Science & Technology
Physics in Everyday Life
Physics in Everyday Life — Quick Revision
One-page CGPSC quick revision for Physics in Everyday Life: laws, values, units, devices and principles in tables for last-minute Prelims and Mains revision.
Motion and force, light and sound, and electricity and magnetism on one page. For explanations, go back to the chapter.
How to use this sheet
Scan it top to bottom in the week before Prelims. Bold entries are the facts examiners return to most often.
Key Values
| Quantity | Value |
|---|---|
| g on Earth | About 9.8 m/s²; Moon about one-sixth |
| Escape velocity (Earth) | About 11.2 km/s; independent of the object’s mass |
| Orbital velocity near Earth’s surface | About 7.9 km/s |
| Geostationary orbit | About 35,786 km above the equator; period = one rotation of Earth |
| Atmospheric pressure (sea level) | About \( 1.013 \times 10^{5} \) Pa |
| Speed of light (vacuum) | About \( 3 \times 10^{8} \) m/s; sunlight reaches Earth in about 8 min 20 s |
| Refractive index | Water about 1.33; glass about 1.5; diamond about 2.42 |
| Speed of sound in air | About 343 m/s at 20 °C (331 m/s at 0 °C); water about 1,500 m/s; steel about 5,000–6,000 m/s |
| Audible range | 20 Hz – 20 kHz |
| Minimum distance for an echo | About 17.2 m |
| Near point of a normal eye | About 25 cm |
| Persistence of vision | About 1/16 s |
| Household supply (India) | 230 V nominal (NCERT rounds to 220 V), 50 Hz AC |
| 1 kWh (“unit”) | \( 3.6 \times 10^{6} \) J |
| Tungsten melting point | About 3,400 °C |
SI Units
| Quantity | Unit |
|---|---|
| Force | newton (N) |
| Pressure | pascal (Pa) = N/m² |
| Momentum | kg m/s |
| Current | ampere (A) |
| Potential difference | volt (V) |
| Resistance | ohm (Ω) |
| Power | watt (W) |
| Energy | joule (J); commercial unit kWh |
| Frequency | hertz (Hz) |
| Lens power | dioptre (D) |
| Loudness | decibel (dB), a logarithmic scale |
Principle → Application
| Principle | Applications |
|---|---|
| Inertia (Newton’s 1st law) | Passengers lurch on braking or starting; seat belts; beating dust from a carpet |
| \( F = ma \), impulse | Airbags, catching with hands drawn back, sand in jump pits |
| Newton’s 3rd law / momentum conservation | Rocket, jet, gun recoil, walking, swimming |
| Centripetal force | Banking of roads, cyclist leaning on a turn; washing-machine dryer, cream separator |
| Pascal’s law | Hydraulic brakes, lift, jack, press |
| Archimedes’ principle | Ships, submarines, lactometer, hydrometer |
| Bernoulli’s principle | Aeroplane lift, roofs blown off in storms, sprayers |
| Refraction | Bent pencil, shallow-looking pond, twinkling stars, sunrise about 2 min early |
| Total internal reflection | Diamond sparkle, optical fibres, endoscopes, mirage |
| Dispersion | Prism spectrum (VIBGYOR), rainbow |
| Scattering | Blue sky, red sunset, red danger signals, white clouds, Tyndall effect |
| Concave mirror | Torches, headlights, shaving mirrors, solar cookers |
| Convex mirror | Rear-view mirrors |
| Ultrasound | Sonography, SONAR, crack detection, kidney stones, cleaning; bats |
| Doppler effect | Siren pitch change, speed guns, Doppler weather radar |
| Heating effect | Heater (nichrome), bulb (tungsten), fuse |
| Magnetic effect (Oersted, 1820) | Electromagnets, bells, cranes, MRI, maglev |
| Force on current in a magnetic field | Electric motor (Fleming’s left-hand rule) |
| Electromagnetic induction (Faraday, 1831) | Generator (Fleming’s right-hand rule), transformer, induction cooktop |
Eye Defects
| Defect | Cannot see | Lens |
|---|---|---|
| Myopia | Far objects | Concave |
| Hypermetropia | Near objects | Convex |
| Presbyopia | Near (age-related) | Bifocal / progressive |
| Astigmatism | Lines in some directions | Cylindrical |
| Cataract | Clouded lens | Surgery |
Noise Standards (Noise Pollution Rules, 2000), dB(A)
| Zone | Day | Night |
|---|---|---|
| Industrial | 75 | 70 |
| Commercial | 65 | 55 |
| Residential | 55 | 45 |
| Silence (100 m around hospitals, schools, courts) | 50 | 40 |
Household Electricity
| Item | Fact |
|---|---|
| Wiring | Parallel: full voltage to each appliance, independent switching |
| Fuse / MCB | In series in the live wire; against overloading and short circuits |
| Earthing | Against shock from appliances with metal bodies |
| RCCB / ELCB | Cuts supply on leakage current |
| Wire colours | Old: red live, black neutral, green earth. Current IS 732: brown, blue, green-yellow |
| Transmission | High voltage → low current → low \( I^{2}R \) loss |
| Transformer | AC only; step-up at power station, step-down near consumers |
| Korba | “Power capital” of Chhattisgarh (coal-based thermal power) |
Don’t Confuse
| This | vs | That |
|---|---|---|
| Mass: constant, kg | vs | Weight: \( mg \), varies, newton |
| g maximum at poles | vs | g minimum at equator (zero at Earth’s centre) |
| Escape velocity 11.2 km/s | vs | Orbital velocity about 7.9 km/s |
| Centripetal (real, inward) | vs | Centrifugal (pseudo, felt outward) |
| Refraction (twinkling) | vs | Total internal reflection (diamond, fibre, mirage) |
| Dispersion (rainbow) | vs | Scattering (blue sky) |
| Pitch: frequency | vs | Loudness: amplitude |
| Infrasound below 20 Hz | vs | Ultrasound above 20 kHz |
| Motor: left hand, electrical → mechanical | vs | Generator: right hand, mechanical → electrical |
| Fuse: protects circuit | vs | Earthing: protects people |
| Soft iron: electromagnet | vs | Steel: permanent magnet |
Favourite MCQ trap
“Astronauts in orbit are weightless because there is no gravity there.” Wrong. Gravity at orbital height is still strong. Astronauts feel weightless because they and their spacecraft are in continuous free fall around Earth.
Second favourite trap
“Danger signals are red because red light is scattered the most.” Reversed. Red is scattered the least by fog, dust and smoke, so it is visible from the greatest distance.
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