What is the Exam?
The Combined Defence Services (CDS) examination is a premier national-level competitive exam conducted biannually by the Union Public Service Commission (UPSC). It serves as a gateway for spirited and patriotic graduates to join the Indian Armed Forces as Commissioned Officers. Successful candidates are allocated to the Indian Military Academy (IMA) Dehradun, Indian Naval Academy (INA) Ezhimala, Air Force Academy (AFA) Hyderabad, and the Officers Training Academy (OTA) Chennai.
Among the various segments of the CDS written examination, the General Knowledge paper plays a decisive role in merit listing. Within this paper, General Science contributes a massive chunk of questions—often ranging from 28 to 32 questions out of 120. A significant majority of these science questions are directly rooted in the Class 10 National Council of Educational Research and Training (NCERT) curriculum, specifically focusing on fundamental concepts of Physics and Chemistry. For defence aspirants aiming to clear the stringent cut-offs, mastering the UPSC CDS general science physics chemistry class 10 notes is not just optional; it is an absolute necessity.
Key Highlights 2026
As we look toward the CDS 2027 cycle, staying updated with the operational and structural trends of the current year is vital for targeted preparation. Below are the key highlights concerning the examination ecosystem and the shifting trends in the science section.
- Conducting Body: Union Public Service Commission (UPSC).
- Exam Frequency: Twice a year (CDS I in April and CDS II in September).
- Focus Area for Science: Conceptual clarity over rote memorization. UPSC has shifted from purely factual questions to application-based problems rooted in Class 9 and 10 NCERT text.
- Physics Trends: An increase in numerical problems related to Optics (Lens and Mirror formulas) and Electricity (Resistor networks and Power dissipation).
- Chemistry Trends: Heavy emphasis on Chemical Reactions, Everyday Chemistry, pH values, and Metallurgy basics.
- Negative Marking: One-third ($0.33$) of the marks assigned to a question are deducted for every incorrect response.
- Mode of Exam: Offline (Pen and Paper-based) using Optical Mark Recognition (OMR) sheets.
Syllabus 2026
The General Science syllabus for the CDS exam is broadly aligned with the secondary school curriculum, but UPSC infuses a deeper analytical twist to the questions. The Class 10 Physics and Chemistry chapters form the absolute spine of this syllabus.
Here is a detailed breakdown of the high-yield topics from the Class 10 syllabus that routinely appear in the examination:
| Subject | Class 10 NCERT Chapter | Core Topics & High-Yield Sub-topics |
|---|---|---|
| Physics | Light - Reflection and Refraction | Laws of reflection, spherical mirrors, mirror formula, magnification, refractive index, refraction through glass slab, spherical lenses, lens formula, power of a lens. |
| Physics | The Human Eye and the Colorful World | Structure of the human eye, defects of vision (Myopia, Hypermetropia, Presbyopia) and their correction, atmospheric refraction, scattering of light (Tyndall effect, blue color of sky). |
| Physics | Electricity | Electric current, potential difference, Ohm's law ($V = IR$), factors affecting resistance, resistivity, series and parallel combination of resistors, heating effects of current ($H = I^2Rt$), electric power. |
| Physics | Magnetic Effects of Electric Current | Magnetic field lines, field due to a current-carrying conductor, straight wire, circular loop, and solenoid. Force on a current-carrying conductor, Fleming's Left-Hand Rule, Electric Motor, Electromagnetic Induction, Fleming's Right-Hand Rule, Domestic electric circuits. |
| Chemistry | Chemical Reactions and Equations | Writing balanced chemical equations, types of chemical reactions: combination, decomposition, displacement, double displacement, oxidation, and reduction (Redox reactions). Corrosion and rancidity. |
| Chemistry | Acids, Bases and Salts | Chemical properties of acids and bases, reaction with metals, carbonates, and hydrogen carbonates. Concept of pH scale ($pH = -\log[H^+]$), importance of pH in everyday life. Preparation and uses of Sodium Hydroxide, Bleaching Powder, Baking Soda, Washing Soda, and Plaster of Paris. |
| Chemistry | Metals and Non-Metals | Physical and chemical properties of metals and non-metals, reactivity series, ionic compounds (formation and properties), basic metallurgical processes (roasting, calcination), corrosion and its prevention. |
| Chemistry | Carbon and its Compounds | Covalent bonding in carbon compounds, versatile nature of carbon, homologous series, nomenclature of carbon compounds, chemical properties (combustion, oxidation, addition, substitution). Ethanol and Ethanoic acid properties, soaps, and detergents. |
Exam Pattern
To build an effective preparation blueprint, you must understand how the marks are distributed across different papers. The exam pattern varies depending on whether you are opting for the permanent commission wings (IMA, INA, AFA) or the short service commission wing (OTA).
