How does a microwave oven heat food?

A microwave oven uses microwave radiation (a type of electromagnetic wave) to heat food. The microwaves cause water molecules in food to vibrate rapidly, generating heat through friction. This heats food from inside out, unlike conventional ovens that heat from outside.

The sky appears blue due to Rayleigh scattering. When sunlight enters the atmosphere, gas molecules scatter shorter wavelengths (blue light) much more than longer wavelengths (red, orange). So when we look at the sky (away from the sun), we see mostly scattered blue light. At sunrise/sunset, light travels a longer path through atmosphere, scattering more blue light away, leaving red and orange.

Why do we see lightning before hearing thunder?

Light travels much faster (3 × 10⁸ m/s) than sound (343 m/s). Lightning and thunder occur simultaneously during a storm, but light reaches our eyes almost instantly while sound takes time to travel. You can estimate the distance of a storm by counting seconds between lightning and thunder — every 3 seconds ≈ 1 km.

What is sonar and how is it used?

SONAR (Sound Navigation And Ranging) uses ultrasound waves to detect objects underwater. A pulse of sound is emitted; the echo returns after bouncing off objects. Used by ships to measure ocean depth (echo sounding), detect submarines, and by fishermen to locate fish.

Everyday Science and Technology — TNPSC Group 4 Science Notes

Overview

Everyday science questions test whether students understand why familiar things work the way they do. TNPSC frequently asks about food science, household phenomena, medical technology, and practical applications of physics, chemistry, and biology. These are fun, logical questions that don't require deep formulas — just understanding.

Common Phenomena Explained

Light and Vision

Phenomenon	Explanation
Sky is blue	Rayleigh scattering — blue light (short wavelength) scattered most
Sunset is red/orange	Blue light scattered away; red/orange (long wavelength) reaches eyes
Rainbow	Dispersion of white sunlight through water droplets — VIBGYOR
Mirage	Total internal reflection of light in hot air layers near ground
Why objects have colour	Objects absorb some wavelengths; reflect others — reflected wavelength = colour seen

Sound

Phenomenon	Explanation
Thunder heard after lightning	Sound (343 m/s) much slower than light (3×10⁸ m/s)
Echo	Reflection of sound; minimum distance = 17.2 m
Why music sounds pleasant	Regular vibrations at harmonic frequencies
Noise cancellation	Opposite sound waves cancel each other out

Water and Temperature

Phenomenon	Explanation
Ice floats on water	Ice less dense (hexagonal crystal structure) than liquid water
Water boils at lower temperature on mountains	Lower atmospheric pressure = lower boiling point
Salt lowers freezing point of water	Solute disrupts water crystal formation — used to de-ice roads
Pressure cooker cooks faster	Higher pressure = higher boiling point (>100°C) = faster cooking
Sweating cools the body	Evaporation absorbs heat from skin

Household Science

Kitchen Chemistry

Item	Science Behind It
Baking soda (NaHCO₃)	Releases CO₂ when heated — makes cakes rise
Vinegar (acetic acid)	Acid — preserves food by preventing bacterial growth
Turmeric	Contains curcumin — natural antiseptic and anti-inflammatory; turns red with alkali (test for alkali)
Lemon juice (citric acid)	Prevents oxidation — stops fruit from browning
Salt as preservative	High salt concentration dehydrates bacteria (osmosis)
Copper vessels	Copper has antimicrobial properties — kills bacteria in water

Common Materials

Material	Key Property	Use
Teflon (PTFE)	Non-stick, high heat resistance	Non-stick cookware
Glass	Transparent, brittle, poor conductor	Windows, bottles
Rubber	Elastic, insulator	Tyres, gloves
Plastic	Lightweight, insulator, non-biodegradable	Packaging, containers
Fibreglass	Strong, lightweight	Boats, helmets
Carbon fibre	Very strong, very light	Aerospace, sports equipment

Medical Technology

Technology	Principle	Use
X-ray	X-ray radiation passes through soft tissue, blocked by bone	Bone fractures, chest imaging
Ultrasound (USG)	High-frequency sound waves reflect off organs	Foetal imaging, organ scans
MRI	Magnetic resonance of hydrogen atoms in body	Soft tissue imaging (brain, muscles)
CT Scan	Multiple X-rays from different angles	3D internal images
ECG (Electrocardiogram)	Records electrical activity of heart	Detecting heart conditions
EEG	Records electrical activity of brain	Detecting epilepsy, brain disorders
Endoscopy	Camera on flexible tube	Viewing internal organs directly
Dialysis	Artificial filtration of blood	Replaces kidney function

