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By Shailendra Singh
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Updated on 5 Nov 2025, 19:00 IST
Electrostatics and Electricity form a fundamental chapter in Class 10 CBSE Physics, covering the behaviour of charges at rest and in motion. This comprehensive guide consolidates all essential concepts, formulas, definitions, and practice questions to help students master Chapter 12 effectively.
Understanding electric charge, current, potential difference, resistance, and power is crucial not only for board exams but also for building a strong foundation for higher physics studies.
The study of electricity dates back to 600 B.C. when Thales of Miletus discovered that rubbing amber with wool attracted light objects like feathers. The Greek word for amber, elektron, gave rise to terms like electricity, electron, and electric charge.
Key Contributors:
| Term | Definition |
| Electric Charge | The property of matter that causes electrical and magnetic effects |
| Electrification | The phenomenon of charging a body by adding or removing electrons |
| Static Electricity | Electricity due to stationary charges on insulating surfaces |
| Electrostatics | The branch of physics dealing with charges at rest |
| Conductors | Materials that allow electric charges to flow freely (e.g., metals) |
| Insulators | Materials that do not allow charges to pass through them (e.g., rubber, glass) |
| Electric Current | The rate of flow of electric charge through a conductor |
| Potential Difference | Work done per unit charge in moving a charge between two points |
| Resistance | The opposition offered by a conductor to the flow of current |
| Ohm's Law | The current through a conductor is directly proportional to the potential difference across it |
| Formula Name | Mathematical Expression | Explanation |
| Electric Current | I = Q/t | Current equals charge flowing per unit time |
| Ohm's Law | V = IR | Potential difference equals current times resistance |
| Resistance | R = ρl/A | Resistance depends on length, area, and resistivity |
| Series Resistance | R_eq = R₁ + R₂ + R₃ + ... | Total resistance is sum of individual resistances |
| Parallel Resistance | 1/R_eq = 1/R₁ + 1/R₂ + 1/R₃ + ... | Reciprocal of equivalent resistance |
| Electric Power | P = VI = I²R = V²/R | Rate of energy consumption or production |
| Electrical Energy | U = Pt = VIt = I²Rt | Total energy consumed over time |
| Joule's Law of Heating | H = I²Rt | Heat produced by current in a conductor |
| Coulomb's Law | F = k(q₁q₂)/d² | Force between two point charges |
| Drift Velocity | I = neAvd | Current in terms of electron drift velocity |
Where:
The electric current flowing through a metallic conductor is directly proportional to the potential difference applied across its ends, provided the temperature remains constant.
Mathematical Form: V = IR
V-I Graph: A straight line passing through the origin with slope equal to resistance R.
When current flows through a resistor, heat is produced: H = I²Rt joules
Applications:
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NEET
Foundation JEE
Foundation NEET
CBSE
Question: A potential difference of 12V is applied across a resistor of 4Ω. Find the current.
Solution Steps:
Question: Three resistors of 2Ω, 3Ω, and 5Ω are connected in series. Find equivalent resistance.
Solution Steps:
Question: Two resistors of 6Ω and 3Ω are connected in parallel. Find equivalent resistance.
Solution Steps:
Quick formula for two resistors: R_eq = (R₁ × R₂)/(R₁ + R₂) = (6×3)/(6+3) = 18/9 = 2Ω
Question: A 100W bulb is used for 5 hours. Calculate energy consumed in kWh.
Solution Steps:
Question: A current of 5A flows through a 10Ω resistor for 2 minutes. Calculate heat produced.
Solution Steps:
1. The SI unit of electric charge is:
Answer: C) Coulomb
2. 1 Coulomb of charge is equivalent to the charge carried by:
Answer: A) 6.25 × 10¹⁸ electrons
3. The device used to measure electric current is:
Answer: B) Ammeter
4. An ammeter should be connected in a circuit:
Answer: A) In series
5. Ohm's law is not applicable to:
Answer: D) Vacuum tubes (Non-ohmic devices)
6. When two resistors are connected in series, the equivalent resistance is:
Answer: D) Both B and C
7. The resistivity of a conductor depends on:
Answer: C) Material and temperature
8. The commercial unit of electrical energy is:
Answer: C) Kilowatt-hour
9. A fuse wire is made of an alloy of:
Answer: C) Tin and copper (low melting point)
10. Which of the following does NOT represent electrical power?
Answer: D) IR²
Statement: The algebraic sum of currents at any junction in a circuit is zero.
ΣI = 0 (or) Incoming current = Outgoing current
Basis: Law of conservation of charge
Statement: The algebraic sum of potential differences in any closed loop is zero.
