500W), water heater/immersion rod (1000–3000W).

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