Home»NDA Physics»NDA Physics: Electricity, Magnetism & Ohm's Law
NDA Physics
NDA Physics: Electricity, Magnetism & Ohm's Law
By SenaPrep Defence Team Updated July 2026 8 min read
Cracking the UPSC National Defence Academy (NDA) written examination requires a highly focused preparation timeline. In this comprehensive study guide, our defence education experts analyze the core concepts of NDA electricity notes, resistance combinations GAT, Ohm's law formulas, outline high-yield preparation tips, and provide step-by-step examples.
Part 1: Physics core concepts & weightage
Physics contributes 23-25 questions in the General Science segment. Key areas include Mechanics, Properties of Matter, Oscillations/Waves, Optics, Heat/Thermodynamics, Electricity/Magnetism, and Modern Physics applications.
Syllabus Breakdown & Marks Allocation
Subject Segment
Total Questions
Weightage (Marks)
Preparation Priority
Paper 1: Mathematics
120 Questions
300 Marks
Critical (Sectional Cutoff)
Paper 2: GAT (English)
50 Questions
200 Marks
High Yield (4 Marks/Q)
Paper 2: GAT (General Knowledge)
100 Questions
400 Marks
High Scoring (Science & GS)
Part 2: Key Revision Strategies for NDA electricity notes, resistance combinations GAT, Ohm's law formulas
Success in this topic requires consistent daily practice. Here are the core routines recommended by top defence educators:
Build Foundational Concepts: Rely on Class 11 and 12 NCERT books for math/science topics, and read standard grammar texts for English.
Solve Previous Year Papers (PYQs): Go through at least the last 5-10 years of UPSC question sets to analyze repeat question structures.
Speed & Time Management: Practice mock tests with a timer to improve your answering speed. You have only 75 seconds per math question in the real exam.
Track Weak Areas: Bookmark difficult problems and review your mistake history to continuously raise your score.
Part 3: Practical Questions & Solved Examples
Below is a preview of the type of questions asked by the UPSC. Test your current understanding of NDA electricity notes, resistance combinations GAT, Ohm's law formulas and review the step-by-step methods:
Use the interactive test panel below to solve live questions pulled directly from the SenaPrep exam bank.
Interactive Practice Quiz
Test your preparation live! Choose an option for each question to see instant feedback and deep step-by-step explanations.
Question 1 of 5 Live App Practice
Consider the following part of an electric circuit :
The total electrical resistance in the given part of the electric circuit is
A clear schematic of the circuit showing the series and parallel arrangements of the resistors, labeling each with respective resistance values for clarity.
📖 Factual Verification & Reference:
Verified against NCERT Class XII Physics, Chapter 12 (Electricity).
Question 2 of 5 Live App Practice
If three resistors of 1 Ohm each, connect in parallel to each other, then resultant resistance is
Detailed Solution:
✓
1. Correct Answer
Option B is correct. The resultant resistance is 1/3 Ohm.
📖 Core Concept
In parallel circuits, the total resistance decreases as more resistors are added, calculated by summing the reciprocals of each individual resistor's resistance.
💡 3. Explanation
The formula for equivalent resistance \( R_{eq} \) for resistors in parallel is:
Use \( R_{eq} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \) for parallel resistances.
Understand that the equivalent resistance reduces when resistors are added in parallel.
📊 Visual Diagram Suggestion:
[Illustration showing three 1 Ohm resistors connected in parallel, indicating the effective resistance computation as \( \frac{1}{3}\, Ohm \)]
Question 3 of 5 Live App Practice
Which one of the following statements is NOT correct?
Detailed Solution:
✓
1. Correct Answer
Option D is correct. A voltmeter has low resistance, and an ammeter has high resistance is incorrect.
📖 Core Concept
Accurate measurement of electrical parameters requires ammeters and voltmeters to connect the circuit correctly based on their resistance characteristics.
💡 3. Explanation
An ammeter must be in series to measure current, having low resistance to avoid circuit disruption. A voltmeter requires parallel connection and has high resistance to prevent drawing significant current that would alter the voltage across the component.
❌ 4. Option Analysis
•Option A: Correctly states ammeters are connected in series.
•Option B: Correctly states voltmeters are connected in parallel.
•Option C: Correctly describes an ammeter's low resistance and a voltmeter's high resistance.
⚡
NDA Speed-Run / Mnemonic Shortcut
Remember: "Ammeters = Series + Low Resistance, Voltmeters = Parallel + High Resistance." This helps quickly recall their functions.
🎯
5. Key Takeaways
A voltmeter has high resistance and is used in parallel; an ammeter has low resistance and is used in series.
Question 4 of 5 Live App Practice
A current through a horizontal power line flow in east to west direction. What will be the direction of magnetic field at a point directly below when viewed from east end
Detailed Solution:
✓
1. Correct Answer
Option A is correct. The magnetic field direction is clockwise as observed from the east end of the wire.
📖 Core Concept
The direction of magnetic fields around current-carrying wires can be determined using the right-hand rule, which helps visualize their orientation in space.
💡 3. Explanation
The right-hand thumb rule states that if the thumb of the right hand points in the direction of the current (from east to west in this case), the direction in which the fingers curl gives the direction of the magnetic field lines.
\[ \text{Magnetic field direction} \rightarrow \text{Clockwise} \]
Therefore, at a point directly below the wire, when viewed from the east end, the magnetic field will indeed be in a clockwise direction in a plane perpendicular to the wire.
❌ 4. Option Analysis
•Option B: Anti-clockwise in a plane perpendicular to the wire - Incorrect because, based on the right-hand rule, the field is clockwise.
•Option C: Clockwise in a plane parallel to the wire - Incorrect; the observation is from below in a perpendicular plane.
•Option D: Anti-clockwise in a plane parallel to the wire - Incorrect since it misunderstands the trajectory of the magnetic field lines.
⚡
NDA Speed-Run / Mnemonic Shortcut
Use the right-hand rule by aligning the thumb with the current direction to quickly remember the magnetic field orientation.
🎯
5. Key Takeaways
Magnetic fields around current-carrying wires can be visualized using the right-hand rule; the field is clockwise when viewed from the east end.
Question 5 of 5 Live App Practice
If the length of a copper wire is increased by twice, then its resistivity will be
Detailed Solution:
✓
1. Correct Answer
Option C is correct. The resistivity of a material remains unchanged with length changes.
📖 Core Concept
Resistivity is a fundamental property of materials, independent of geometric attributes such as length or cross-sectional area.
💡 3. Explanation
Resistivity (\( \rho \)) is characterized by the formula:
\[ R = \rho \frac{L}{A} \]
where \( R \) is resistance, \( L \) is the length, and \( A \) is the cross-sectional area. Here, \( \rho \) is constant for a material under steady conditions and does not change regardless of the wire's length or shape. Therefore, increasing the length of the wire does not affect its resistivity.
❌ 4. Option Analysis
•Option A: Incorrect. Doubling the length influences resistance, not resistivity.
•Option B: Incorrect. Resistivity does not diminish with an increase in length.
•Option D: Incorrect. There is no correlation between the increase in length and resistivity.
⚡
NDA Speed-Run / Mnemonic Shortcut
Remember, resistivity (\( \rho \)) is solely a material characteristic and remains fixed regardless of length or shape variations.
🎯
5. Key Takeaways
Resistivity is unaffected by the wire's length or cross-sectional area.
Want to solve 10,000+ more questions?
Unlock full chapter tests, mock exams, real-time analytics, and our advanced AI doubt solver on the official SenaPrep Android app.
SENAPREP
