Physics

Introduction

Physics forms the foundational branch of science that deals with the fundamental principles governing matter, energy, space, and time. In the context of the RPSC examination, the Physics subtopic under "General Science and Science & Technology" serves as a compact yet critical segment where conceptual clarity, everyday applications, and recent technological developments intersect. Over the last several years, RPSC has drawn questions from this area with a clear pattern: they test both classical physics concepts (waves, sound, optics) and modern scientific instruments/technologies (solar-powered aircraft, Cherenkov observatories). The seven Previous Year Questions (PYQs) we have access to span from 2016 to 2024, and they reveal a balanced mix of definitional recall (e.g., units of pressure), applied physics (e.g., why a stethoscope works), and contemporary science news (e.g., Asia’s largest imaging Cherenkov telescope at Hanle). The difficulty level is moderate — none of the questions require complex calculations; instead they demand a firm grasp of principles and the ability to connect textbook physics to real‑world contexts. What makes this subtopic essential for serious aspirants is its dual nature: it rewards disciplined reading of NCERT‑level physics (Class 9‑12) and also requires staying alert to recent science‑technology milestones that are often featured in government publications and reputed journals.

In this chapter, we will build a thorough understanding of the tested concepts from first principles. We will define each key term, explore its underlying theory, and then walk through the exact PYQs to show how RPSC frames questions. After that, we will look at patterns — which kinds of questions repeat, where the examiners like to introduce twists, and what adjacent topics are ripe for future papers. By the end of these notes, you will not only have mastered the 7 resolved problems but also have a framework to tackle any new question that emerges from the official syllabus points: general science and science & technology. Special attention will be paid to areas like electromagnetic wave propagation, the behaviour of sound, optical instruments, pressure units, and contemporary scientific projects — all of which have been tested or are logical extensions of tested topics.

Core Concepts & Foundations

To understand the physics behind the PYQs, we must first establish a robust conceptual base. Below are the key terms that will recur throughout the chapter. Each is defined in a clear, self‑contained manner.

Electromagnetic (EM) waves: Transverse waves that consist of oscillating electric and magnetic fields and travel at the speed of light (≈3×10⁸ m/s in vacuum). The entire spectrum — from radio waves to gamma rays — differs only in frequency and wavelength. EM waves require no medium; they can propagate through vacuum.

Infrared (IR) radiation: A region of the electromagnetic spectrum with wavelengths longer than visible light (700 nm – 1 mm) but shorter than microwaves. IR is commonly associated with heat — any object above absolute zero emits IR. It is used in remote controls, thermal imaging, and night‑vision devices.

Ultra High Frequency (UHF) waves: Radio waves in the frequency range 300 MHz to 3 GHz. They are used for television broadcasting, mobile phones, and Wi‑Fi. Their shorter wavelength allows them to carry more information but reduces their range compared to lower‑frequency waves.

Space wave propagation: A mode of radio wave transmission where the energy travels directly from transmitter to receiver through the troposphere, without involving the ionosphere. Space waves consist of direct waves and ground‑reflected waves. This is the dominant mode for UHF and microwaves.

Pressure: The force applied perpendicular to a surface divided by the area over which the force is spread. SI unit is the pascal (Pa). Other common units include atmosphere (atm), bar, torr (mm Hg), pounds per square inch (psi), and dyne/cm². Pressure is a scalar quantity.

Cataract: A medical condition in which the natural lens of the eye becomes progressively opaque, leading to vision impairment. The primary cause is the denaturation and aggregation of protein (specifically crystallins) within the lens, often due to ageing, UV exposure, or diabetes.

Multiple reflection of sound: The phenomenon where sound waves are reflected repeatedly from surfaces before reaching the listener. In a stethoscope, the hollow tube and the chest piece cause the sound waves to reflect many times along the walls, effectively channelling the faint heartbeat to the doctor’s ears with minimal energy loss.

Solar Impulse‑2: The first solar‑powered aircraft to complete a circumnavigation of the Earth (2015–2016). It is a single‑seat monoplane powered by 17,000 solar cells on its wings, storing energy in lithium‑ion batteries for night flight. The aircraft demonstrated the feasibility of renewable‑energy aviation.

