Science & Technology — Latest Developments & Space

Why This Chapter Matters

Physics contributes four to six questions in SSC CGL Tier-1 General Awareness, and unlike history or polity, these questions test understanding, not just recall. A well-worded physics question can be answered from first principles even if you have forgotten the exact fact, which makes this the highest-leverage section in the whole GA syllabus: study it properly once, and you can solve variations you have never seen before.

The single biggest mistake aspirants make is memorising formulas without knowing what each quantity physically means. You can memorise "P = W/t" all you like, but if a question describes a scenario in words — a man climbing stairs, a bulb glowing, a spring stretching — and you cannot recognise which formula applies, the memorised symbol is useless. This chapter builds every concept from a real object you have touched: a cricket ball, a ceiling fan, a mirror, a battery. Read the analogies as seriously as the formulas; they are the bridge that lets you recognise a concept when it is dressed up in exam language.

1. Units and Measurements

Physics is the science of measurable quantities, and every measurable quantity needs a unit. The world settled on the SI system (Système International) built from seven base units.

Quantity	SI Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

Memory hook: "My Kind Sister Always Takes My Candies" gives Metre-Kilogram-Second-Ampere-Temperature(Kelvin)-Mole-Candela in order.

Every other unit is "derived" from these seven. Speed is metre per second (m/s), force is kg·m/s² (renamed the newton), and so on. Two quantity types matter for exams:

• Scalar quantities have only magnitude: mass, speed, distance, energy, temperature.
• Vector quantities have magnitude and direction: displacement, velocity, acceleration, force, momentum.

Exam trap: Speed and velocity sound interchangeable in daily speech but are not the same in physics. Speed is scalar (just "how fast"); velocity is vector (how fast, in which direction). A car going around a circular track at constant speed has changing velocity, because direction keeps changing. This exact distinction is a favourite trap in SSC papers.

Similarly, distance (scalar, total path covered) and displacement (vector, shortest straight-line change in position) differ. If you walk one full lap of a 400 m track and return to the start, your distance is 400 m but your displacement is zero.

2. Laws of Motion

Sir Isaac Newton gave three laws that describe how objects move and why they change motion, and SSC treats all three as must-know.

First Law (Law of Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by an external force. This is why passengers jerk forward when a bus brakes suddenly — your body was moving with the bus and "wants" to keep moving even though the bus has stopped; only the seatbelt or the seat in front supplies the force to stop you.

Second Law: Force equals mass times acceleration, written F = ma. A heavier object needs more force to achieve the same acceleration as a lighter one. This is why pushing an empty shopping trolley is easy and pushing one loaded with a sack of rice takes visibly more effort for the same speeding-up.

Third Law: For every action, there is an equal and opposite reaction. When you jump off a small boat onto a riverbank, the boat pushes back and drifts away from the bank — your push on the boat (action) is matched by the boat's push on you (reaction), in the opposite direction.

Memory hook: Inertia-Force-Reaction, or "Idiots Forget Reactions" — the initials I-F-R map to Laws 1-2-3 in order.

Momentum and Its Conservation

Momentum (p) = mass × velocity (p = mv). It is a vector quantity, and its SI unit is kg·m/s. The law of conservation of momentum states that in a closed system with no external force, total momentum before a collision equals total momentum after. This explains why a rifle recoils backward when fired: the bullet gains forward momentum, and the rifle must gain equal backward momentum to keep the total unchanged, even though the rifle barely moves compared to the bullet's speed (because it has far greater mass, so its velocity change is small).

Gravity and Weight

Gravitational acceleration (g) near Earth's surface is approximately 9.8 m/s². Mass is the amount of matter in an object and stays constant everywhere; weight is the force of gravity on that mass (Weight = mg) and changes depending on where you are. An astronaut has the same mass on the Moon as on Earth, but weighs about one-sixth as much, because the Moon's gravity is weaker.

Exam trap: Mass and weight are used interchangeably in casual conversation but tested as distinct concepts. Mass is measured in kilograms; weight, being a force, is technically measured in newtons, though everyday "weighing machines" report a mass-equivalent value in kg for convenience.

