Key Fact
Applications
Radio: communication. Microwave: cooking, RADAR. IR: heat detection, remote control. Visible: vision. UV: sterilisation, vitamin D. X-ray: medical imaging. Gamma: cancer treatment.
-- NCERT Class 12 Physics, Ch. 8, p. 210Applications EM Waves
8 MCQs9-step worked example
Source: NCERT Electromagnetic WavesPYQ coverage: NEET 2022Official key: NTA-verifiedLast updated: 24 Sep 2026
Applications EM Waves, explained for NEET
A common confusion in this topic is not which band does a job, but why. Repeaters often rank the spectrum by energy and assume the most energetic band is the better tool for everything. It isn't. Every application NCERT lists is fixed by one thing: how that radiation interacts with the material it meets.
Five interaction mechanisms cover nearly every application in NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Resonant absorption. A microwave oven's frequency is matched to the resonant frequency of water molecules. Water sits throughout the food, absorbs that energy, and shares it as heat — so cooking is quick and not merely skin-deep.
Thermal emission and absorption. Hot bodies emit infrared. That single fact powers infrared lamps in physical therapy, infrared detectors on Earth satellites, remote switches, and the greenhouse warming of the atmosphere.
Selective damage. Ultraviolet is absorbed strongly by living cells, so UV lamps kill germs in water purifiers; the same absorption is why welders shield their eyes and why the ozone layer matters.
Penetration with contrast. X-rays cross soft tissue far more readily than bone, so a radiograph is a map of differential absorption — the same reason flaws inside metal castings can be found without cutting them open. Gamma rays penetrate further and ionise heavily, which makes them a treatment for malignant cells rather than a routine imaging tool.
Long-range propagation. Radio waves carry broadcast signals, and NCERT places cellular-phone voice transmission in the ultrahigh-frequency radio band — not in the microwave band.
In NEET this is usually a single mark: a straight match, or a one-step "why this band" question. Marks leak by swapping neighbours — radar is microwave, a TV remote is infrared, a water purifier is UV.
Watch-out: when a stem names a purpose, ask what the radiation must do to the material — be absorbed, pass through, or be re-emitted. Wavelength ranges, the E–B amplitude relation and displacement current belong to the other lessons of this unit.
Can you answer these Applications EM Waves MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
Radar systems used for aircraft navigation operate with which band of electromagnetic waves?
Show answer and why every option is right or wrong
Answer: C. Microwaves, because of their short wavelengths, are the band NCERT identifies as suitable for radar systems in aircraft navigation — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because radio waves are listed for broadcast and cellular communication, not for radar ranging; their wavelengths are far too long for the directional beams radar needs.
Why B is wrong: B is wrong because infrared is the band of heat waves emitted by hot bodies, used in therapy lamps, remote switches and satellite detectors — not in aircraft navigation.
Why D is wrong: D is wrong because ultraviolet is listed for its germicidal and tissue-damaging absorption (water purifiers, welding hazard), with no navigation application on page 210.
MCQ 2Easy RecallPractice
A domestic water purifier kills germs in the water using a lamp. Which band of electromagnetic radiation does that lamp emit?
Show answer and why every option is right or wrong
Answer: A. NCERT lists UV lamps as the means of killing germs in water purifiers, because ultraviolet is strongly absorbed by living cells — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why B is wrong: B is wrong because infrared deposits heat in the water rather than being selectively absorbed by micro-organisms; its listed uses are heating and detection, not sterilisation.
Why C is wrong: C is wrong because microwave energy is absorbed by the water molecules themselves, which heats the whole sample — that is the oven mechanism, not a germicidal one.
Why D is wrong: D is wrong because radio waves pass through water with negligible biological absorption, which is why they are used for communication rather than sterilisation.
MCQ 3Easy RecallPractice
According to NCERT, cellular phones transmit voice communication using which band, in its ultrahigh-frequency region?
Show answer and why every option is right or wrong
Answer: D. NCERT states that cellular phones use radio waves in the ultrahigh-frequency (UHF) band to transmit voice communication — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because infrared is short-range and blocked by walls and bodies; its communication use is the line-of-sight remote switch, not mobile telephony.
Why B is wrong: B is wrong because the microwave applications named on page 210 are radar and the microwave oven; NCERT places cellular voice transmission in the UHF radio band, and this swap is the usual loss on this question.
Why C is wrong: C is wrong because gamma rays are ionising radiation used in nuclear medicine and the destruction of malignant cells — they carry no communication application.
MCQ 4Direct ApplicationPractice
A microwave oven is built so that its frequency matches the resonant frequency of water molecules. This design makes the food cook rapidly and throughout its volume because
Show answer and why every option is right or wrong
Answer: B. The resonance match means the water present all through the food absorbs the energy directly, and that energy is then shared as heat — so the heating is volumetric rather than surface-inward — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because it reverses the energy order — microwaves are less energetic per photon than infrared — and in any case the mechanism here is resonant absorption by water, not raw photon energy.
Why C is wrong: C is wrong because surface reflection would give exactly the slow, skin-deep heating that the oven avoids; the point of the resonance match is absorption inside the food.
Why D is wrong: D is wrong because ionisation is the mechanism of X-rays and gamma rays; microwave energy sets water molecules into resonant motion, which appears as heat, with no ionisation involved.
MCQ 5Direct ApplicationPractice
A rescue team must locate a trapped person under debris in complete darkness, with no light source available. Which band should the detector be built for, and on what basis?
Show answer and why every option is right or wrong
Answer: A. NCERT identifies infrared as the radiation produced by hot bodies, which is why infrared detectors work on emitted radiation and need no source of their own — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why B is wrong: B is wrong because it still requires an external UV source, and NCERT's ultraviolet applications are germicidal and damaging absorption in living cells, not imaging.