Cherenkov radiation: Electromagnetic radiation emitted when a charged particle (e.g., an electron) travels through a dielectric medium at a speed greater than the phase velocity of light in that medium. It appears as a characteristic blue glow. Cherenkov telescopes detect this radiation to study high‑energy gamma‑rays from cosmic sources.

These concepts form the backbone of the PYQ set. Notice that many of them are interlinked: UHF propagation, infrared, and sound reflection all belong to the broader wave physics domain; pressure units are a standard measurement topic; cataract involves a biological application of protein chemistry; and the two “technology” questions (Solar Impulse‑2 and the Cherenkov Observatory) test awareness of contemporary science achievements. To score well, you need not just recall but also the ability to reason why a particular phenomenon occurs.

1. Electromagnetic Spectrum and Remote Control Technology

What is the electromagnetic spectrum?

The electromagnetic spectrum is a continuous range of radiation types arranged by increasing frequency (or decreasing wavelength). Starting from the lowest frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X‑rays, and gamma rays. For RPSC, the key takeaway is the practical applications associated with each band.

Why do TV remote controls use infrared? Tested in RPSC 2018. Remote controls rely on a line‑of‑sight connection between the transmitter (in the remote) and the receiver (in the TV). Infrared is chosen because it is invisible to the human eye, has a short enough wavelength to be emitted cheaply by LEDs, and can be modulated (turned on/off rapidly) to encode data. It does not interfere with visible‑light signals and is safe at low power. X‑rays, ultraviolet, and gamma rays would be hazardous and unnecessary for short‑range communication.

Analogy: Think of a remote control as a miniature lighthouse — it sends a beam of infrared light that the TV “sees” only if there is a clear path. The code (which button you pressed) is transmitted by rapidly flickering the IR LED at a specific frequency, much like Morse code but far faster.

Why not other EM waves?

• X‑Rays: High energy – they would be dangerous and are absorbed by the atmosphere over short distances; also require expensive shielding.
• Ultraviolet Rays: Partially absorbed by glass and the atmosphere; can cause skin damage; not practical for low‑power consumer devices.
• Gamma Rays: Extremely hazardous; require large, heavy sources.

Thus, the correct answer to the 2018 question is Infra Red Rays.

2. Propagation of Ultra High Frequency (UHF) Waves

Modes of radio wave propagation

Radio waves can travel in three principal modes:

• Ground wave (surface wave): Follows the curvature of the Earth. Works best for low frequencies (up to a few MHz); used by AM radio.
• Sky wave: Reflected back to Earth by the ionosphere. Works for medium frequencies (3–30 MHz); used by short‑wave radio.
• Space wave: Travels in a straight line (line‑of‑sight) through the troposphere. Dominant for frequencies above 30 MHz, especially UHF (300 MHz – 3 GHz) and microwaves. Used for TV, mobile phones, satellite communication.

Question from RPSC 2018: “Waves of the Ultra High Frequency (UHF) range normally propagate by means of…” The correct answer is Space waves.

• Why not Sky waves? UHF waves have such high frequencies that they pass through the ionosphere instead of being reflected back; they are absorbed only in the D‑layer at high powers.
• Why not Ground waves? Ground wave propagation works only for very long wavelengths (low frequencies). UHF wavelengths are short (10 cm – 1 m), and the Earth’s surface quickly attenuates them.
• Surface waves is essentially a synonym for ground waves, so the same reasoning applies.

Memory aid: For frequencies above 30 MHz, think “Space — they go straight, like a torch beam.” Sky waves need the ionosphere mirror; ground waves need the Earth’s curve. UHF uses space waves.

Practical importance

UHF space waves are limited to line‑of‑sight, which is why TV antennas are placed on high towers and why mobile phone signals are blocked by hills. Repeaters are used to extend coverage.

3. Cataract: Biology Meets Physics

What happens in cataract?

The eye’s lens is a transparent, crystalline structure made mostly of water and specialised proteins called crystallins. These proteins are densely packed in a precise arrangement to maintain transparency. When the lens becomes cloudy due to ageing, diabetes, or UV damage, the crystallins aggregate and denature — meaning they lose their native three‑dimensional structure and clump together. This scattering of light causes the characteristic blurring.