3. Work, Energy, and Power

Work is done when a force causes displacement in the direction of the force: W = F × d (Work = Force × distance moved in the direction of force). If you push a wall with all your strength and it does not move, you have done zero work in the physics sense, however tired you feel, because there is no displacement.

Energy is the capacity to do work, measured in the same unit as work, the joule (J). The two forms tested most are:

• Kinetic energy (KE): energy of motion, KE = ½mv². A speeding car has kinetic energy; double its speed and its kinetic energy quadruples, not doubles, because velocity is squared in the formula.
• Potential energy (PE): stored energy due to position or state, most commonly gravitational PE, PE = mgh (mass × gravity × height). Water stored in a hilltop dam has enormous potential energy, which converts to kinetic energy, and then to electricity, as it rushes down through turbines.

Law of conservation of energy: Energy can neither be created nor destroyed, only converted from one form to another. A pendulum swinging demonstrates this beautifully: at the highest point of its swing it has maximum PE and zero KE (momentarily at rest); at the lowest point it has maximum KE and minimum PE. The total stays constant if we ignore air resistance and friction.

Power is the rate of doing work: P = W/t, measured in watts (W), where 1 watt equals 1 joule per second. A more powerful machine does the same work in less time, not necessarily more total work. This is why a 1000-watt motor lifts a weight faster than a 100-watt motor, even if both eventually lift the same weight to the same height.

Memory hook: Think of energy as money in a bank account (a fixed total that only changes form — cash to fixed deposit to gold, never vanishing) and power as your spending rate (how fast you use that money) — the total money is conserved, but how fast you can spend it depends on the "power" of your spending.

4. Simple Machines

A simple machine is a device that changes the direction or magnitude of an applied force to make work easier, without reducing the total work done (ignoring friction). The six classical simple machines are: lever, wheel and axle, pulley, inclined plane, wedge, and screw.

Mechanical Advantage (MA) = Load / Effort, tells you how much a machine multiplies your force. A crowbar prying open a crate is a lever: a small force applied at the long end lifts a heavy load at the short end, because the pivot (fulcrum) sits closer to the load.

Levers come in three classes, based on the relative position of fulcrum, load, and effort:

• Class I: fulcrum between load and effort (a seesaw, a pair of scissors).
• Class II: load between fulcrum and effort (a wheelbarrow, a nutcracker).
• Class III: effort between fulcrum and load (a pair of tongs, a fishing rod, your own forearm lifting a weight, with the elbow as fulcrum).

Memory hook: "FLE, LFE, FEL" won't stick, so instead picture three real objects in order of familiarity: seesaw (fulcrum in middle) → wheelbarrow (load in middle) → forearm (effort in middle, your bicep pulls between the elbow and the hand).

An inclined plane (a ramp) lets you move a heavy object upward using less force over a longer distance, which is why loading a heavy fridge into a truck is done up a ramp rather than lifting it straight up. A pulley changes the direction of the force you apply, letting you pull down to lift something up, useful at a well or a construction site crane.

5. Heat and Thermodynamics Basics

Heat is a form of energy that flows from a hotter body to a colder one, always in that direction, never spontaneously the reverse — this one-way flow is the basis of the second law of thermodynamics. Temperature, unlike heat, measures how hot or cold something is, not the amount of energy it contains. A cup of tea and a swimming pool at the same temperature do not hold the same heat energy; the pool holds vastly more, because it has far more matter to hold that energy in.

Three temperature scales matter for exams:

Scale	Freezing point of water	Boiling point of water
Celsius	0°C	100°C
Fahrenheit	32°F	212°F
Kelvin	273 K (273.15 K precisely)	373 K

Conversion: °F = (°C × 9/5) + 32. Kelvin = °C + 273.

Exam trap: Absolute zero (0 K, approximately -273°C) is the theoretical temperature at which molecular motion stops entirely; it is not the same as 0°C, a mistake many students make when scanning options quickly.

