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UPPCS Physics Gap Sheet: Electromagnetic Waves and Applications.
UPPCS has asked 23 of these. 6 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
Electromagnetic waves need no material medium. All travel at the same speed in vacuum, but differ in frequency and wavelength. From radio waves towards gamma rays, frequency and photon energy increase.
A device uses the part of the spectrum suited to its task. Infrared detects warmth, microwaves support radar and satellite links, and X-rays image internal structures. Gravitational waves and cosmic-ray particles belong to different categories.
✅ Already asked (23)
Spectrum
- Radio waves · They have the longest wavelengths in the electromagnetic spectrum.
- Microwaves · Used in satellite links, radar and microwave ovens.
- Infrared · Often associated with thermal radiation; invisible to the unaided human eye.
- Visible spectrum · Its approximate range is 380–780 nanometres; boundaries are not sharp.
- Ultraviolet · Has shorter wavelengths than visible violet; it can cause skin and eye damage.
- X-rays · Penetrating electromagnetic radiation used in medical imaging.
- Vacuum speed · All electromagnetic waves travel at about 300,000 kilometres per second in vacuum.
Communication and sensing
- Ordinary TV remote · Typically sends infrared signals; some modern remotes use radio links.
- RADAR · Uses reflected radio waves, often microwaves, to detect range and motion.
- Optical-fibre communication · Carries information in light pulses guided through the fibre.
- Satellite rain fade · Rain can absorb and scatter microwave signals.
- Thermal camera · Detects infrared radiation emitted by objects.
- Terrestrial TV range · Earth's curvature limits line-of-sight broadcasting; relay stations extend coverage.
- Frequency modulation · FM varies a carrier's frequency to encode information.
Imaging and other waves
- CT scan · Uses X-rays from multiple directions to reconstruct internal cross-sections.
- MRI · Uses magnetic fields and radio-frequency pulses, not X-rays.
- Hard X-rays · Higher-energy X-rays generally penetrate more deeply than soft X-rays.
- Cosmic rays · Primary cosmic rays are mainly high-energy protons and atomic nuclei.
- Gravitational waves · Ripples in spacetime; the first direct detection was on 14 September 2015.
- Polarisation · Shows that light is transverse; polarising filters can reduce reflected glare.
Further spectrum applications
- Phosphorescence · Light emission continues after excitation stops, giving an afterglow.
- Redshift · Spectral lines shift to longer wavelengths; recession or cosmic expansion can cause it.
- Ionospheric reflection · Some radio frequencies return from the ionosphere, enabling communication beyond the horizon.
❌ Not asked yet (6)
Items marked 'asked in other exams' have come in UPSC or other state exams, not yet in UPPCS.
🔒 6 items not asked yet
Spectrum: 1 · Further spectrum applications: 5
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⚠️ CT uses X-rays; MRI uses strong magnetic fields and radio-frequency pulses. Cosmic rays are mainly energetic particles, not an electromagnetic band.
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