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DRDO runs two structurally different hiring pipelines - a GATE-based route for Scientist ‘B’ graduate/postgraduate entries via RAC, and a separate own-exam route for non-gazetted technical posts (STA-B, Technician-A) via CEPTAM.
Interview experience
DRDO interview experiences covering GATE score shortlisting (Scientist ‘B’ / RAC route), Written/descriptive test (some advertisements, RAC route), Personal Interview (RAC route), Computer-Based Test - CBT (CEPTAM route, non-gazetted posts), +2 more. Round-wise notes, common questions, and what candidates report clears each stage.
HR interview questions
DRDO HR interview questions with sample answer frameworks - motivation, relocation, STAR stories, and culture-fit prompts.
| Round | Duration | What it tests |
|---|---|---|
| GATE score shortlisting (Scientist ‘B’ / RAC route) | - | Valid GATE score in the matching discipline |
| Written/descriptive test (some advertisements, RAC route) | Varies | Core subject depth beyond GATE screening |
| Personal Interview (RAC route) | 30-45 min | Technical depth, defence-tech awareness, project discussion |
| Computer-Based Test - CBT (CEPTAM route, non-gazetted posts) | Multi-tier | General awareness, reasoning, quantitative aptitude, trade/technical knowledge |
| Trade/Skill Test (CEPTAM route) | Varies | Hands-on trade proficiency |
| Document verification & medical | - | Eligibility documents, category certificates, physical fitness |
Scientist ‘B’ hiring through RAC has no DRDO aptitude test, so these are the questions people ask about the GATE route and the interview. They are compiled from Physics Wallah’s summaries of RAC Advt. 156 (May 2025) and of DRDO recruitment through GATE, plus candidate reports on GeeksforGeeks, DipsLab and LinkedIn; the RAC advertisement for your cycle is final.
| Question | Answer |
|---|---|
| Is GATE required? | Yes, for Scientist ‘B’ through RAC. Shortlisting is on a valid GATE score in the discipline the advertisement maps to your degree. |
| Is there a DRDO written test? | Not in the 2025 cycle. Physics Wallah’s summary of Advt. 156 lists only GATE shortlisting and an interview. Some older advertisements added a descriptive test for particular disciplines. |
| What was the latest advertisement? | Advt. 156, published 30 May 2025, for 152 Scientist ‘B’ posts plus 3 added by addendum; applications closed 31 July 2025. As of Physics Wallah’s September 2026 page, no newer advertisement had been published. |
| Does it have negative marking? | Only in GATE itself. RAC adds no negative-marked MCQ paper on this route. |
| How much is the cutoff? | Not fixed. RAC sets a discipline-wise, category-wise GATE shortlist for each advertisement, about 1:10 against posts. |
| What is the eligibility? | First-class B.E./B.Tech. (or first-class Master’s for science posts) plus a valid GATE score in the mapped paper. Age limit 35 in Advt. 156, with relaxations. Pay Level 10, basic Rs 56,100. |
| How is the final merit calculated? | 80% GATE and 20% interview, per Physics Wallah’s Advt. 156 summary. One selected candidate reported GATE 844/1000, interview 70/100 and a final 81.52, which matches that split. Candidate write-ups also cite a minimum interview score, often 70 for UR and 60 for reserved categories; we could not confirm this in an official source. |
| What is the interview like? | A five-member panel, 30 to 80 minutes, often with a digital tablet for writing answers. You name 3 to 5 favourite subjects and the panel drills them, then strays into others. |
| Is there coding? | Short programs for CSE candidates, written on the tablet: matrix rotation, square root, partitioning a 0/1 array, primes up to 1000. No online coding test. |
These are questions candidates have reported for Scientist ‘B’ panels; they show the level, not a fixed list.
| Branch | Reported questions and topics |
|---|---|
| Computer Science | OSI vs TCP/IP, how a VPN works, security and cryptography follow-ups. Semaphores, deadlock, host vs guest OS. Phases of a compiler. Ternary vs binary search and its recurrence. Queue to stack conversion. Regression vs acceptance testing. Eigenvalues, Cayley-Hamilton and probability for candidates who list maths. |
| Electrical / Electronics | What GPS is, how it works and how many satellites it uses. Which effect radar uses (Doppler). Types and principles of induction and synchronous motors. Hilbert transform and its uses. Draw a half-wave rectifier. Op-amp circuits. Three-pin socket and multimeter basics. |
| Mechanical | Few detailed public reports. Expect GATE-depth core subjects you list, plus manufacturing basics (one electrical candidate was asked shaping vs milling machines). |
Asked across every branch: a brief introduction, your favourite subjects, a practical you performed in B.Tech, your project or thesis, why DRDO, and for working candidates, why you are leaving your current employer.
