NCERT Solutions for Class 10 Science Chapter 11: Electricity

Electricity is one of the most fundamental and scoring chapters in the CBSE Class 10 Science curriculum. From understanding how your household appliances function to grasping the complex concepts of potential difference and resistance, this chapter lays the groundwork for your future studies in physics. Because this topic carries significant weightage in board exams, mastering the numerical problems and theoretical definitions is essential.

If you are just starting your preparation or need a quick refresher on the core concepts before diving into the problems, check out our full chapter notes for a concise breakdown of Ohm’s law, resistivity, and heating effects of electric current. To ensure you stay on track with the official NCERT syllabus, these solutions are structured to align perfectly with the textbook’s requirements.

In-Text Questions and Solutions

Understanding Electric Current and Potential Difference

Q: What does an electric circuit mean? A: An electric circuit is a continuous and closed path of an electric current. It typically consists of a source of electricity (like a cell or battery), a switch, a load (like a bulb or resistor), and connecting wires.

Q: Define the unit of current. A: The SI unit of electric current is the Ampere (A). One Ampere is defined as the flow of one coulomb of charge through a conductor in one second (1 A = 1 C/s).

Q: Calculate the number of electrons constituting one coulomb of charge. A: We know that $Q = ne$, where $Q = 1$ C and $e = 1.6 \times 10^{-19}$ C. $n = Q / e = 1 / (1.6 \times 10^{-19}) = 6.25 \times 10^{18}$ electrons.

Resistance and Ohm’s Law

Q: On what factors does the resistance of a conductor depend? A: The resistance ($R$) of a conductor depends on:

• Length ($l$): Resistance is directly proportional to the length.
• Area of cross-section ($A$): Resistance is inversely proportional to the area.
• Material of the conductor: Represented by resistivity ($\rho$).
• Temperature: Resistance generally increases with temperature in metallic conductors.

Q: Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why? A: Current flows more easily through the thick wire. Since resistance is inversely proportional to the area of cross-section ($R \propto 1/A$), a thicker wire has less resistance, allowing more current to pass.

Numerical Problems on Series and Parallel Circuits

Q: An electric lamp of 100 $\Omega$, a toaster of resistance 50 $\Omega$, and a water filter of resistance 500 $\Omega$ are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Step-by-step working:

1. Since the appliances are in parallel, the total resistance ($R_p$) is: $1/R_p = 1/100 + 1/50 + 1/500$ $1/R_p = (5 + 10 + 1) / 500 = 16 / 500$ $R_p = 500 / 16 = 31.25 \Omega$
2. Total current ($I$) = $V / R_p = 220 / 31.25 = 7.04$ A.
3. The electric iron must have the same resistance as the equivalent resistance of the parallel combination to draw the same current. Thus, the resistance of the iron is 31.25 $\Omega$ and the current is 7.04 A.

For more practice on these complex calculations, you can browse all chapter notes available on our portal to strengthen your foundation.

Heating Effect of Electric Current

Q: Why does the cord of an electric heater not glow while the heating element does? A: The heating element has high resistance, which causes significant heat dissipation (Joule’s heating, $H = I^2Rt$) when current flows through it. The connecting cord has very low resistance, so it produces negligible heat and does not glow.

Q: An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case?

Step-by-step working:

• Case 1 (Max): $I = P/V = 840/220 = 3.82$ A. $R = V^2/P = (220)^2 / 840 = 57.62 \Omega$.
• Case 2 (Min): $I = P/V = 360/220 = 1.64$ A. $R = V^2/P = (220)^2 / 360 = 134.44 \Omega$.

Tips to Score Full Marks in Physics

1. Master the Units: Always write the SI units for your final answers. Losing half a mark for missing 'Amperes' or 'Ohms' is a common mistake.
2. Standardize Diagrams: When drawing circuits, use a sharp pencil and a scale. Label the ammeter (positive to positive) and voltmeter (parallel connection) correctly.
3. Practice Numericals Daily: Physics is about application. Use practice tests to time yourself and ensure you can solve problems under exam-like pressure.
4. Formula Sheet: Keep a sheet of all formulas ($V=IR$, $P=VI$, $H=I^2Rt$, etc.) on your desk. Refer to it while solving textbook exercises.
5. Check CBSE Guidelines: Always cross-verify your conceptual understanding with the official CBSE website to stay updated with the latest exam pattern.

Frequently Asked Questions

Q: Is it necessary to memorize all the definitions in Chapter 11? A: Yes, conceptual clarity is vital. You don't need to rote-learn, but you must be able to define terms like Electric Potential and Resistivity in your own words accurately.

Q: Are numericals more important than theory in this chapter? A: It is a balance. Usually, 40-50% of the marks in this chapter come from numerical problems, while the rest test your understanding of electrical components and circuits.

Q: How do I handle parallel vs series combination questions? A: Remember: In series, current remains the same; in parallel, voltage remains the same. Use these two rules to solve almost any circuit problem.

Q: Where can I find more solved examples? A: You can explore our extensive library of NCERT solutions to find step-by-step breakdowns of every exercise in your textbook.

Q: Can I use short-cut methods in the board exam? A: It is highly recommended to show all steps. Step-marking is a significant part of CBSE evaluation, and showing your working ensures you get credit even if you make a calculation error at the end.

Final Thoughts

Electricity is a scoring chapter once you understand the logic behind the formulas. By focusing on the relationship between current, voltage, and resistance, you can solve any problem thrown your way. Remember, consistency is the key to mastering physics. If you are looking for more resources, explore CircleOfLearning to discover a wide variety of subjects and topics tailored to help you excel in your board exams.

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