ΣV = 0 (or) Σε = ΣIR
Basis: Law of conservation of energy
A fuse is a protective device with a wire of low melting point (usually tin or tin-copper alloy) connected in series with the circuit.
How it works:
Types:
Rating: Fuse wires are rated by maximum current they can carry (e.g., 5A, 15A)
| Appliance | Typical Rating |
| LED Bulb | 7-15W |
| CFL | 15-25W |
| Incandescent Bulb | 60-100W |
| Tube Light | 40W |
| Ceiling Fan | 75W |
| Electric Iron | 1000W |
| Room Heater | 2000W |
| Water Heater | 2000W |
Confusing series and parallel formulas
Wrong unit conversions (kW to W, hours to seconds) Not converting time to seconds in heat calculations
Forgetting to square current in P = I²R
Using wrong formula for resistance (R = ρl/A, not R = lρA)
Mastering Electrostatics and Electricity requires a clear understanding of fundamental concepts, regular practice of numerical problems, and familiarity with formulas. This chapter forms the basis for understanding advanced topics in electricity and electronics in higher classes.
Notes:
Regular revision using the one-page sheet, solving MCQs, and practicing numericals will ensure excellent performance in board exams
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Charge (Q) is a property of matter measured in coulombs. Current (I) is the rate of flow of charge, measured in amperes (I = Q/t).
Because multiple paths are available for current flow, reducing overall opposition.
No, copper has a high melting point. Fuse wire must have a low melting point to melt quickly when excess current flows.
Since R = ρl/A, resistance becomes 4 times (doubled due to length, doubled again due to halved area).
Electric current passing through the body can disrupt heart rhythm, cause burns, and damage nerves. Always follow safety precautions.
The fundamental difference between AC (Alternating Current) and DC (Direct Current) lies in the direction and magnitude of electron flow. In DC current, electrons flow in a single, constant direction from the negative terminal to the positive terminal of a power source, such as a battery or cell. The magnitude of DC current remains constant over time, making it ideal for applications requiring steady voltage and current levels. Common sources of DC include batteries, solar cells, and DC power supplies used in electronic devices like mobile phones, laptops, and LED lights.
In contrast, AC current involves electrons that periodically reverse their direction of flow, typically in a sinusoidal pattern. The voltage and current in AC vary with time, oscillating between positive and negative values at a specific frequency (50 Hz in India, 60 Hz in the USA). This alternating nature makes AC current highly efficient for long-distance power transmission because it can be easily stepped up or down using transformers, minimizing energy loss during transmission. Our household electrical supply operates on AC current at 220-240V. The key advantage of AC over DC for power distribution is that transformers can change AC voltage levels efficiently, whereas DC voltage transformation is more complex and expensive.
The choice between AC and DC depends on the application. DC is preferred for battery-operated devices, electronic circuits, and applications requiring precise voltage control. AC dominates power generation and distribution systems due to its efficiency in transmission over long distances and the ease with which voltage levels can be modified. Understanding this distinction helps students appreciate why batteries provide DC while wall outlets provide AC, and why devices like phone chargers contain adapters to convert AC to DC for electronic components that require stable, unidirectional current flow.
Household electrical appliances are connected in parallel rather than in series for several critical practical and safety reasons. The most important reason is that parallel connection ensures each appliance receives the full supply voltage (220V in most countries) regardless of how many other devices are operating simultaneously. In a parallel circuit, all components are connected across the same two points, creating multiple pathways for current flow. This means your refrigerator, television, fan, and lights all operate at the rated voltage they're designed for, ensuring optimal performance and preventing damage that could occur from insufficient voltage.
In a series connection, the supply voltage would be divided among all connected appliances according to their resistances. This would mean that as you switch on more devices, the voltage across each device would decrease, causing them to operate inefficiently or not at all. For example, if you connected three 100W bulbs in series across a 220V supply, each would receive only about 73V instead of the rated 220V, causing them to glow very dimly. Moreover, in a series circuit, all devices must be switched on together, and if one appliance fails or is switched off, the entire circuit breaks, and all other devices stop working. Imagine if turning off your bedroom light caused your refrigerator to stop working—this would be completely impractical for household use.
Parallel connection offers the crucial advantage of independent operation. Each appliance can be switched on or off individually using its own switch without affecting other devices. Additionally, if one appliance fails or its fuse blows, other appliances continue to function normally because current can still flow through alternative parallel paths. The total current drawn from the main supply is the sum of individual currents through each appliance, which is why circuit breakers and fuses are rated according to the maximum expected total current. This configuration also allows for flexible power consumption—you can use any combination of appliances simultaneously based on your needs, making parallel connection the universal standard for residential and commercial electrical installations worldwide.