DRDO’s Scientist ‘B’ recruitment via RAC starts with shortlisting purely on your GATE score in the relevant engineering or science discipline - there’s no separate DRDO screening test at this stage.
Common questions
Some RAC advertisements add a written or descriptive test for particular disciplines before the interview, going deeper into core subject fundamentals than GATE’s objective format allows. The 2023-2024 candidate reports we found, and Physics Wallah’s summary of the 2025 advertisement, went straight from GATE shortlist to interview, so check whether your advertisement lists one.
Common questions
The closing stage for RAC-route candidates: a panel interview covering core technical depth, awareness of DRDO’s programmes and defence-technology areas, and a detailed walkthrough of your final-year project or thesis.
Common questions
Sample answer frameworks are on the DRDO HR interview questions page.
For non-gazetted technical posts like Senior Technical Assistant-B and Technician-A, CEPTAM runs its own Computer-Based Test - typically across multiple tiers - covering general awareness, reasoning, quantitative aptitude, and trade or technical knowledge specific to the post. Candidates who clear the CBT move to a hands-on Trade/Skill Test.
Common questions
DRDO isn’t one hiring pipeline - it’s two, run by different internal bodies. RAC handles gazetted Scientist posts (Scientist ‘B’ and above) through GATE-based shortlisting, a written test only where the advertisement adds one, and an interview. CEPTAM handles non-gazetted technical and support posts (STA-B, Technician-A, and similar) through its own Computer-Based Test and Trade/Skill Test, with no GATE requirement. Applying to the wrong prep track - say, GATE-focused prep for a CEPTAM CBT, or trade-syllabus prep for a Scientist ‘B’ interview - wastes real time, so confirm which recruitment body your target post falls under before you start.
Competitor notes stress GATE oral panels and lab awareness, not startup LLD.
Framework: Scientist B via GATE and RAC panel is different from CEPTAM or NATS apprenticeship. Read the advertisement name.
Framework: Name four subjects and expect depth; panels also probe subjects you avoided. Bring GATE-level clarity.
Framework: Problem, method, result, limitation. Defence application awareness without classified claims.
Framework: Specific lab or domain interest, willingness for non-metro lab cities, Indian citizenship and age criteria per advt.
The monostatic radar range equation gives received power as Pr = Pt * G^2 * lambda^2 * sigma / ((4*pi)^3 * R^4), where Pt is transmitted power, G antenna gain, lambda wavelength, sigma the target radar cross section and R the range. Because the signal spreads on the way out and again on the way back, received power falls as the fourth power of range. Solving for maximum range at a fixed minimum detectable signal means R_max varies as the fourth root of Pt, so doubling transmitter power buys only about 19 percent more range. That is why radar designers prefer higher antenna gain, pulse compression and coherent integration over brute-force power.
A ballistic missile is rocket-powered only during a short boost phase, after which it follows an unpowered ballistic trajectory shaped by gravity and drag, often leaving and re-entering the atmosphere; it flies high and fast and is used for long-range strike. A cruise missile uses an air-breathing engine such as a turbojet, turbofan or ramjet for the whole flight, stays within the atmosphere, and flies a low, terrain-following path with aerodynamic lift from wings. Cruise missiles are harder to detect because of that low flight profile and can manoeuvre and re-target in flight; ballistic missiles trade that for speed and range. BrahMos is a ramjet-powered supersonic cruise missile, while the Agni series is ballistic.
An INS uses accelerometers and gyroscopes to measure specific force and angular rate, then integrates them to propagate position, velocity and attitude from a known starting state. It is fully self-contained and cannot be jammed or spoofed, which matters for defence platforms, but sensor bias and noise are integrated too, so position error drifts and grows with time. Satellite navigation gives bounded absolute position error but is weak under jamming and has low update rates and outages. Fusing the two in a Kalman filter lets the satellite fix continuously estimate and correct INS bias and drift while the INS bridges outages, giving both short-term stability and long-term accuracy.