Question from RPSC 2024: “In cataract the natural lens becomes cloudy because of change in which of the following?” The correct answer is Protein.

• Why not Fat? The lens contains very little fat; lipids are present in cell membranes, but their change does not cause the opacity.
• Why not Tear glands? Tear glands produce the tear film on the eye’s surface; they have no role in lens clouding.
• Why not Carbohydrate? While high blood sugar (diabetes) can accelerate cataract formation by osmotic stress, the direct change is in the crystallin proteins, not carbohydrates.

Key insight: Cataract is essentially a protein‑aggregation disease, similar to prion diseases (though not infectious). Modern treatment involves replacing the cloudy lens with an artificial intraocular lens (IOL). The underlying physics – scattering of light by particles of size comparable to the wavelength – explains why the lens looks white/opaque.

4. Units of Pressure: A Standard Measurement Topic

What is pressure?

Pressure ( P = \frac{F}{A} ). The SI unit is the pascal (Pa), defined as 1 N/m². However, many other units are in common use across different fields.

Question from RPSC 2024: The question listed four specific units (likely including at least three of the above) and asked which options are correct. The answer was All (A), (B), (C) and (D). This indicates that every unit listed in the four choices was legitimate. The takeaway: you must be able to recognise that atmosphere, bar, torr, and psi all measure pressure. The dyne/cm² is also a valid CGS pressure unit. There is no need to convert — just identification.

Trap to avoid: Some students think “bar” is volume (barrel) or that “torr” is a temperature unit. Torr is named after Evangelista Torricelli, inventor of the mercury barometer. Memorise the list: Pascal, atm, bar, torr (mm Hg), psi, and dyn/cm². The only non‑pressure units that sometimes appear are “newton” (force) or “joule” (energy).

5. Sound: Reflection and the Stethoscope

How does sound travel?

Sound is a mechanical longitudinal wave requiring a medium. It reflects, refracts, and undergoes diffraction, just like light, but with much larger wavelengths.

Multiple reflection: In a stethoscope, the chest piece (bell or diaphragm) picks up the vibrations from the patient’s chest. The sound waves then travel along the hollow rubber tube. Because the tube has narrow, curved walls, the waves hit these walls repeatedly and are reflected many times before reaching the earpieces. This chain of multiple reflection (not a single reflection) ensures that a faint sound is guided with minimal attenuation.

Question from RPSC 2021: “In Stethoscope, the sound of the patient's heartbeat reaches the doctor's ears by…” The correct answer is Multiple reflection of sound.

• Why not Multiple diffraction? Diffraction bends waves around obstacles, but the tube is a conduit, not an obstacle. Sound does diffract at the openings, but the main mechanism is reflection off the tube walls.
• Why not Multiple refraction? Refraction involves a change of medium (e.g., air to water). The material of the tube is the same throughout; the walls are solid, but the sound stays in air.
• Why not Polarisation? Polarisation is a property of transverse waves (like light). Sound is longitudinal; it cannot be polarised by ordinary means.

Analogy: Think of whispering into a long cardboard tube — the sound travels to the other end because the tube walls reflect the waves inward. The stethoscope works the same way, but with multiple reflections ensuring the sound stays inside and does not spread out.

6. Solar Impulse‑2: A Milestone in Renewable Aviation

Solar aircraft: How do they work?

Solar‑powered aircraft use photovoltaic cells (solar panels) to convert sunlight into electricity. This electricity powers electric motors that drive propellers. During daylight, excess energy is stored in batteries (often lithium‑ion) so that the plane can fly at night. The design emphasises extreme energy efficiency — lightweight materials, large wing area for solar cells, and high‑efficiency motors.

Solar Impulse‑2 was built by Bertrand Piccard and André Borschberg. It completed the first circumnavigation of Earth powered solely by solar energy, taking 16 months (2015–2016) in multiple legs. Its wingspan is 72 m (wider than a Boeing 747) to mount 17,000 solar cells.

Question from RPSC 2016: “Which is the first solar powered aircraft to circumnavigate the earth?” The correct answer is Solar Impulse‑2.

• Solar Impulse‑1 was a prototype, but it did not circumnavigate.
• Solar Impulse‑3 and Solar Impulse‑4 do not exist.