For IMA, INA, and AFA
Candidates applying for the technical and traditional branches must appear for three distinct papers conducted on the same day.
| Paper Name | Duration | Number of Questions | Maximum Marks |
|---|---|---|---|
| English | 2 Hours | 120 | 100 |
| General Knowledge (including Science) | 2 Hours | 120 | 100 |
| Elementary Mathematics | 2 Hours | 100 | 100 |
| Total | 6 Hours | 340 | 300 |
For Officers Training Academy (OTA)
Candidates applying for OTA are exempted from the mathematics paper, making the General Knowledge paper exceptionally critical for their final merit.
| Paper Name | Duration | Number of Questions | Maximum Marks |
|---|---|---|---|
| English | 2 Hours | 120 | 100 |
| General Knowledge (including Science) | 2 Hours | 120 | 100 |
| Total | 4 Hours | 240 | 100 |
Note on Marking Scheme: In the General Knowledge paper, each question carries approximately $0.83$ marks ($100 \text{ marks} / 120 \text{ questions}$). An incorrect answer triggers a penalty of $1/3$ of the marks assigned to that question, which equates to roughly $-0.27$ marks per wrong answer.
Eligibility Criteria
Before diving deep into your academic notes, ensure that you fulfill the strict physical and educational parameters set by the UPSC. The criteria listed below are relevant for the upcoming cycles across 2026 and 2027.
1. Educational Qualifications
- For IMA and OTA: A recognized degree from a conventional university in any discipline (Arts, Commerce, Science, Management, etc.).
- For Indian Naval Academy (INA): A degree in Engineering from a recognized university or institution.
- For Air Force Academy (AFA): A degree from a recognized university (with Physics and Mathematics at the 10+2 level) or a Bachelor of Engineering/Technology.
2. Age Limit & Marital Status
- IMA: Unmarried male candidates aged between 19 and 24 years.
- INA: Unmarried male candidates aged between 19 and 24 years.
- AFA: 20 to 24 years. Upper age limit for candidates holding valid and current Commercial Pilot Licence issued by DGCA is relaxable up to 26 years (Unmarried).
- OTA (Men): Unmarried male candidates aged between 19 and 25 years.
- OTA (Women): Unmarried women, issueless widows who have not remarried, and issueless divorcees who have not remarried, aged between 19 and 25 years.
Application Process
The UPSC releases notifications for the CDS exam online through its official portal. Candidates must navigate the process carefully to avoid disqualification due to administrative errors.
- One-Time Registration (OTR): Candidates must first register themselves on the UPSC official OTR platform. This is a one-time process that saves basic demographic and academic details for all future UPSC applications.
- Filling Part-I of the Application Form: Log in using your OTR credentials and select the active CDS notification. Fill in your preferred choices of academies (IMA, INA, AFA, OTA) in order of preference.
- Application Fee Payment: Pay the online application fee of ₹200. Female candidates and SC/ST candidates are completely exempted from fee payment.
- Uploading Documents: Upload scanned copies of your photograph, signature, and an officially approved photo identity card (Aadhaar Card, Voter ID, PAN Card, Passport, etc.). Ensure the image resolutions comply strictly with UPSC guidelines.
- Center Selection and Part-II Submission: Choose your preferred examination city from the available slots. Check all entered data carefully, agree to the declaration, and hit submit to print your final application confirmation page.
Preparation Strategy
Cracking the General Science portion of the CDS exam demands an organized alignment between standard textbooks and objective-type practice patterns. Since Class 10 Physics and Chemistry hold immense leverage, follow this structured strategy to optimize your score.
1. Build Foundations with NCERTs
Do not start your preparation with thick, postgraduate reference books. Pick up the Class 9 and Class 10 NCERT Science textbooks. Read them line-by-line. Highlight critical definitions, chemical formulas, and boxes labeled "Do you know?". UPSC regularly lifts analytical statements straight out of these text boxes.