Carbon-fibre composites give very high specific strength and specific stiffness - strength and modulus divided by density - so a structure of equal load capacity weighs substantially less than an aluminium one, and every kilogram saved on a missile becomes range or payload. Their properties are anisotropic, so the laminate stack-up can be tailored to place fibres along the principal load paths. They also resist fatigue and corrosion far better than aluminium alloys. The trade-offs are poor through-thickness strength, vulnerability to barely visible impact damage and delamination, difficult non-destructive inspection, and much higher manufacturing cost.
Radar cross section is reduced mainly by shaping and by material choice. Shaping uses flat, canted surfaces and aligned planform edges to reflect incident energy away from the transmitter rather than back to it, and eliminates strong returns such as right-angle corner reflectors, exposed engine faces and external stores. Radar-absorbent materials add a lossy layer - typically ferrite or carbon-loaded - that converts incident energy into heat, and impedance-matched coatings cancel the surface reflection. Because monostatic detection range varies as the fourth root of RCS, cutting RCS by a factor of 10000 cuts detection range only by a factor of 10, which is still operationally decisive.
Engineering stress is load divided by the original cross-sectional area and engineering strain is elongation divided by the original gauge length, while true stress and true strain use the instantaneous area and length. Up to yield the two curves are nearly identical, but after necking the engineering curve turns down because the area shrinks while the original area is still used in the denominator, whereas the true stress curve keeps rising. The yield point marks the end of elastic behaviour and the start of permanent plastic deformation; for materials without a sharp yield, the 0.2 percent offset proof stress is used instead. Static design is normally carried out against yield strength with a factor of safety, not against ultimate tensile strength.
The Nyquist-Shannon theorem states that a signal band-limited to B hertz can be reconstructed exactly from uniform samples taken at a rate strictly greater than 2B. If the sampling rate is lower, frequency components above half the sampling rate fold back into the baseband and appear as false lower-frequency components - aliasing - which is irreversible once it has happened. In a radar receiver this shows up as ambiguous Doppler or range measurements: a target whose Doppler shift exceeds half the pulse repetition frequency is reported at the wrong velocity. Remedies are an analogue anti-aliasing filter ahead of the ADC, a higher sampling or pulse repetition frequency, or deliberate PRF staggering to resolve the ambiguity.
A solid motor stores fuel and oxidiser pre-mixed in a cast grain inside the casing, so it is mechanically simple, storable for years and can be launched at very short notice - which is why tactical and strategic missiles favour it. Once ignited, though, it burns to completion: thrust is set by the grain geometry and cannot be throttled or shut down and restarted. A liquid engine feeds separate fuel and oxidiser through pumps or pressurised tanks into a combustion chamber, so it can be throttled, stopped and restarted and generally gives higher specific impulse, at the cost of turbopumps, valves, plumbing and cryogenic handling. Hybrid motors pair a solid fuel with a liquid or gaseous oxidiser to get partial throttling with less complexity.
Only in GATE itself - RAC shortlists Scientist B candidates on GATE score and runs no negative-marked test of its own on that route (GATE deducts one-third of the marks for a wrong MCQ). Where an advertisement adds a descriptive written test for a discipline, it is not an MCQ paper.
There is no fixed cutoff; RAC sets a discipline-wise and category-wise GATE shortlist for each advertisement, at about 1:10 against posts. Physics Wallah’s summary of RAC Advt. 156 (2025) gives final merit as 80% GATE and 20% interview, which candidate-reported marks also fit, so a high GATE score still matters after the interview.
It depends on the post: DRDO runs two different recruitment routes. For Scientist ‘B’ (the main entry for engineering/science graduates and postgraduates, via the Recruitment & Assessment Centre/RAC): 1. Shortlisting on your GATE score in the matching discipline. 2. In some older advertisements and disciplines, a descriptive written test after shortlisting; the 2025 advertisement (Advt. 156) as summarised by Physics Wallah and recent candidate reports go straight from GATE score to interview. 3. A Personal Interview. For non-gazetted technical/admin posts like Senior Technical Assistant-B or Technician-A (via CEPTAM): DRDO’s own Computer-Based Test (CBT, often in two tiers), followed by a Trade/Skill Test, document verification, and medical exam - no GATE requirement at all.
