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 Class 10 Science, carrying 15–18 marks in the MP Board board exam. This chapter covers the fundamentals of electric current, potential difference, Ohm’s law, resistance, series and parallel circuits, heating effect of electric current, and electric power. Understanding these concepts is essential for scoring high marks in both theory and numerical sections. This detailed notes and previous year questions guide will help you master the chapter and ace your 2027 board exam.

📑 Table of Contents

1. Electric Current and Circuit
2. Electric Potential and Potential Difference
3. Ohm’s Law and Resistance
4. Series and Parallel Combination of Resistors
5. Heating Effect of Electric Current
6. Electric Power and Commercial Unit
7. Important Numericals
Previous Year Questions (2017–2026)
Frequently Asked Questions

⚡ 1. Electric Current and Circuit

Electric Current is defined as the rate of flow of electric charge through a conductor. It is measured in amperes (A). If Q charge flows through a conductor in time t, then electric current I = Q/t.

Formula: I = Q/t where I = current (A), Q = charge (C), t = time (s)
1 ampere = 1 coulomb / 1 second

Electric Circuit

A closed path through which electric current flows is called an electric circuit. It consists of a cell/battery, connecting wires, a switch, and a load (bulb, resistor, etc.).

Types of Circuits

Property	Open Circuit	Closed Circuit
Switch position	OFF	ON
Current flow	No current flows	Current flows
Bulb condition	Does not glow	Glows

🎯 Exam Tip: In MP Board exams, questions on defining electric current and differentiating between open and closed circuits are common (1–2 marks). Always include the formula I = Q/t in your answer.

🔋 2. Electric Potential and Potential Difference

Electric Potential at a point is defined as the work done in bringing a unit positive charge from infinity to that point. Potential Difference (V) between two points is the work done in moving a unit charge from one point to the other.

Formula: V = W/Q where V = potential difference (V), W = work done (J), Q = charge (C)
1 volt = 1 joule / 1 coulomb

Voltmeter and Ammeter

Device	Measures	Connection	Unit
Ammeter	Current (I)	In series	Ampere (A)
Voltmeter	Potential Difference (V)	In parallel	Volt (V)

⚖️ 3. Ohm’s Law and Resistance

Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided physical conditions (temperature, pressure) remain constant. V ∝ I, or V = IR, where R is the resistance of the conductor.

Ohm’s Law Formula: V = IR where R = V/I
1 ohm (Ω) = 1 volt / 1 ampere

Factors Affecting Resistance

The resistance of a conductor depends on:

Length (l): R ∝ l — Longer wire has more resistance.
Cross-sectional area (A): R ∝ 1/A — Thicker wire has less resistance.
Material (resistivity ρ): Different materials have different resistivities.
Temperature: Resistance increases with temperature for conductors.

📘 Key Formula — Resistivity: ρ = R × A / l where ρ = resistivity (Ω-m), R = resistance (Ω), A = cross-sectional area (m²), l = length (m)
Unit of resistivity: ohm-metre (Ω-m)

Conductors, Insulators and Semiconductors

Type	Examples	Resistivity (Ω-m)
Conductors	Copper, Aluminium, Silver	10⁻⁸ to 10⁻⁶
Insulators	Rubber, Glass, Wood	10¹² to 10¹⁸
Semiconductors	Silicon, Germanium	10⁻⁶ to 10⁴

🎯 Exam Tip: In MP Board exams, Ohm’s law is asked every year — either as a direct definition question or in numerical form. Remember the V = IR formula and its graph (V vs I is a straight line through origin for ohmic conductors).

🔗 4. Series and Parallel Combination of Resistors

Resistors in Series

When resistors are connected end-to-end, they are said to be in series. The same current flows through each resistor, but the voltage divides.

Formula (Series): R_eq = R₁ + R₂ + R₃ + …
Current: Same through all resistors = I
Voltage: V = V₁ + V₂ + V₃ + …

Resistors in Parallel

When resistors are connected across the same two points, they are said to be in parallel. The same voltage is applied across each resistor, but the current divides.