Heat transfer happens in three modes:

• Conduction: heat travels through direct contact within a solid, molecule to molecule, without the material itself moving. A metal spoon left in hot tea gets hot at the handle, because heat conducts up through the metal.
• Convection: heat travels through the actual movement of a fluid (liquid or gas). A room heater warms a room by convection: hot air rises, cool air sinks to replace it, creating a circulating current.
• Radiation: heat travels as electromagnetic waves, needing no medium at all. This is how the Sun's heat reaches Earth across empty space, and why you feel heat from a bonfire even standing several feet away, with no air current between you and the flame carrying it.

Memory hook: Conduction needs Contact, Convection needs Currents (of fluid), Radiation needs no medium at all — three C-words for the first two, and the third stands apart because it alone crosses a vacuum.

6. Sound

Sound is a mechanical wave that requires a medium to travel; it cannot travel through vacuum, which is why explosions in outer space, however dramatic in films, would be silent in reality. Sound waves are longitudinal waves, meaning particles of the medium vibrate parallel to the direction the wave travels (unlike light, which is transverse).

Sound travels fastest in solids, slower in liquids, slowest in gases, because particles are packed most tightly in solids, allowing vibrations to pass from particle to particle with least delay. Roughly: sound in air travels around 343 m/s at room temperature, in water around 1,480 m/s, and in steel around 5,000 m/s.

Exam trap: Many students assume sound travels fastest through air since that is the medium we experience daily. It is the opposite: air, being a gas with loosely spaced molecules, is the slowest of the three states for sound transmission.

The audible range for humans is 20 Hz to 20,000 Hz (20 kHz). Sound below 20 Hz is infrasound (elephants and whales use this for long-distance communication); sound above 20 kHz is ultrasound (used in medical imaging, and by bats for echolocation).

7. Light: Reflection and Refraction

Reflection is the bouncing back of light when it hits a surface. The laws of reflection state that the angle of incidence equals the angle of reflection, and both rays lie in the same plane as the normal (the imaginary line perpendicular to the surface at the point of contact). A plane mirror produces an image that is virtual, erect, and laterally inverted (left-right reversed, which is why text held up to a mirror reads backward).

Refraction is the bending of light as it passes from one transparent medium to another with a different optical density, caused by a change in the light's speed. A pencil dipped in a glass of water appears bent at the surface, exactly because light bends as it moves from water to air (or air to water). Light bends toward the normal when entering a denser medium (air to water) and away from the normal when entering a rarer medium (water to air).

Two types of lenses matter for exams:

• Convex lens (converging lens): thicker at the centre, bends parallel light rays inward to a focal point. Used to correct hypermetropia (long-sightedness/farsightedness), where a person cannot see nearby objects clearly because the eye's lens focuses images behind the retina.
• Concave lens (diverging lens): thinner at the centre, spreads parallel light rays outward. Used to correct myopia (short-sightedness/nearsightedness), where distant objects appear blurred because the image forms in front of the retina.

Memory hook: Con-VEX helps you see things "next" to you far away, so it corrects the eye that cannot see far (hypermetropia needs a converging lens). Con-CAVE, like a cave, pulls the image "in" closer, correcting the eye that cannot see far (myopia) by diverging the rays before they overfocus. If that feels tangled, simplify with cause: myopia = image forms too early (in front of retina) = needs a lens that spreads light out first = concave. Hypermetropia = image forms too late (behind retina) = needs a lens that converges light sooner = convex.

Total internal reflection occurs when light travelling from a denser to a rarer medium hits the boundary at an angle greater than the critical angle, and instead of refracting out, it reflects entirely back into the denser medium. This is the principle behind optical fibre cables, which carry internet and telephone signals as pulses of light bouncing along the fibre's length without escaping.

The scattering of light explains two everyday sights: the sky appears blue because shorter wavelengths (blue) scatter more than longer wavelengths (red) when sunlight hits gas molecules in the atmosphere; sunsets appear red-orange because at that hour sunlight travels a longer path through the atmosphere, scattering away most blue light before it reaches your eyes, leaving mostly red and orange to arrive.

