Physics
🔒 Log in to trackSI units and instruments, laws of motion, gravitation, fluids, heat, sound, light, electricity, EM waves, nuclear physics and famous inventions. CGL asks 1-2 questions — mostly units, instruments and 'which principle explains this everyday effect'.
One page per subtopic: detailed notes, every question type, formulas, tricks and practice sets.
Every formula on one printable page, grouped by subtopic.
4 exam-level questions worked step by step.
121 questions — untimed practice or a timed test with analysis.
Track record in the exam
Questions per shift in recent SSC CGL papers.
Test difficulty mix (121 questions)
Question patterns exams keep repeating
Taken from previous-year papers. If a pattern is marked "very common", expect to see it in your exam.
SI unit of a quantity
very common'The SI unit of magnetic flux / pressure / power of a lens is …', or a wrong-pair question mixing base and derived units.
How to solve: Learn the seven base units (m, kg, s, A, K, mol, cd) and the scientist-named derived units: newton, joule, watt, pascal, hertz, coulomb, volt, ohm, weber, tesla. Kill the traps: light year measures distance, kWh measures energy.
Example: The SI unit of magnetic flux is:
Weber (Wb). Magnetic flux density (field) is measured in tesla — weber per square metre.
Instrument → what it measures
very commonAn instrument name ending in -meter or -graph with its use asked: hygrometer, lactometer, anemometer, sphygmomanometer, seismograph.
How to solve: Read the Greek root: hygro (moisture), hydro (liquid), lacto (milk), anemo (wind), baro (air weight = pressure), seismo (quake), sphygmo (pulse). Then match the job to the root.
Example: Which instrument measures the relative humidity of air?
Hygrometer — 'hygro' means moisture. The hydrometer (and lactometer for milk) measures liquid density instead.
Everyday phenomenon → principle
very commonA daily-life effect — rocket, gun recoil, hydraulic brakes, floating ship, aeroplane lift, pressure cooker, sea breeze — and options listing laws/principles.
How to solve: Sort by story: resistance to a change of state → inertia (first law); force spread over more time → second law/momentum; push one way, move the other → third law; enclosed liquid force → Pascal; floating/upthrust → Archimedes; fast air, low pressure → Bernoulli; boiling/steam/cooling → latent heat, specific heat, evaporation.
Example: Hydraulic brakes work on the principle of:
Pascal's law — pressure applied to an enclosed liquid is transmitted equally in all directions, so a small pedal force becomes a large braking force.
Inventor / discoverer
very common'Who discovered the neutron?', 'who invented the television/telephone?', a match-the-column of scientists, devices and particles.
How to solve: Two tables to hold: particles (electron–Thomson, proton–Goldstein, neutron–Chadwick, nucleus–Rutherford, radioactivity–Becquerel, X-rays–Röntgen) and devices (Bell–telephone, Baird–TV, Marconi–radio, Edison–bulb, Faraday–dynamo, Watt–steam engine, Wright brothers–aeroplane).
Example: Who discovered the neutron?
James Chadwick (1932) — the neutral particle in the nucleus.
Eye defects and mirror/lens uses
very common'Myopia is corrected by…', 'which mirror is used as a rear-view mirror / in a torch?', 'which lens always forms a virtual diminished image?'
How to solve: Fix the pairs: myopia–concave, hypermetropia–convex, presbyopia–bifocal, astigmatism–cylindrical; concave mirror = shaving/dentist/headlight, convex mirror = rear-view; convex lens = magnifier/camera, concave lens = diverging, always virtual-erect-diminished.
Example: Myopia (short-sightedness) is corrected by using a:
Concave (diverging) lens — it pushes the image that forms in front of the retina back onto the retina.
Simple numericals (lens power, resistance, energy, temperature)
very commonA one-step calculation: power of a lens from focal length, two resistors in parallel, appliance watts into kWh, a temperature conversion, km/h to m/s.
How to solve: Memorise four one-liners: P = 1/f (f in metres, dioptre), 1/Rp = 1/R1 + 1/R2, units = W × h ÷ 1000, F = 9C/5 + 32 and km/h × 5/18 = m/s. Do the arithmetic in powers of ten to avoid slips.
Example: Two resistors of 6 Ω and 3 Ω are connected in parallel. What is their equivalent resistance?
1/R = 1/6 + 1/3 = 1/2, so R = 2 Ω — for two resistors, product over sum: (6 × 3)/(6 + 3) = 2 Ω.
Sound properties and uses
common'Sound cannot travel through…', 'bats navigate using…', audible range, which property gives pitch/loudness, echo and Doppler questions.
How to solve: Sound is longitudinal and needs a medium (fastest in solids, none in vacuum). Audible 20 Hz–20 kHz; below = infrasonic, above = ultrasonic (bats, SONAR, scans). Pitch ↔ frequency, loudness ↔ amplitude (dB).
Example: The pitch of a sound is determined by its:
Frequency — higher frequency sounds shriller. Amplitude decides loudness.