Understanding the intricacies of Current Electricity Mcq is pivotal for NEET aspirants aiming to secure top ranks. This chapter not only forms a significant portion of the Physics syllabus but also lays the groundwork for various medical technologies and diagnostics. In this guide, we’ll delve deep into the essential concepts, problem-solving techniques, and effective preparation strategies to master Current Electricity for the NEET examination.
Introduction to Current Electricity
Current Electricity pertains to the study of electric charges in motion, primarily focusing on the behavior of electrons in conductors. Unlike static electricity, where charges are stationary, current electricity deals with the continuous flow of electrons under the influence of an electric field.
Importance of Current Electricity in NEET
In the NEET Physics section, Current Electricity holds substantial weightage. Questions often test a candidate’s conceptual understanding and application skills, making it imperative to grasp the fundamentals thoroughly. A strong command over this topic can significantly boost your overall Physics score.
Fundamental Concepts of Electric Current
Definition and Nature of Electric Current
Electric current (I) is defined as the rate at which electric charge (Q) flows through a conductor’s cross-sectional area. Mathematically, it’s expressed as:
I=QtI = \frac{Q}{t}I=tQ
where ttt is the time in seconds. The unit of current is the Ampere (A), representing one coulomb of charge passing through a point per second.
Types of Electric Current
- Direct Current (DC): Flows uniformly in one direction. Common sources include batteries and DC power supplies.
- Alternating Current (AC): Changes direction periodically. Household power supplies typically provide AC.
Charge Carriers in Conductors
In metallic conductors, free electrons serve as the primary charge carriers. These electrons, delocalized from their parent atoms, move randomly in the absence of an electric field. When an external electric field is applied, they gain a net directional movement, constituting an electric current.
Drift Velocity and Its Significance
Understanding Drift Velocity
Drift velocity (vdv_dvd) refers to the average velocity attained by free electrons under an electric field. Despite their random thermal motion, the application of an electric field imparts a slight net velocity in a specific direction. It’s given by:
vd=InAev_d = \frac{I}{nAe}vd=nAeI
where:
- III = current
- nnn = number density of electrons
- AAA = cross-sectional area of the conductor
- eee = elementary charge
Relation Between Current and Drift Velocity
The electric current can also be expressed in terms of drift velocity:
I=nAevdI = nAev_dI=nAevd
This equation highlights that the current is directly proportional to the drift velocity, emphasizing the role of charge carrier density and conductor dimensions.
Ohm’s Law and Electrical Resistance
Statement of Ohm’s Law
Ohm’s Law establishes a linear relationship between the potential difference (V) across a conductor and the resulting current (I) flowing through it:
V=IRV = IRV=IR
Here, RRR denotes the resistance, a measure of the opposition to current flow.
Factors Affecting Resistance
Resistance depends on:
- Material’s Resistivity (ρ\rhoρ): Intrinsic property indicating how much the material opposes current.
- Length (L) of the Conductor: Resistance is directly proportional to length.
- Cross-sectional Area (A): Resistance is inversely proportional to the area.
The relationship is mathematically represented as:
R=ρLAR = \rho \frac{L}{A}R=ρAL
Temperature Dependence of Resistance
For most conductors, resistance increases with temperature. The temperature coefficient of resistance (α\alphaα) quantifies this change:
RT=R0[1+α(T−T0)]R_T = R_0 [1 + \alpha (T – T_0)]RT=R0[1+α(T−T0)]
where:
- RTR_TRT = resistance at temperature TTT
- R0R_0R0 = resistance at reference temperature T0T_0T0
Resistivity and Conductivity
Definition of Resistivity
Resistivity (ρ\rhoρ) is a material-specific property indicating how strongly it resists current flow. It’s expressed in ohm-meters (Ω·m).
Definition of Conductivity
Conductivity (σ\sigmaσ) is the reciprocal of resistivity:
σ=1ρ\sigma = \frac{1}{\rho}σ=ρ1
It measures a material’s ability to conduct electric current, with units of siemens per meter (S/m).
Combination of Resistors
Resistors in Series
When resistors are connected end-to-end:
- The total resistance (RsR_sRs) is the sum of individual resistances:Rs=R1+R2+R3+…R_s = R_1 + R_2 + R_3 + \ldotsRs=R1+R2+R3+…
- The current remains constant through all resistors.
- The voltage divides across each resistor proportionally.
Resistors in Parallel
When resistors are connected across the same two points:
- The reciprocal of the total resistance (RpR_pRp) is the sum of the reciprocals of individual resistances:1Rp=1R1+1R2+1R3+…\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldotsRp1=R11+R21+R31+…
- The voltage across each resistor remains the same.
