RRB NTPC Science Electricity Notes: Important Concepts, Formulas

RRB NTPC Science Electricity Notes: Electricity is one of the most crucial topics in the RRB NTPC Syllabus, and a strong grasp of its concepts can make a big difference in your exam score. From basic definitions of current, voltage, and charge to important formulas, units, and practical applications, electricity questions frequently appear in both numerical and theoretical sections. 

For aspirants aiming to secure high marks, understanding the topic thoroughly is essential. Here are comprehensive notes on electricity, including key concepts, step-by-step formulasand examples, to help you revise efficiently and boost your confidence before the exam.

What is Electricity?

Electricity, also known as current or electric flow, originates from charged particles. In simpler terms, it begins with a charged particle, usually an electron. However, it is specifically free electrons that carry the electric current through a conductor.

In any electric circuit:

• Electron flow direction is always opposite to the current direction.

• Current (I) is defined as the charge flowing per second in a circuit.

Formula for current:

I=tq​

Where:

𝐼

I = Current (Ampere)

𝑞

q = Charge (Coulomb)

𝑡

t = Time (seconds)

Unit of current: Ampere (A)

Unit of charge: Coulomb (C)

This foundational understanding is essential for solving numerical problems in RRB NTPC exams.

Detailed Notes of Electricity for RRB NTPC

A clear understanding of Electricity concepts not only helps in solving numerical problems but also boosts accuracy in theoretical questions. Here are key notes covering current, voltage, resistance, and their practical applications.

Electric Current

Electric current is the flow of electric charge. It is defined as the amount of charge flowing per unit time. Free electrons carry current in conductors. The direction of current is opposite to electron flow.

• Formula: I = Q/t

• Where I is current, Q is charge, and t is time.

• Unit: Ampere (A), which is Coulomb per second (C/s).

Electric Charge

Charge is a fundamental property of matter. Electrons carry negative charge. The charge is quantized.

• Electron Charge: e = 1.6 x 10^-19 C.

• Total Charge: Q = ne

• Where n is the number of electrons.

• Electrons in 1 Coulomb: Approximately 6 x 10^18 electrons.

Electric Potential and Voltage

Electric potential is the work done to move a unit positive charge from infinity to a point. Voltage (potential difference) is the work done per unit charge between two points.

• Formula: V = W/Q

• Where V is voltage, W is work, and Q is charge.

• Unit: Volt (V), which is Joule per Coulomb (J/C).

Measuring Instruments

Specific instruments measure electrical quantities.

Resistance and Resistivity

Resistance opposes the flow of current. Resistivity is an intrinsic property of a material.

• Resistance Formula: R = ρ L/A

• Where R is resistance, ρ is resistivity, L is length, and A is cross-sectional area.

• Factors Affecting Resistance: Length, area, temperature. Pressure does not affect resistance.

• Resistivity of Aluminium: Approximately 2.63 x 10^-8 Ω m.

• Effect of Stretching: If a wire stretches, its length increases, and cross-sectional area decreases. Both changes increase its resistance. This is a crucial concept for Railway NTPC Electricity Questions.

Kilowatt-hour (kWh)

Kilowatt-hour is the commercial unit of electrical energy.

• Definition: 1 kWh is the energy consumed by a 1 kilowatt appliance for 1 hour.

• Equivalence: 1 kWh = 1 unit of electricity.

Electric Power

Power is the rate at which work is done or energy is transferred.

• Formula: P = W/t

• Where P is power, W is work/energy, and t is time.

• Unit: Watt (W), which is Joule per second (J/s).

AC and DC

Current can flow in two main ways.

• Alternating Current (AC): Current direction reverses periodically. Household electricity is AC.

• Direct Current (DC): Current flows in one constant direction. Batteries supply DC.

Parallel Combination of Resistors

In a parallel circuit, total resistance decreases as more resistors are added. If parallel branches reduce, total resistance increases. For example, three 10 Ω resistors in parallel give 10/3 Ω. Two 10 Ω resistors in parallel give 5 Ω.

Key Mechanisms of Electricity

This section highlights important mechanisms and principles in electricity. These are crucial for understanding RRB NTPC Science MCQs.

Photovoltaic Effect

The photovoltaic effect converts light energy directly into electrical energy. Solar cells operate on this principle. It differs from the photoelectric effect, which involves electron emission from a metal surface due to light.

Mutual Induction

Mutual induction occurs when a changing current in one coil induces an electromotive force (EMF) in an adjacent coil. Transformers operate based on mutual induction. They efficiently transfer electrical energy between circuits.

Hydroelectric Power Plant Operation

Hydroelectric power plants convert water's potential energy into electrical energy. Falling water rotates turbines. These turbines then drive generators to produce electricity. This converts water energy to mechanical energy, then to electrical energy.

Fuse Wire Function

A fuse wire protects electrical circuits and appliances from overcurrent. It is an alloy of Lead and Tin. Fuse wires have a low melting point and high resistance. When current exceeds a safe limit, the fuse melts. This breaks the circuit, preventing damage.

Important Formulas of Electricity Chapter for RRB NTPC

Here is a list of key formulas of the Electricity Chapter for RRB NTPC exam preparation:

Preparation Tips for RRB NTPC Aspirants

Cracking the RRB NTPC exam requires a combination of smart study techniques, consistent practice, and time management. Aspirants often get overwhelmed due to the vast syllabus and negative marking in the exam. Here are actionable tips to help you prepare effectively:

• Focus on fundamental concepts rather than memorizing every formula.

• Practice previous year questions (PYQs), especially multiple-choice on electricity.

• Use tables and charts to memorize units and constants.

• Solve at least 20–30 numerical problems on current, voltage, and resistance.

• Make short notes on electron flow, AC/DC, solar cells, transformers, and hydroelectric generation.

By mastering these concepts, RRB NTPC aspirants can confidently answer conceptual, numerical, and theoretical questions related to electricity.

PW provides Railway exam content, including Railway Exam Blogs, sample papers, mock tests, guidance sessions, and more. Also, enroll today on Railway Online Coaching for preparation.