Formula (Parallel): 1/R_eq = 1/R₁ + 1/R₂ + 1/R₃ + …
Voltage: Same across all resistors = V
Current: I = I₁ + I₂ + I₃ + …

Comparison: Series vs Parallel

Feature	Series	Parallel
Current	Same everywhere	Divides
Voltage	Divides	Same everywhere
Equivalent resistance	R_eq = R₁ + R₂ + … (increases)	1/R_eq = 1/R₁ + 1/R₂ + … (decreases)
If one bulb fails	Whole circuit breaks	Other bulbs keep glowing
House wiring uses	❌ Not used	✅ Used

🔥 5. Heating Effect of Electric Current

When an electric current passes through a conductor, the conductor gets heated due to the resistance it offers. This is called the heating effect of electric current. The heat produced (H) depends on the current (I), resistance (R), and time (t).

Joule’s Law of Heating: H = I²Rt where H = heat (J), I = current (A), R = resistance (Ω), t = time (s)

Applications of Heating Effect

Electric iron, heater, toaster: Use nichrome wire (high resistivity, high melting point).
Electric bulb: Tungsten filament (high melting point 3380°C) glows due to heating.
Electric fuse: Safety device — thin wire of low melting point that melts when current exceeds safe limit.

🎯 Exam Tip: The heating effect question appears regularly in MP Board exams (3–4 marks). Be ready to write Joule’s law, explain why nichrome is used in heaters, and explain electric fuse working.

💡 6. Electric Power and Commercial Unit

Electric Power is defined as the rate at which electrical energy is consumed or work is done by an electric circuit. It is measured in watts (W).

Power Formulas: P = VI = I²R = V²/R where P = power (W)
Energy: E = P × t Commercial unit: kilowatt-hour (kWh)
1 kWh = 3.6 × 10⁶ J

Power Rating of Common Appliances

Appliance	Power Rating (W)	Energy in 1 hour (kWh)
LED Bulb	10 W	0.01 kWh
Tube Light	40 W	0.04 kWh
Ceiling Fan	60–80 W	0.06–0.08 kWh
Electric Heater	1000–2000 W	1–2 kWh
Refrigerator	100–200 W	0.1–0.2 kWh

🧮 7. Important Numericals

Numerical 1: Ohm’s Law

Q: A potential difference of 12 V is applied across a resistor. If the current flowing through it is 2 A, find the resistance of the resistor.

Solution: Using V = IR → R = V/I = 12/2 = 6 Ω

Numerical 2: Series Combination

Q: Three resistors of 2 Ω, 3 Ω, and 5 Ω are connected in series. Find the total resistance and current if a 10 V battery is connected.

Solution: R_eq = 2 + 3 + 5 = 10 Ω. Current I = V/R = 10/10 = 1 A

Numerical 3: Parallel Combination

Q: Two resistors of 6 Ω and 3 Ω are connected in parallel. Find the equivalent resistance.

Solution: 1/R_eq = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 → R_eq = 6/3 = 2 Ω

Numerical 4: Heating Effect

Q: A 5 Ω resistor has a current of 2 A flowing through it for 10 minutes. Find the heat produced.

Solution: Using H = I²Rt = (2)² × 5 × (10 × 60) = 4 × 5 × 600 = 12,000 J

Numerical 5: Electric Power

Q: A 100 W bulb is used for 6 hours daily. Calculate the energy consumed in kWh in 30 days.

Solution: Energy per day = 100 W × 6 h = 600 Wh = 0.6 kWh. Total in 30 days = 0.6 × 30 = 18 kWh

🎯 Exam Tip: Numericals from Electricity carry 5–8 marks in MP Board exams. Practice all formula variations: V = IR, P = VI, H = I²Rt, and energy calculations in kWh.

