UPSC CSE Science and Technology Syllabus

What is the difference between renewable and non-renewable energy sources?

Renewable sources replenish naturally on a human timescale (solar, wind, hydro, biomass, geothermal). Non-renewable sources are finite and deplete with use (coal, oil, natural gas, nuclear fuels).

What is the photovoltaic effect that solar cells rely on?

The generation of voltage and electric current in a material (typically silicon) upon exposure to light, as photons knock electrons loose to create a flow of current across a p-n junction.

Name the main types of renewable energy and their primary source.

Solar (sunlight), Wind (moving air), Hydropower (flowing water), Biomass/Biofuel (organic matter), Geothermal (Earth's internal heat), and Tidal/Wave (ocean movement).

How does a wind turbine generate electricity?

Wind turns the turbine's blades (rotor), converting kinetic energy into rotational mechanical energy; this drives a generator that converts mechanical energy into electrical energy via electromagnetic induction.

What is the difference between solar thermal and solar photovoltaic (PV) technology?

Solar PV converts sunlight directly into electricity using semiconductor cells. Solar thermal captures the Sun's heat to warm a fluid, used for water heating or to produce steam that drives turbines (concentrated solar power).

What is biogas and what is its main component?

A renewable fuel produced by the anaerobic decomposition of organic matter (e.g., animal dung, crop waste). Its main combustible component is methane (CH4), typically 50-70%.

What is geothermal energy?

Energy derived from heat stored within the Earth, harnessed by tapping hot water or steam from underground reservoirs to generate electricity or for direct heating.

What is nuclear fission and what fuel commonly powers it?

The splitting of a heavy atomic nucleus (e.g., Uranium-235 or Plutonium-239) into lighter nuclei, releasing large amounts of energy and neutrons. Uranium-235 is the most common reactor fuel.

What is nuclear fusion and why is it harder to achieve than fission?

The joining of light nuclei (e.g., hydrogen isotopes deuterium and tritium) into a heavier nucleus, releasing energy - the process that powers the Sun. It requires extremely high temperatures and pressures to overcome nuclear repulsion, making it hard to sustain on Earth.

What is the role of a moderator in a nuclear reactor?

A moderator (e.g., heavy water, graphite, or light water) slows down fast neutrons to thermal speeds, increasing the probability they cause further fission and sustaining the chain reaction.

What is the role of control rods in a nuclear reactor?

Control rods (made of neutron-absorbing materials like boron or cadmium) absorb excess neutrons to regulate or shut down the fission chain reaction and control the reactor's power output.

What are the three stages of India's nuclear power programme?

Stage 1: Pressurised Heavy Water Reactors using natural uranium (produces plutonium). Stage 2: Fast Breeder Reactors using plutonium and producing U-233 from thorium. Stage 3: Reactors using the U-233/thorium cycle, leveraging India's large thorium reserves.

What is a nuclear chain reaction and what is 'critical mass'?

A self-sustaining series of fission reactions where neutrons released by one fission trigger further fissions. Critical mass is the minimum amount of fissile material needed to sustain such a chain reaction.

Why is thorium important for India's energy strategy?

India holds about one-quarter of the world's thorium reserves but limited uranium. Thorium (Th-232) can be converted to fissile Uranium-233 in breeder reactors, offering long-term fuel security (the basis of Stage 3).

What is energy conservation, and how does it differ from energy efficiency?

Energy conservation means reducing energy use by changing behavior or cutting consumption. Energy efficiency means achieving the same output using less energy through better technology (e.g., an LED bulb giving the same light as an incandescent with less power).

What does India's BEE Star Rating label indicate?

Issued by the Bureau of Energy Efficiency, the star label (1 to 5 stars) rates an appliance's energy efficiency - more stars mean lower energy consumption for the same performance.

Why are LED bulbs preferred over incandescent bulbs for energy conservation?

LEDs convert a far higher fraction of energy into light rather than heat, using roughly 80-90% less electricity and lasting much longer for the same brightness (luminous output).