- The current divides inversely proportional to the resistance values.
Electromotive Force (EMF) and Internal Resistance
Understanding EMF
Electromotive Force (EMF) is the potential difference generated by a source when no current flows. It’s the driving force that pushes electrons through a circuit, measured in volts (V).
Internal Resistance of Cells
Real batteries possess internal resistance (rrr) due to their internal components. The terminal voltage (VVV) of a cell supplying current (III) is:
V=E−IrV = \mathcal{E} – IrV=E−Ir
where E\mathcal{E}E is the EMF of the cell.
Kirchhoff’s Laws
Kirchhoff’s Current Law (KCL)
At any junction in an electrical circuit, the sum of currents entering equals the sum of currents leaving:
∑Iin=∑Iout\sum I_{\text{in}} = \sum I_{\text{out}}∑Iin=∑Iout
Kirchhoff’s Voltage Law (KVL)
The sum of all potential differences around any closed loop in a circuit equals zero:
∑V=0\sum V = 0∑V=0
These laws are instrumental in analyzing complex circuits.
Current Electricity Mcq for NEET
Basic Concepts of Electric Current
- The SI unit of electric current is:
a) Volt
b) Ohm
c) Ampere
d) CoulombAnswer: c) Ampere - If 3 C of charge flows through a conductor in 2 seconds, the current is:
a) 1.5 A
b) 3 A
c) 6 A
d) 0.67 AAnswer: a) 1.5 A - The flow of current in a metallic conductor is due to:
a) Protons
b) Neutrons
c) Free electrons
d) Positive ionsAnswer: c) Free electrons - Drift velocity of electrons is:
a) The speed of light
b) The random motion of electrons
c) The average velocity of electrons under an electric field
d) The velocity at which electrons leave the batteryAnswer: c) The average velocity of electrons under an electric field
Ohm’s Law and Resistance
- Ohm’s law is given by the equation:
a) V=IRV = IRV=IR
b) P=VIP = VIP=VI
c) R=V/IR = V/IR=V/I
d) I=VRI = VRI=VRAnswer: a) V=IRV = IRV=IR - The resistance of a wire is doubled when:
a) Its length is doubled
b) Its radius is doubled
c) Its cross-sectional area is doubled
d) Its resistivity is doubledAnswer: a) Its length is doubled - The unit of electrical resistance is:
a) Volt
b) Ampere
c) Ohm
d) FaradAnswer: c) Ohm - If the resistance of a wire is RRR, what will be the new resistance when its length is tripled and its cross-sectional area is halved?
a) 6R6R6R
b) 3R3R3R
c) 1.5R1.5R1.5R
d) 12R12R12RAnswer: d) 12R12R12R
Resistors in Series and Parallel
- The total resistance of three resistors R1,R2,R3R_1, R_2, R_3R1,R2,R3 in series is:
a) 1R1+1R2+1R3\frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}R11+R21+R31
b) R1+R2+R3R_1 + R_2 + R_3R1+R2+R3
c) R1×R2×R3R_1 \times R_2 \times R_3R1×R2×R3
d) R1R2R3R1+R2+R3\frac{R_1 R_2 R_3}{R_1 + R_2 + R_3}R1+R2+R3R1R2R3Answer: b) R1+R2+R3R_1 + R_2 + R_3R1+R2+R3 - When two resistors of 6 Ω and 12 Ω are connected in parallel, the equivalent resistance is:
a) 18 Ω
b) 4 Ω
c) 2 Ω
d) 8 ΩAnswer: b) 4 Ω
Electromotive Force and Internal Resistance
- A battery with an EMF of 12V and internal resistance of 1Ω supplies a current of 3A. The terminal voltage is:
a) 12V
b) 9V
c) 3V
d) 15VAnswer: b) 9V - The internal resistance of a cell is:
a) The resistance offered by external wires
b) The resistance due to electrolyte and electrodes
c) The resistance due to air
d) The resistance of the entire circuitAnswer: b) The resistance due to electrolyte and electrodes
Kirchhoff’s Laws
- Kirchhoff’s Current Law (KCL) states that:
a) The sum of potential differences in a closed loop is zero
b) The sum of currents entering a junction equals the sum of currents leaving
c) Resistance is proportional to voltage
d) Power is the product of current and voltageAnswer: b) The sum of currents entering a junction equals the sum of currents leaving - Kirchhoff’s Voltage Law (KVL) is based on:
a) Conservation of charge
b) Conservation of mass
c) Conservation of energy
d) Newton’s lawsAnswer: c) Conservation of energy - In a circuit, the total current entering a junction is 5A. If two wires carry 2A and 1A away from the junction, what is the current in the third wire?