📋 Previous Year Questions (2017–2026)

Year	Question	Marks
2024	State Ohm’s law and derive the relation V = IR.	3
2024	Two resistors of 4 Ω and 6 Ω are connected in parallel. Find the equivalent resistance.	2
2023	What is Joule’s law of heating? Write the formula and explain its applications.	4
2023	Define electric power. A bulb rated 60 W is used for 5 hours daily. Find the energy consumed in 30 days.	3
2022	State the factors on which the resistance of a conductor depends.	3
2022	Differentiate between series and parallel combination of resistors.	4
2021	Find the equivalent resistance when three resistors of 2 Ω, 3 Ω, and 5 Ω are connected in series.	2
2020	Explain the heating effect of electric current. Write any two applications.	3
2019	Calculate the resistivity of a wire of length 2 m, area 0.5 mm², and resistance 5 Ω.	3
2018	What is the commercial unit of electrical energy? Convert 1 kWh into joules.	2
2017	Define electric current. Write its SI unit and formula.	2

❓ Frequently Asked Questions

Q1. What is electric current? Write its SI unit.

Electric current is the rate of flow of electric charge through a conductor. Its SI unit is the ampere (A). One ampere is the flow of one coulomb of charge per second: 1 A = 1 C/s.

Q2. State Ohm’s law and write its mathematical expression.

Ohm’s law states that at constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. V ∝ I, or V = IR, where R is the resistance.

Q3. What is the difference between a conductor and an insulator?

Conductors allow electric current to flow through them easily (e.g., copper, aluminium), while insulators do not allow current to flow (e.g., rubber, plastic). Conductors have very low resistivity (10⁻⁸ Ω-m), while insulators have very high resistivity (10¹² Ω-m or more).

Q4. Why is tungsten used as the filament in electric bulbs?

Tungsten is used because it has a very high melting point (3380°C), which allows it to glow white-hot without melting. It also has high resistivity, producing sufficient heat and light when current passes through it.

Q5. Why is nichrome used in electric heaters and irons?

Nichrome (an alloy of nickel and chromium) has very high resistivity and a high melting point. It does not oxidise easily even at high temperatures, making it ideal for heating elements in electric heaters, irons, and toasters.

Q6. What is the function of an electric fuse in a circuit?

An electric fuse is a safety device that protects the circuit from excessive current. It contains a thin wire of low melting point. When current exceeds the safe limit, the fuse wire melts and breaks the circuit, preventing damage to appliances and fire hazards.

Q7. How is the resistivity of a material related to its resistance?

Resistivity (ρ) and resistance (R) are related by the formula: R = ρl/A, where l is the length and A is the cross-sectional area. Resistivity is a material property that does not depend on the dimensions of the conductor, while resistance depends on both material and dimensions.

Q8. What is the commercial unit of electrical energy? Convert it into joules.

The commercial unit of electrical energy is the kilowatt-hour (kWh). 1 kWh = 1 kW × 1 h = 1000 W × 3600 s = 3.6 × 10⁶ J. Electricity bills measure energy consumption in kWh.

Q9. Why are household appliances connected in parallel rather than in series?

Household appliances are connected in parallel because: (a) each appliance gets the same voltage (220 V), (b) each appliance can be switched on/off independently, and (c) if one appliance fails, others continue to work. In series, all appliances would share voltage and a single failure would break the entire circuit.

Q10. What is Joule’s law of heating? Write its formula.

Joule’s law of heating states that the heat produced in a conductor is directly proportional to the square of the current (I²), the resistance (R), and the time (t) for which current flows. Formula: H = I²Rt. Heat is measured in joules (J).

Q11. How much current will a 100 W bulb draw from a 220 V supply?

Using P = VI, we get I = P/V = 100/220 = 0.454 A. So a 100 W bulb draws approximately 0.45 A of current from a 220 V supply.

Q12. What is meant by 1 ohm? Define it.

One ohm is the resistance of a conductor through which a current of 1 ampere flows when a potential difference of 1 volt is applied across its ends. 1 Ω = 1 V / 1 A.

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