2. Master Numerical Applications in Physics
UPSC has increased the weightage of numerical problems. You must be comfortable applying foundational equations quickly during the exam. Memorize and practice formulas like:
- Mirror and Lens Formulas: $$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \quad \text{(Mirror)}$$ $$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \quad \text{(Lens)}$$
- Ohm's Law and Power: $$V = IR, \quad P = VI = I^2R = \frac{V^2}{R}$$
3. Develop Conceptual Chemistry Mindmaps
Chemistry in CDS focuses heavily on the practical properties of compounds. Create clean sheets containing all major chemical reactions from Class 10. Learn the specific industrial and household uses of compounds like Bleaching Powder ($CaOCl_2$), Baking Soda ($NaHCO_3$), and Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$). Understand the reactivity series of metals to easily solve single displacement reaction questions.
4. Solve Previous Years' Questions (PYQs)
Analyze the last 5 to 7 years of CDS GK papers. Look closely at how questions from the "Human Eye" or "Carbon and its Compounds" are framed. You will notice that while the facts remain constant, UPSC changes the phrasing to test whether your conceptual core is strong or if you have simply crammed the facts.
5. Take Timed Mock Tests regularly
Reading theory is only half the battle won; executing that knowledge under a ticking clock determines success. Incorporate Exam Bhai free mock tests into your weekly routine. These mock assessments simulate real exam conditions, help fine-tune your elimination techniques, and pinpoint whether you are losing marks to negative scoring in the general science portion.
Cut-Off Trends
To pass the written stage, a candidate must clear two separate thresholds: a minimum qualifying mark in each individual paper (usually 20%) and an aggregate cut-off score that fluctuates depending on the difficulty of the paper and total vacancies.
The historical written cut-off scores (out of total marks) generally follow the trends below:
| Academy Wing | Total Marks | Average Written Cut-Off Range |
|---|---|---|
| IMA | 300 | 125 – 135 |
| INA | 300 | 115 – 125 |
| AFA | 300 | 140 – 150 |
| OTA (Men & Women) | 200 | 95 – 105 |
Because the General Knowledge paper is traditionally considered a low-scoring module due to vast current affairs and humanities components, a high score in the General Science section (achieved by mastering Class 10 notes) acts as a structural booster. It helps push your cumulative total safely past these competitive thresholds.
Frequently Asked Questions
Q1: Is reading Class 10 NCERT alone enough to clear the Physics and Chemistry questions in CDS?
Ans: Yes, Class 10 NCERT along with Class 9 NCERT covers more than 85% of the Physics and Chemistry questions asked in the CDS GK paper. However, you must read them analytically. Pay attention to properties, conceptual explanations, and everyday examples provided in the textbook rather than just memorizing definitions.
Q2: What kind of numerical questions are asked from Class 10 Physics in the CDS exam?
Ans: The numerical questions are usually direct but require clear concepts. They predominantly feature calculation of focal length, image distance, and magnification using mirror or lens formulas. You will also find questions asking for equivalent resistance in series/parallel circuits, or calculating electrical energy consumption and power of domestic appliances.
Q3: How should I prepare the reactions given in Carbon and its Compounds for CDS?
Ans: Focus on the fundamental reactions given in the Class 10 textbook: combustion, oxidation, substitution, and addition reactions (like hydrogenation of vegetable oils). Additionally, pay close attention to the structural differences between saturated and unsaturated hydrocarbons and the working mechanism of soaps and detergents.
Q4: Does the CDS General Knowledge paper have sectional cut-offs, and how does science help?
Ans: Yes, there is a minimum qualifying threshold of 20% for each individual paper, which means you must score at least 20 marks out of 100 in the General Knowledge paper. Because history, geography, and current affairs can be vast and unpredictable, General Science provides concrete, formula-driven marks that help you safely clear this sectional benchmark.
Q5: What is the significance of the pH scale and chemical compounds in the CDS Chemistry section?
Ans: UPSC frequently creates matching or multiple-choice questions based on the pH values of common substances (like gastric juice, blood, lemon juice, and pure water). Questions regarding the chemical formulas, chemical names, and primary industrial applications of everyday salts like Baking Soda, Washing Soda, and Bleaching powder are regular features.
Q6: Where can I practice objective questions specifically tailored for CDS General Science?
Ans: Aside from reviewing past UPSC question papers, you can utilize the curated test modules on Exam Bhai. Practicing via Exam Bhai free mock tests gives you access to high-yield, Class 10-based questions designed strictly around the latest UPSC testing trends, enabling better self-assessment and time management.
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