a) 2A
b) 3A
c) 1A
d) 5AAnswer: a) 2A
Power and Energy in Electrical Circuits
- The power dissipated in a resistor of resistance RRR when a current III flows through it is:
a) P=IRP = IRP=IR
b) P=I2RP = I^2 RP=I2R
c) P=V/IP = V/IP=V/I
d) P=V2/IP = V^2/IP=V2/IAnswer: b) P=I2RP = I^2 RP=I2R - The unit of electrical power is:
a) Joule
b) Watt
c) Ampere
d) CoulombAnswer: b) Watt - A 60W bulb operates at 220V. The current flowing through it is:
a) 0.27 A
b) 0.55 A
c) 2.2 A
d) 4.4 AAnswer: a) 0.27 A
High-Level Conceptual MCQs
- A wire carries a steady current. Which of the following statements is true?
a) The drift velocity of electrons increases with time
b) The electric field inside the wire is zero
c) The number of electrons entering and leaving the wire per second is the same
d) The wire gains charge continuouslyAnswer: c) The number of electrons entering and leaving the wire per second is the same - Superconductors have:
a) Zero resistance
b) High resistance
c) Infinite resistance
d) Constant resistanceAnswer: a) Zero resistance
Conclusion
Mastering Current Electricity is crucial for NEET aspirants, as it lays the foundation for understanding electrical circuits and their applications in medical and diagnostic equipment. Concepts such as Ohm’s Law, Kirchhoff’s Laws, Resistance, EMF, and Power Dissipation frequently appear in NEET Physics questions, making it essential to have a clear and thorough understanding of these topics.
To excel in NEET Physics, focus on:
✅ Understanding the Core Concepts – Do not just memorize formulas; understand their derivations and applications.
✅ Solving Numerical Problems – Practice different types of numerical problems to enhance problem-solving speed.
✅ Practicing MCQs Regularly – Attempt as many multiple-choice questions as possible, especially previous year’s NEET questions.
✅ Referring to Reliable Study Materials – Follow NEET coaching materials like NEET World for expert guidance and structured learning.
A strategic approach, consistent practice, and conceptual clarity will help you ace Current Electricity in the NEET exam. Stay focused, practice diligently, and success will follow! 🚀
Frequently Asked Questions (FAQs)
1. Why is Current Electricity an important topic for NEET?
Answer: Current Electricity is a fundamental topic in NEET Physics that frequently appears in exams. It is essential for understanding electrical circuits, medical diagnostic tools, and practical applications in medical science. Mastering this topic can help boost your overall Physics score.
2. What are the most important formulas in Current Electricity for NEET?
Answer: Some key formulas to remember include:
- Ohm’s Law: V=IRV = IRV=IR
- Drift Velocity: vd=InAev_d = \frac{I}{nAe}vd=nAeI
- Resistance Formula: R=ρLAR = \rho \frac{L}{A}R=ρAL
- Power Dissipation: P=VI=I2R=V2RP = VI = I^2R = \frac{V^2}{R}P=VI=I2R=RV2
- Series Resistance: Rs=R1+R2+R3+…R_s = R_1 + R_2 + R_3 + \dotsRs=R1+R2+R3+…
- Parallel Resistance: 1Rp=1R1+1R2+1R3+…\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \dotsRp1=R11+R21+R31+…
3. How can I improve my problem-solving skills in Current Electricity?
Answer: To improve problem-solving skills:
- Practice a variety of numerical problems from different sources.
- Use previous NEET question papers to understand the exam pattern.
- Time yourself while solving questions to enhance speed and accuracy.
- Understand concepts deeply rather than relying on rote memorization.
4. What is the difference between EMF and Terminal Voltage?
Answer:
- Electromotive Force (EMF) is the total voltage produced by a cell or battery when no current is flowing.
- Terminal Voltage is the voltage available across the battery terminals when the circuit is complete and current is flowing. It is given by:
V=E−IrV = \mathcal{E} – IrV=E−Ir
where E\mathcal{E}E is the EMF, III is the current, and rrr is the internal resistance of the cell.
5. What are some common mistakes students make in Current Electricity?
Answer: Some common mistakes include:
- Confusing series and parallel resistance formulas.
- Incorrectly applying Kirchhoff’s Laws in complex circuits.
- Forgetting that drift velocity is very small despite a high current.
- Misinterpreting power formulas when using different expressions like P=VIP = VIP=VI, P=I2RP = I^2RP=I2R, and P=V2RP = \frac{V^2}{R}P=RV2.
- Neglecting the concept of internal resistance when calculating terminal voltage.
By avoiding these mistakes and following a structured study plan, you can confidently tackle Current Electricity questions in NEET and score high in the Physics section!