Communication Technology

Technology	How It Works
Mobile phone	Radio waves transmitted between phone and tower (GSM/LTE)
Wi-Fi	Radio waves (2.4 GHz or 5 GHz) carry data wirelessly
Bluetooth	Short-range radio waves (2.4 GHz)
GPS	Signals from 3+ satellites triangulate position
Optical Fibre	Light pulses travel through glass/plastic fibres (total internal reflection) — very high speed, no signal loss
Satellite TV	Signal sent from ground to geostationary satellite, reflected back to dish antenna
Internet (WWW)	Data transmitted through cables and wirelessly; invented by Tim Berners-Lee (1989)

Energy Sources

Renewable Energy

Source	How It Works	India's Status
Solar	Photovoltaic cells convert sunlight to electricity	India: 3rd largest solar capacity; Solar parks in Rajasthan, TN
Wind	Wind turbines generate electricity from wind kinetic energy	India: 4th largest wind power capacity; Tamil Nadu a top state
Hydroelectric	Flowing water turbines	Major dams: Bhakra-Nangal, Mettur (TN)
Biomass	Burning organic material or biogas	Rural energy; biogas from cattle waste
Tidal	Ocean tidal motion	Limited in India

Non-Renewable Energy

Source	Key Facts
Coal	~50% of India's electricity; largest reserves in Jharkhand, Odisha
Petroleum/Oil	Imported mainly; refined at refineries
Natural Gas	Cleaner fossil fuel; LNG imports
Nuclear	Uranium fission; Tarapur, Kudankulam (TN)

TNPSC Tip: Kudankulam Nuclear Power Plant is in Tamil Nadu (Tirunelveli district) — built with Russian collaboration.

Agriculture and Food Technology

Technology / Concept	Explanation
Green Revolution	1960s–70s; introduction of high-yield variety seeds, fertilizers, irrigation — M.S. Swaminathan in India
GM Crops	Genetically Modified — DNA altered to improve yield/pest resistance (e.g., Bt Cotton approved in India)
Organic Farming	No synthetic pesticides/fertilizers; sustainable
Drip Irrigation	Water delivered directly to roots — conserves water; promoted in Tamil Nadu
Pasteurisation	Heating milk to ~72°C briefly to kill pathogens — invented by Louis Pasteur
Refrigeration	Low temperature slows bacterial growth — preserves food

Science in Tamil Nadu Context

Topic	Tamil Nadu Connection
ISRO launch site	Satish Dhawan Space Centre, Sriharikota (Andhra Pradesh, near TN border)
Nuclear plant	Kudankulam Nuclear Power Plant, Tirunelveli
Wind energy	TN = leading state in wind power; Muppandal wind farm (Kanyakumari)
Solar energy	Sivaganga, Tirunelveli solar projects
Supercomputer	PARAM series developed by C-DAC
Defence	DRDO; missile testing at Wheeler Island (Odisha)
Medical science	AIIMS, JIPMER (Puducherry, near TN) for healthcare

Technology Abbreviations

Abbreviation	Full Form
ISRO	Indian Space Research Organisation
DRDO	Defence Research and Development Organisation
BARC	Bhabha Atomic Research Centre
TIFR	Tata Institute of Fundamental Research
CSIR	Council of Scientific and Industrial Research
ICAR	Indian Council of Agricultural Research
ICMR	Indian Council of Medical Research
DST	Department of Science and Technology
GPS	Global Positioning System
DNA	Deoxyribonucleic Acid
RNA	Ribonucleic Acid
LPG	Liquefied Petroleum Gas
CNG	Compressed Natural Gas
LED	Light Emitting Diode
LCD	Liquid Crystal Display

Previous Year TNPSC Questions (Pattern)

1. Q: Why does the sky appear blue? → Rayleigh scattering of blue light by atmosphere 2. Q: Which instrument is used for measuring blood pressure? → Sphygmomanometer 3. Q: Kudankulam Nuclear Power Plant is in which district? → Tirunelveli 4. Q: Pasteurisation is named after → Louis Pasteur 5. Q: Optical fibres work on the principle of → Total Internal Reflection 6. Q: The Green Revolution in India is associated with → M.S. Swaminathan 7. Q: Which gas is used in LPG cylinders? → Butane and Propane mixture 8. Q: SONAR uses → Ultrasound waves

Frequently Asked Questions

Ice floats on water because it is less dense than liquid water. When water freezes, its molecules arrange in a hexagonal lattice that takes up more space, making ice less dense (0.92 g/cm³) than liquid water (1.0 g/cm³). This unusual property of water is vital for aquatic life — ice insulates the water below in winter.