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
Which of the following is NOT a property of a magnet?
Detailed Solution:
[CORE CONCEPT]: Magnets exhibit specific properties such as attraction to ferromagnetic materials (like iron) and the presence of a magnetic field. [STEP-BY-STEP SOLUTION]: While magnets attract iron and exhibit repulsion between like poles, they do not attract all metals (e.g., aluminum, copper). [SHORTCUT / EXAM TRICK]: Remember that only ferromagnetic materials are attracted to magnets. [COMMON MISTAKE TRAP]: Students may assume all metals are magnetic, leading to incorrect conclusions.
Question 2 of 5 Live App Practice
For an electric circuit given below, the correctcombination of voltage (V) and current (I) is
\[ I = I_1 + I_2 + I_3 = 3 + 1.5 + 1 = 5.5 \, A \]
📌 Hints / Properties Used:
Ohm's Law: \( V = IR \)
Current in parallel: \( I_{total} = I_1 + I_2 + I_3 \)
📊 Visual Diagram Suggestion:
A schematic showing the parallel connection of resistors with wires indicating current flows and labeled voltage sources to clarify voltage drops and current distribution.
📖 Factual Verification & Reference:
Verified against NCERT Class XII Physics, Chapter 12 (Current Electricity).
Question 3 of 5 Live App Practice
An incandescent electric bulb converts 20%of its power consumption into light and the remaining power is dissipated as heat. The bulb’s filament has a resistance of 200 W and 2 A current flows through it. If the bulb remains ON for 10 h and the rate of electricity chargeis ₹ 5/unit, then which among the followingis the correct amount of the money spent on producing light?
Detailed Solution:
Solution
Option (d) is correct.
Explanation:
\[ P = I^2R \]
Here, \( I = 2 \, \text{A} \) and \( R = 200 \, \Omega \).
A schematic circuit diagram representing the incandescent bulb, indicating the current and resistance values, along with power dissipation percentages would enhance comprehension.
📖 Factual Verification & Reference:
Verified against NCERT Class XII Physics, Chapter 4 (Electromagnetic Induction).
Question 4 of 5 Live App Practice
The AC mains domestic supply current in India changes direction in every:
Detailed Solution:
Correct Answer
✓ Option (d) is correct. AC current changes direction every 1/100 seconds.
📖 Governing Law / Core Concept
In alternating current (AC) systems, the frequency of the AC supply determines the time taken for the current to change direction. The formula for frequency (\( f \)) is given by:
\[ f = \frac{1}{T} \]
Where \( T \) is the time period in seconds. In India, the frequency of AC is 50 Hz.
🧪 Step-by-Step Breakdown
To calculate the time period \( T \) of the AC supply:
Option (a): 50 s - Incorrect; far too long for practical AC usage.
Option (b): 1/50 s - Incorrect; this would correspond to a higher frequency than typical AC.
Option (c): 100 s - Incorrect; outside the range of domestic supply.
Option (d): 1/100 s - Correct; matches the AC frequency in India.
⚡ Mnemonic / Speed-Run
Remember: For AC systems, frequency and time period are inversely related. 50 Hz translates to a direction change of 1/100 seconds.
6. Visual Suggestion
Include a cycle diagram illustrating the AC waveform, highlighting the direction change points every 1/100 seconds.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class 12 Physics, Chapter on Alternating Current.
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
