Posted by Chapter 3 of the RBSE Class 12 Physics syllabus, “Current Electricity,” explores the principles of electric current, resistance, and various laws related to the flow of electric charge. Understanding this chapter is vital as it forms the foundation for many practical applications in electronics, power distribution, and circuit analysis.
Table of Contents
Key Topics Covered in Chapter 3: Current Electricity
- Electric Current: Introduction to electric current, its definition, and understanding its relation to charge and time.
- Drift Velocity and Ohm’s Law: Understanding the flow of electrons in a conductor and the relationship between current, voltage, and resistance.
- Resistance and Resistivity: Exploring the factors affecting resistance and the concept of resistivity.
- Series and Parallel Combination of Resistors: Analyzing resistors connected in series and parallel and deriving formulas for total resistance.
- Electrical Power and Energy: Relationship between power, current, voltage, and energy consumption in electrical circuits.
- Kirchhoff’s Laws: Introduction to Kirchhoff’s current law (KCL) and Kirchhoff’s voltage law (KVL), crucial for solving complex electrical circuits.
- Internal Resistance of a Cell: Understanding how the internal resistance affects the efficiency of a battery or cell.
RBSE Solutions for Important Questions from Chapter 3
1. What is Electric Current? Define Its SI Unit.
Solution: Electric current is the flow of electric charge through a conductor. The electric current III is defined as the rate of flow of charge:[math]I=QtI = \frac{Q}{t}I=tQ[/math]
where [math]QQQ[/math] is the charge and ttt is the time.
SI Unit: The SI unit of electric current is the Ampere (A). One ampere is defined as one coulomb of charge passing through a conductor per second.
2. What is Ohm’s Law? Derive Its Mathematical Expression.
Solution: Ohm’s Law states that the current III flowing through a conductor is directly proportional to the potential difference [math]VVV[/math] and inversely proportional to the resistance RRR:I=VRI = \frac{V}{R}I=RV
where:
- III is the electric current (in amperes, A),
- [math]VVV [/math]is the potential difference (in volts, V),
- RRR is the resistance (in ohms, Ω).
Derivation: This law was experimentally verified by Georg Simon Ohm and is valid for materials that obey linear current-voltage characteristics, i.e., resistive materials.
3. Define Resistance and Resistivity.
Solution:
- Resistance: The resistance of a conductor is the opposition it offers to the flow of current. It is given by:[math]R=ρLAR = \rho \frac{L}{A}R=ρAL[/math]where[math]ρ\rhoρ [math]is the resistivity of the material, LLL is the length of the conductor, and AAA is the cross-sectional area.
- Resistivity: Resistivity [math](ρ\rhoρ)[math] is a property of a material that quantifies how strongly it resists current. It is measured in ohm-meters (Ω·m). Different materials have different resistivities.
4. What is Drift Velocity?
Solution: Drift velocity is the average velocity of charged particles (electrons) in a conductor under the influence of an electric field. It is given by:[math]vd=InAev_d = \frac{I}{nAe}vd=nAeI[math]
where III is the current, nnn is the number of free electrons per unit volume, AAA is the cross-sectional area, and eee is the charge of an electron.
Drift velocity is generally very small but is responsible for the flow of current in a conductor.
5. Derive the Formula for Power in an Electric Circuit.
Solution: The power PPP delivered to a resistor in an electric circuit is the rate at which energy is used or dissipated. It is given by:[math]P=VIP = VIP=VI[/math]
where:
- Pis the power (in watts, W),
- Vis the potential difference (in volts, V),
- I is the current (in amperes, A).
Using Ohm’s Law (V=IRV = IRV=IR), we can also express power in terms of current and resistance: [math]P=I2R=V2RP = I^2R = \frac{V^2}{R}P=I2R=RV2[/math]
These formulas are useful for calculating power in different electrical systems.
6. What are Kirchhoff’s Current and Voltage Laws?
Solution:
- Kirchhoff’s Current Law (KCL): The sum of currents entering a junction in an electric circuit is equal to the sum of currents leaving the junction. Mathematically: [math]∑Iin=∑Iout\sum I_{\text{in}} = \sum I_{\text{out}}∑Iin=∑Iout[math]
- Kirchhoff’s Voltage Law (KVL): The sum of the potential differences (voltage) around any closed loop in a circuit is zero. This law is based on the conservation of energy: [math]∑Vin=∑Vout\sum V_{\text{in}} = \sum V_{\text{out}}∑Vin=∑Vout[math]
These laws are fundamental tools for analyzing complex circuits and are widely used in circuit analysis.
7. What is the Effect of Connecting Resistors in Series and Parallel?
Solution:
Preparation Tips for Chapter 3: Current Electricity
- Understand the Fundamental Concepts: Make sure to grasp the basic principles such as electric current, drift velocity, and Ohm’s Law.
- Practice Numerical Problems: Work on problems involving calculations of power, resistance in series and parallel, and Kirchhoff’s laws.
- Master Kirchhoff’s Laws: These are essential for solving complex circuit problems. Practice applying KCL and KVL to various circuit configurations.
- Relate Theory to Practical Applications: Understand how resistivity, resistance, and Ohm’s law apply to everyday electronic devices like resistors, wires, and batteries.
- RBSE Solutions for Class 12 Physics Chapter 4 – Moving Charges and Magnetism
- RBSE Solutions for Class 12 Physics Chapter 3: Current Electricity
- RBSE Solutions for Class 12 Physics Chapter 2: Electrostatic Potential and Capacitance
- Rbse Class 12 Physics Chapter 1: Electric Charges and Fields Solution
FAQs on Current Electricity
What is the SI Unit of Electric Current?
The SI unit of electric current is the Ampere (A).
- What Happens to the Total Resistance When Resistors are Connected in Parallel?
- The total resistance decreases when resistors are connected in parallel because the current has multiple paths to flow through.
- What is the Relationship Between Power, Current, and Voltage?
- Power PPP is the product of current III and voltage VVV. It can also be expressed as [math]P=I2RP = I^2 RP=I2R or P=V2RP = \frac{V^2}{R}P=RV2.[/math]
- How Does a Battery’s Internal Resistance Affect the Circuit?
- A battery’s internal resistance reduces the effective voltage available to the external circuit and reduces the overall efficiency.
By understanding the key concepts and practicing related problems, students can confidently tackle problems related to “Current Electricity” in their RBSE Class 12 exams.
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