What is the difference between primary and secondary energy?

Primary energy is found in nature before any conversion (crude oil, coal, sunlight, wind). Secondary energy is produced from primary sources through conversion (electricity, petrol, hydrogen).

What does the Internet's TCP/IP protocol suite do?

TCP/IP governs how data is packetized, addressed, transmitted, routed, and reassembled across networks. TCP ensures reliable, ordered delivery; IP handles addressing and routing of packets between hosts.

What is the difference between the Internet and the World Wide Web?

The Internet is the global network of interconnected computers (the infrastructure). The World Wide Web is a service running on the Internet - a system of interlinked hypertext documents accessed via browsers using HTTP.

What is an IP address, and how do IPv4 and IPv6 differ?

A unique numerical identifier for a device on a network. IPv4 uses 32-bit addresses (~4.3 billion addresses); IPv6 uses 128-bit addresses, providing a vastly larger address space to overcome IPv4 exhaustion.

What is DNS and what function does it perform?

The Domain Name System translates human-readable domain names (e.g., www.example.com) into machine-readable IP addresses, acting like the Internet's phonebook.

What is cloud computing? Name its three main service models.

Delivery of computing services (servers, storage, software) over the Internet on demand. Models: IaaS (Infrastructure as a Service), PaaS (Platform as a Service), and SaaS (Software as a Service).

What is the Internet of Things (IoT)?

A network of physical objects ('things') embedded with sensors, software, and connectivity that collect and exchange data over the Internet, enabling smart homes, wearables, and industrial automation.

What do the generations of mobile telecommunication 2G, 3G, 4G, and 5G primarily offer?

2G: digital voice and SMS; 3G: mobile data/web browsing; 4G LTE: high-speed broadband, video streaming; 5G: ultra-high speed, very low latency, and massive device connectivity for IoT.

What is the difference between analog and digital signals in telecommunication?

Analog signals are continuous waves representing data by varying amplitude/frequency. Digital signals represent data as discrete binary values (0s and 1s), offering better noise immunity and easier processing.

What is optical fibre communication and its key advantage?

Transmission of data as light pulses through thin glass/plastic fibres using total internal reflection. Advantages: very high bandwidth, low signal loss over long distances, and immunity to electromagnetic interference.

What is bandwidth in the context of data communication?

The maximum rate of data transfer across a network path, usually measured in bits per second (bps). Higher bandwidth allows more data to be transmitted in a given time.

What is the CIA triad in cyber security?

The three core principles of information security: Confidentiality (preventing unauthorized access), Integrity (ensuring data is accurate and unaltered), and Availability (ensuring authorized users can access resources when needed).

What is the difference between symmetric and asymmetric encryption?

Symmetric encryption uses a single shared key for both encryption and decryption (fast, e.g., AES). Asymmetric encryption uses a public/private key pair - one to encrypt, the other to decrypt (e.g., RSA), enabling secure key exchange.

What is a phishing attack?

A social-engineering cyberattack where attackers send fraudulent messages (often emails) impersonating a trusted source to trick victims into revealing sensitive data like passwords or financial details.

Differentiate a computer virus from a worm.

A virus attaches to a host file/program and needs user action to spread. A worm is standalone malware that self-replicates and spreads across networks automatically without needing a host file or user action.

What is a Distributed Denial of Service (DDoS) attack?

An attack that floods a server, service, or network with overwhelming traffic from many compromised systems (a botnet), exhausting resources so legitimate users cannot access it (attacking Availability).

What is ransomware?

Malicious software that encrypts a victim's files or locks their system, then demands payment (ransom), usually in cryptocurrency, in exchange for restoring access.

What is a firewall in network security?

A security system (hardware or software) that monitors and controls incoming and outgoing network traffic based on predefined rules, acting as a barrier between a trusted internal network and untrusted external networks.

What is two-factor authentication (2FA)?

A security method requiring two different forms of verification to access an account - typically something you know (password) plus something you have (a phone/OTP) or something you are (biometric).