8. Electricity Basics

Electric current is the flow of electric charge, measured in amperes (A). Voltage (potential difference) is the "push" that drives current through a circuit, measured in volts (V). Resistance is opposition to current flow, measured in ohms (Ω).

Ohm's Law: V = IR (Voltage = Current × Resistance), valid at constant temperature for most conductors. Think of it like water flowing through a pipe: voltage is the water pressure, current is the flow rate, and resistance is how narrow the pipe is. A narrower pipe (higher resistance) reduces flow (current) for the same pressure (voltage).

Circuits come in two basic types:

• Series circuit: components connected end to end in a single loop; current is the same everywhere, but total resistance adds up, and if one component fails (like an old-style string of decorative lights), the entire circuit breaks.
• Parallel circuit: components connected across common points, each branch gets the same voltage; if one branch fails, others keep working, which is why household electrical wiring uses parallel circuits, letting you turn off one appliance without cutting power to the rest of the house.

Electric power: P = VI (Power = Voltage × Current), measured in watts, the same unit used for mechanical power, because both describe the rate of energy use regardless of the source.

Magnetism and Electromagnetism

A magnet has two poles, north and south, and like poles repel while unlike poles attract, mirroring how like charges repel and unlike charges attract in electrostatics. Hans Christian Oersted discovered in 1820 that an electric current produces a magnetic field around the wire carrying it, connecting electricity and magnetism as two faces of one phenomenon, now called electromagnetism.

This principle is used both ways in daily technology. An electromagnet (current creating magnetism) powers electric bells, cranes lifting scrap metal, and MRI machines. Electromagnetic induction (a changing magnetic field creating current), discovered by Michael Faraday, is the principle behind every electric generator, including the massive turbines at hydroelectric and thermal power plants that supply your home's electricity.

Memory hook: Oersted showed current makes magnetism; Faraday showed magnetism (changing) makes current. One discovery going forward, one coming back — together they form the two directions of the same street.

9. Modern Physics: Radioactivity and Nuclear Energy

Radioactivity is the spontaneous emission of radiation from unstable atomic nuclei, discovered by Henri Becquerel in 1896 while working with uranium salts, and studied extensively by Marie and Pierre Curie, who discovered the elements polonium and radium. Radioactive decay releases three types of radiation:

• Alpha particles: essentially helium nuclei (2 protons, 2 neutrons), positively charged, weakest penetrating power, stopped by a sheet of paper.
• Beta particles: high-speed electrons, negatively charged, moderate penetrating power, stopped by a few millimetres of aluminium.
• Gamma rays: high-energy electromagnetic radiation, no charge, strongest penetrating power, requires thick lead or concrete to stop.

Memory hook: Alpha is weakest, stopped by paper — think "A for A4 sheet." Gamma is strongest, needs a wall — think "G for Great thick wall."

Half-life is the time taken for half the atoms in a radioactive sample to decay. Each radioactive isotope has a fixed, unchanging half-life regardless of the sample's size or surrounding conditions. Carbon-14 dating uses the known half-life of carbon-14 (about 5,730 years) to estimate the age of organic archaeological remains, comparing the remaining radioactive carbon to the stable carbon in the sample.

Nuclear fission splits a heavy nucleus (like uranium-235) into two lighter nuclei, releasing large amounts of energy; this is the process used in nuclear power plants and atomic bombs. Nuclear fusion combines two light nuclei (like isotopes of hydrogen) into a heavier one, releasing even more energy per reaction than fission; this is the process that powers the Sun and all stars, and remains an active area of research for future clean energy on Earth.

Exam trap: Fission (splitting) is what current nuclear power plants use; fusion (combining) is what powers the Sun and is still largely experimental for commercial power generation on Earth. Do not swap which one is currently in commercial use.

India's civil nuclear power programme, run largely by the Nuclear Power Corporation of India Limited (NPCIL), operates plants such as Tarapur, Kudankulam, and Kaiga, using controlled nuclear fission to generate electricity, a small but steadily growing share of the country's power mix.