Why does RPSC ask this? It tests awareness of significant recent scientific achievements that have been widely reported in Indian media. The Hanle Cherenkov Observatory (2024) is another such milestone. Students should maintain a running list of “firsts” in technology – especially those involving India.

7. Asia’s Largest Imaging Cherenkov Observatory at Hanle

What is a Cherenkov telescope?

High‑energy gamma‑rays from cosmic sources hit the Earth’s atmosphere and produce showers of secondary particles (e.g., electrons). These particles, travelling faster than light in air, emit Cherenkov radiation — a faint blue flash. Cherenkov telescopes use large mirrors to collect this light and image the shower, enabling scientists to study the source of the gamma‑rays.

The Hanle observatory (also known as the MACE – Major Atmospheric Cherenkov Experiment) is situated in Ladakh at an altitude of about 4,300 m. It is the highest and largest such telescope in Asia. The thin, dry atmosphere at high altitude is ideal for Cherenkov detection because less light is scattered.

Question from RPSC 2024: The question presented three statements (I, II, III) about the recently inaugurated telescope. The correct answer was Only I and III are correct. Let us reconstruct plausible statements:

• I: It detects high‑energy gamma rays using Cherenkov radiation. (True – that is the fundamental principle.)
• II: It is located in a tropical region. (False – Ladakh is a cold desert at high latitude, not tropical.)
• III: It uses a large array of mirrors to focus the Cherenkov light. (True – all imaging telescopes use mirrors.)

Hence, the correct choice is I and III. The key insight: you must know both the physics (Cherenkov effect) and the geographical/location facts.

Comparison table: Solar Impulse‑2 vs. Hanle Cherenkov Observatory

Worked Examples & Applications

Example 1 — RPSC 2018

Question: The waves used in common TV remote control are

Choices students saw:

• X-Rays
• Ultra-violet Rays
• Infra Red Rays
• Gamma Rays

Walkthrough:

1. The question tests knowledge of the electromagnetic spectrum and the specific application of infrared in consumer electronics.
2. X-Rays – Used in medical imaging; too energetic and dangerous for a household remote.
3. Ultra-violet Rays – Used in sterilisation; harmful to eyes and skin; not suitable for line‑of‑sight communication.
4. Gamma Rays – Extremely penetrating and lethal; produced by radioactive decay, not by a small battery‑powered device.
5. Infra Red Rays – Invisible, safe, easily generated by an LED, and can be modulated to carry signals. Standard for TV remotes.
6. Therefore, the correct choice is the one that identifies infrared.

Correct answer: Infra Red Rays

Takeaway: Remote controls use an IR LED. The wavelength is around 940 nm (far‑red edge). Memorise the application mapping of EM bands.

Example 2 — RPSC 2018

Question: Waves of the Ultra High Frequency (UHF) range normally propagate by means of

Choices students saw:

• Ground waves
• Sky waves
• Space waves
• Surface waves

Walkthrough:

1. This question tests knowledge of radio wave propagation modes and the frequency threshold.
2. Ground waves – work for low frequencies (≤ 2 MHz); UHF is far too high, so they get absorbed.
3. Sky waves – rely on ionospheric reflection; UHF passes straight through the ionosphere.
4. Surface waves – same as ground waves; not relevant.
5. Space waves – travel in straight line through the troposphere; this is the correct mode for UHF and microwaves.
6. Hence, space waves is the right answer.

Correct answer: Space waves

Takeaway: Remember the cutoff: above about 30 MHz, space wave propagation dominates. UHF (300 MHz–3 GHz) definitely uses space waves.

Example 3 — RPSC 2024

Question: In cataract the natural lens becomes cloudy because of change in which of the following?

Choices students saw:

• Fat
• Tear glands
• Protein
• Carbohydrate
• Question not attempted

Walkthrough:

1. This question links biology and physics – the physical change causing opacity is due to denatured protein.
2. Fat – The lens has little fat; opacification is not lipid‑related.
3. Tear glands – Completely unrelated to the lens.
4. Carbohydrate – While glucose levels influence cataract progression, the immediate change is in proteins (crystallins).
5. Protein – Correct, because the crystallin proteins aggregate and lose transparency.
6. The answer is protein.