Both, for different posts - GATE for Scientist ‘B’ and CEPTAM’s own CBT for non-gazetted posts. Scientist ‘B’ - the main graduate-entry technical role - is recruited primarily through GATE score shortlisting via RAC, sometimes with an added written test depending on discipline. Non-gazetted technical and support posts (Senior Technical Assistant-B, Technician-A, and similar CEPTAM-recruited roles) don’t use GATE at all - they’re filled through DRDO’s own multi-tier Computer-Based Test plus a Trade/Skill Test.
For Scientist ‘B’ interviews: core subject questions from your GATE-syllabus discipline, defence-technology and DRDO-programme awareness questions, and detailed cross-questioning on your final-year project or thesis. For CEPTAM technical-post selection, the CBT covers general awareness, reasoning, quantitative aptitude, and trade/technical knowledge, followed by a hands-on trade or skill test relevant to the post.
For Scientist ‘B’ via RAC: GATE-score shortlisting, then (only where the advertisement adds one) a written test, then a Personal Interview - so two or three real stages depending on the advertisement. For CEPTAM technical/support posts: a multi-tier Computer-Based Test, a Trade/Skill Test, document verification, and a medical exam - with no GATE or scientist-style interview involved.
If you’re targeting Scientist ‘B’, prioritise a strong GATE score in your discipline first, then revise core subject fundamentals at GATE depth for the written test and interview, and prepare a clear narrative on your final-year project since panels probe it closely. If you’re applying for a CEPTAM technical post (STA-B, Technician-A), focus on general aptitude, reasoning, and your specific trade syllabus for the CBT, and practice the hands-on skill test relevant to your trade.
RAC (Recruitment & Assessment Centre) handles DRDO’s gazetted Scientist posts - Scientist ‘B’ and above - largely through GATE score shortlisting. CEPTAM (Centre for Personnel Talent Management) handles non-gazetted technical and administrative posts like Senior Technical Assistant-B and Technician-A through DRDO’s own Computer-Based Test and trade/skill tests. They’re separate recruitment bodies with completely different selection processes, so check which one your target post falls under before you prep.
Yes - Scientist B cycles shortlist using GATE scores as per the RAC advertisement, then conduct a panel interview. Always follow the current official notification.
Not LeetCode-style, but CSE panels do ask short programs - for example rotating a matrix, finding a square root or partitioning a 0/1 array - written on a tablet, with complexity. Panels are mainly GATE-depth oral in your discipline plus project discussion.
Good fit: You like deep core subjects, you can live with a lab city that is not always a metro product office, and you can explain a project without slides.
Harder path: You only grind DSA; you want a 20 LPA product CTC; you applied to JTO and Scientist B with the same PDF; you cannot name one DRDO lab in your discipline.
Use this as a default four-week loop before a DRDO drive. Adjust to your invite timeline.
10-day crash version: Days 1-4 timed DSA, days 5-7 resume projects + CS fundamentals, days 8-9 mock interviews out loud, day 10 HR STAR stories on the HR page.
Candidate-reported packages for Scientist ‘B’ (Level 10) often cite ~₹8–12 LPA all-in, city-dependent, on top of a ₹56,100 basic scale frequently mentioned in offer discussions. Treat forum numbers as ranges, not guarantees - confirm the written appointment letter for your lab and city.
Interview process details and sample questions on this site are editorially organized from public candidate reports and hiring write-ups, with round structure, prep notes, and company-specific framing added by our team. For round-by-round stories, see the DRDO interview experience page. For OA papers and coding drills, use DRDO on placementpapers.app. Recruitment quick answers and FAQs draw on Physics Wallah’s DRDO Scientist B recruitment (Advt. 156) and DRDO recruitment-through-GATE pages. Branch-wise questions draw on the GeeksforGeeks DRDO Scientist B (RAC New Delhi, 2023) interview experience, the DipsLab DRDO electrical interview account and the LinkedIn candidate reports compiled on our DRDO interview experience page.