Quick Revision — One-Line Facts

1. SI base units: metre, kilogram, second, ampere, kelvin, mole, candela.
2. Speed is scalar; velocity is vector (same magnitude idea, but velocity needs direction).
3. Newton's First Law is the law of inertia; objects resist changes to their state of motion.
4. Newton's Second Law: F = ma.
5. Newton's Third Law: every action has an equal and opposite reaction.
6. Momentum = mass × velocity; total momentum is conserved in a closed system.
7. Gravitational acceleration near Earth's surface is about 9.8 m/s².
8. Mass is constant everywhere; weight (= mg) changes with gravitational field strength.
9. Work = Force × displacement in the direction of force; SI unit joule.
10. Kinetic energy = ½mv²; doubling velocity quadruples kinetic energy.
11. Potential energy (gravitational) = mgh.
12. Power = Work/time, SI unit watt (1 watt = 1 joule/second).
13. The six simple machines: lever, wheel and axle, pulley, inclined plane, wedge, screw.
14. Class I lever: fulcrum in middle (seesaw); Class II: load in middle (wheelbarrow); Class III: effort in middle (forearm).
15. Heat flows from hot to cold body only; this one-way rule underlies the second law of thermodynamics.
16. 0°C = 273 K = 32°F; absolute zero is 0 K, not 0°C.
17. Conduction needs contact, convection needs fluid movement, radiation needs no medium.
18. Sound is a longitudinal mechanical wave; it cannot travel through vacuum.
19. Sound travels fastest in solids, slower in liquids, slowest in gases.
20. Human audible range is 20 Hz to 20,000 Hz; below is infrasound, above is ultrasound.
21. Laws of reflection: angle of incidence equals angle of reflection.
22. A plane mirror image is virtual, erect, and laterally inverted.
23. Refraction bends light toward the normal when entering a denser medium.
24. Convex lens corrects hypermetropia (farsightedness); concave lens corrects myopia (nearsightedness).
25. Total internal reflection, used in optical fibres, occurs beyond the critical angle in a denser-to-rarer transition.
26. The sky is blue due to greater scattering of shorter (blue) wavelengths.
27. Ohm's Law: V = IR.
28. In a series circuit, one failure breaks the whole loop; in parallel, other branches keep working.
29. Oersted discovered current produces a magnetic field (1820); Faraday discovered electromagnetic induction.
30. Alpha particles are weakest (stopped by paper); gamma rays are strongest (need thick lead/concrete).
31. Half-life is the time for half a radioactive sample to decay; carbon-14 half-life is about 5,730 years.
32. Nuclear fission (splitting nuclei) powers current nuclear plants; fusion (combining nuclei) powers the Sun.

Memory Tables

Table 1: Key Formulas and Units

Concept	Formula	SI Unit
Force	F = ma	newton (N)
Momentum	p = mv	kg·m/s
Work	W = F × d	joule (J)
Kinetic Energy	KE = ½mv²	joule (J)
Potential Energy	PE = mgh	joule (J)
Power	P = W/t	watt (W)
Ohm's Law	V = IR	volt / ampere / ohm
Electric Power	P = VI	watt (W)

Table 2: Everyday Object to Physics Concept

Everyday Object/Event	Physics Concept
Bus braking suddenly, passenger jerks forward	Newton's First Law (inertia)
Rifle recoiling on firing	Conservation of momentum
Water stored in hilltop dam	Gravitational potential energy
Crowbar prying a crate open	Lever (simple machine)
Metal spoon heating up in hot tea	Conduction
Room heater warming a room	Convection
Feeling heat from a distant bonfire	Radiation
Pencil looking bent in a glass of water	Refraction
Text reading backward in a mirror	Lateral inversion (reflection)
Optical fibre carrying internet signal	Total internal reflection
Blue sky, red sunset	Scattering of light
Electric bell, MRI machine	Electromagnet
Hydroelectric power generator	Electromagnetic induction
Carbon dating of archaeological remains	Radioactive half-life

Practice MCQs

Q1. Which of the following is a vector quantity? (a) Speed (b) Mass (c) Velocity (d) Temperature