Why C is wrong: C is wrong because the microwave applications listed are radar ranging and oven heating; nothing on page 210 supports body-versus-rubble reflection contrast, and the method would still need an emitter.
Why D is wrong: D is wrong because gamma rays would have to be supplied by a source and would ionise the very person being rescued; their listed use is destroying malignant cells, not locating living ones.
MCQ 6Direct ApplicationPractice
A welder is required to wear goggles fitted with special glass while striking an arc. The physical reason is that
Show answer and why every option is right or wrong
Answer: D. NCERT states that welders wear special glass goggles or face masks because welding arcs produce a large amount of ultraviolet, which is strongly absorbed by — and damaging to — the tissues of the eye — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because microwaves are not an arc emission of concern here; their heating action is on water and is the oven application, not an eye hazard requiring goggles.
Why B is wrong: B is wrong because radio waves pass through tissue with negligible absorption, which is precisely why they are used for communication rather than being a shielding problem.
Why C is wrong: C is wrong because an electric arc is a thermal and atomic-excitation source; gamma rays come from nuclear processes and are not produced by welding.
MCQ 7Concept TrapPractice
On a medical radiograph, bone appears clearly distinguished from the surrounding soft tissue. The property of X-rays that makes this possible is that
Show answer and why every option is right or wrong
Answer: B. X-rays are a diagnostic tool precisely because their absorption differs between bone and soft tissue; the radiograph is a map of that differential absorption, and NCERT also cautions that overdoses are harmful — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because the image is formed by radiation transmitted through the body onto the plate, not by radiation reflected back from bone.
Why C is wrong: C is wrong because bone does not become an X-ray source; the beam originates in the X-ray tube and what varies is how much of it each tissue absorbs.
Why D is wrong: D is wrong because it invents a conversion inside the bone; any conversion to visible light happens in the detecting screen or film, not in the patient.
MCQ 8Concept TrapPractice
A student argues that because gamma rays are the most penetrating electromagnetic radiation, they would be the best choice for routine dental imaging. The flaw in this argument is that
Show answer and why every option is right or wrong
Answer: C. Imaging needs contrast, not maximum penetration; NCERT assigns gamma rays to nuclear medicine and the destruction of malignant cells, and X-rays to diagnosis, exactly because of how each is absorbed — NCERT Class 12 Physics, Chapter 8 (Electromagnetic Waves), page 210.
Why A is wrong: A is wrong because availability is not the physics objection — gamma sources are used clinically in treatment; the objection is contrast and dose.
Why B is wrong: B is wrong because it overstates the case: gamma rays are absorbed, just too weakly and too indiscriminately by soft tissue and bone to produce a useful difference on the plate.
Why D is wrong: D is wrong because it reverses the ordering — gamma rays lie beyond X-rays at the short-wavelength end — and resolution is not what disqualifies them here.
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How do you solve a Applications EM Waves question? A worked example
- 1
Given.
A hospital committee lists three jobs: (i) image a suspected fracture in a patient's wrist, (ii) sterilise the drinking-water supply on a ward, (iii) destroy a deep-seated malignant tumour. The available bands are radio, microwave, infrared, visible, ultraviolet, X-ray and gamma.
- 2
Required.
One band for each job, together with the interaction mechanism that justifies the choice.
- 3
Concept.
An application is fixed by what the radiation must do to the material — be absorbed selectively, pass through with contrast, or deposit energy. It is not fixed by which band sits highest on an energy ladder (NCERT Class 12 Physics, Chapter 8, page 210).
- 4
Formula used.
None. This is a selection by interaction mechanism, not a numerical relation; the wave-speed and E–B amplitude relations belong to the characteristics lesson, not to this one.
- 5
Substitution.
Match each job to the mechanism it demands:• (i) needs a beam that crosses the body but is absorbed differently by bone and soft tissue → differential absorption.• (ii) needs energy absorbed strongly by living cells while the water itself stays usable → selective germicidal absorption.• (iii) needs energy delivered deep inside tissue with enough ionising effect to destroy cells → deep penetration plus ionisation.
- 6
Calculation (reasoning chain).
Infrared and microwaves only deposit heat, giving no image and no depth control — eliminate for (i) and (iii). Visible light cannot cross tissue — eliminate for (i). Radio passes through with almost no absorption contrast — eliminate for (i). That leaves X-rays for (i). For (ii), UV is the band NCERT names for water purifiers. For (iii), X-rays are a diagnostic tool at imaging doses, while gamma rays are the band NCERT assigns to destroying malignant cells. No numerical constant enters this example, so no significant-figure accounting applies.
- 7
Final answer.
(i) X-rays, (ii) ultraviolet, (iii) gamma rays.
- 8
Common trap.
Ranking bands by penetrating power and then picking the most penetrating for every job. Diagnosis needs contrast, not maximum penetration — and a band chosen for heating (infrared, microwave) cannot image at all.
- 9
Similar NEET-style question.
Faults and cavities inside a thick metal casting must be located without cutting it open. Which band is used, and what property makes it work? *(Answer: X-rays — they penetrate the casting, but a cavity absorbs less than solid metal, so the flaw shows up as a contrast on the plate.)*
What to remember before solving Applications EM Waves questions
More in Electromagnetic Waves: 2 exam traps and mistakes · 4 formulas · 3 question patterns from its other lessons.
Applications EM Waves questions from past NEET papers
1 question from NEET 2022. Answers verified against NTA official keys. — click to collapse
NEET 2022
The energy that will be ideally radiated by a 100 kW transmitter in 1 hour is
11 × 10⁵ J
236 × 10⁷ J
336 × 10⁴ J
436 × 10⁵ J
NTA Answer: Option 2(final)
Sources
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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