Q2. Newton's Third Law of Motion states that: (a) Objects at rest stay at rest unless acted upon by force (b) Force equals mass times acceleration (c) Every action has an equal and opposite reaction (d) Energy can neither be created nor destroyed

Q3. If the velocity of an object is doubled, its kinetic energy becomes: (a) Double (b) Half (c) Four times (d) Unchanged

Q4. The SI unit of power is: (a) Joule (b) Newton (c) Watt (d) Pascal

Q5. In which type of lever does the load lie between the fulcrum and the effort? (a) Class I (b) Class II (c) Class III (d) None of these

Q6. Absolute zero on the Kelvin scale corresponds to approximately: (a) 0°C (b) -100°C (c) -273°C (d) -373°C

Q7. Sound travels fastest in which medium? (a) Air (b) Water (c) Steel (d) Vacuum

Q8. A person suffering from myopia (short-sightedness) is prescribed which type of lens? (a) Convex lens (b) Concave lens (c) Cylindrical lens (d) Plano lens

Q9. Which scientist discovered that an electric current produces a magnetic field around a conductor? (a) Michael Faraday (b) Hans Christian Oersted (c) James Chadwick (d) Alessandro Volta

Q10. According to Ohm's Law, if resistance increases while voltage stays constant, current will: (a) Increase (b) Decrease (c) Remain the same (d) Become zero

Q11. Which type of radioactive radiation has the strongest penetrating power? (a) Alpha particles (b) Beta particles (c) Gamma rays (d) All are equal

Q12. Nuclear fusion, the process powering the Sun, involves: (a) Splitting a heavy nucleus into lighter ones (b) Combining light nuclei into a heavier one (c) Emission of alpha particles only (d) Conduction of heat through plasma

Q13. The human audible range of sound frequency lies between: (a) 2 Hz to 2,000 Hz (b) 20 Hz to 20,000 Hz (c) 200 Hz to 200,000 Hz (d) 20,000 Hz to 200,000 Hz

Q14. A pendulum at the lowest point of its swing has: (a) Maximum potential energy, zero kinetic energy (b) Maximum kinetic energy, minimum potential energy (c) Zero total energy (d) Equal kinetic and potential energy always

Q15. Which mode of heat transfer requires no medium at all? (a) Conduction (b) Convection (c) Radiation (d) All three require a medium

Answer Key

Q	Answer	One-line reason
1	(c) Velocity	Velocity has both magnitude and direction; speed, mass, and temperature are scalars.
2	(c) Every action has an equal and opposite reaction	This is Newton's Third Law; the first two options describe the First and Second Laws respectively.
3	(c) Four times	KE = ½mv² means kinetic energy scales with the square of velocity, so doubling v gives 4× KE.
4	(c) Watt	Power is the rate of doing work, measured in watts (1 watt = 1 joule/second).
5	(b) Class II	In a Class II lever like a wheelbarrow, the load sits between the fulcrum and the effort.
6	(c) -273°C	Absolute zero is 0 K, which converts to approximately -273°C, not 0°C.
7	(c) Steel	Sound travels fastest through solids because tightly packed particles transmit vibrations quickest.
8	(b) Concave lens	Myopia forms the image in front of the retina; a concave (diverging) lens pushes it back onto the retina.
9	(b) Hans Christian Oersted	Oersted's 1820 discovery linked electric current to magnetism, founding electromagnetism.
10	(b) Decrease	By V = IR, if V is constant and R increases, current I must decrease proportionally.
11	(c) Gamma rays	Gamma rays are high-energy electromagnetic radiation with the strongest penetrating power, needing lead or concrete to stop.
12	(b) Combining light nuclei into a heavier one	Fusion combines light nuclei (like hydrogen isotopes) and powers stars, unlike fission which splits heavy nuclei.
13	(b) 20 Hz to 20,000 Hz	This is the standard human audible frequency range; below is infrasound, above is ultrasound.
14	(b) Maximum kinetic energy, minimum potential energy	At the lowest point, height (and so PE) is minimum while speed (and so KE) is maximum.
15	(c) Radiation	Radiation travels as electromagnetic waves and needs no medium, unlike conduction and convection.