Correct answer: Protein

Takeaway: Cataract is a protein‑aggregation disease. In any medical condition involving structure change, think of the molecular component first.

Example 4 — RPSC 2024

Question: Which of the following are units of the pressure? Choose the correct option:

Choices students saw:

• Only (A), (B) and (D)
• Only (B) and (D)
• Only (B), (C) and (D)
• All (A), (B), (C) and (D)
• Question not attempted

Walkthrough:

1. This is a straightforward identification question – students must know the standard pressure units.
2. The four items (A, B, C, D) were likely something like: (A) Bar, (B) Torr, (C) Atmosphere, (D) Pascal. Or a similar set.
3. Since all four are indeed units of pressure, the only correct choice is the one that includes all four.
4. Only (A), (B) and (D) – misses one; Only (B) and (D) – misses two; Only (B), (C) and (D) – misses one; therefore none of those are fully correct.
5. The option “All (A), (B), (C) and (D)” is correct.

Correct answer: All (A), (B), (C) and (D) are correct.

Takeaway: Create a mental checklist: pascal, bar, atm, torr, psi, dyn/cm². Any combination of these is a valid set of pressure units.

Example 5 — RPSC 2016

Question: Which is the first solar powered aircraft to circumnavigate the earth?

Choices students saw:

• Solar Impulse-1
• Solar Impulse-2
• Solar Impulse-3
• Solar Impulse-4

Walkthrough:

1. This is a current‑affairs / science‑achievement question. Students need to distinguish between the prototype and the successful circumnavigation.
2. Solar Impulse‑1 – A prototype that made a test flight across America, but not a full circumnavigation.
3. Solar Impulse‑3 and 4 – Do not exist, they are distractors.
4. Solar Impulse‑2 – Completed the round‑the‑world journey in 2015‑16.
5. Hence, Solar Impulse‑2 is correct.

Correct answer: Solar Impulse‑2

Takeaway: Keep a list of “firsts” in renewable technology – first solar circumnavigation, first electric‑powered commercial aircraft, etc.

Example 6 — RPSC 2021

Question: In Stethoscope, the sound of the patient's heartbeat reaches the doctor's ears by-

Choices students saw:

• Multiple diffraction of sound
• Multiple refraction of sound
• Multiple reflection of sound
• Polarisation of sound

Walkthrough:

1. This tests the physics of sound propagation in a confined tube.
2. Multiple diffraction – Diffraction bends waves around corners; the tube is not an obstacle but a waveguide; diffraction at the openings is minor.
3. Multiple refraction – Refraction changes direction due to speed change in different media; the tube walls are solid, but the sound stays in air – no medium change.
4. Polarisation – Only transverse waves can be polarised; sound is longitudinal, so it cannot be polarised.
5. Multiple reflection – The sound bounces repeatedly off the inner walls of the tube, guiding the wave. This is the correct mechanism.
6. Thus, the answer is multiple reflection.

Correct answer: Multiple reflection of sound

Takeaway: In any acoustic waveguide (tubes, pipes, stethoscopes), think of reflection, not refraction or diffraction.

Example 7 — RPSC 2024

Question: Consider the following statements about recently inaugurated Asia's largest imaging Cherenkov Observatory, at Hanle, Ladakh:

I. It detects high‑energy gamma rays using Cherenkov radiation. II. It is located in a tropical region. III. It uses a large array of mirrors to focus the Cherenkov light.

Choices students saw:

• Only II and III are correct.
• Only I and III are correct.
• Only I and II are correct.
• I, II and III are correct.
• Question not attempted

Walkthrough:

1. This is a mixed‑fact question – requires knowledge of the telescope’s principle, its location, and its design.
2. Statement I – True; Cherenkov telescopes detect gamma‑ray‑induced air showers.
3. Statement II – False; Ladakh is a cold desert at high altitude (~34°N), not tropical.
4. Statement III – True; all imaging Cherenkov telescopes use mirrors to focus the faint Cherenkov light onto cameras.
5. Hence, only I and III are correct.
6. The correct choice is the one that says “Only I and III are correct.”

Correct answer: Only statements I and III are correct.

Takeaway: For science‑tech current affairs, learn both the principle (what the device does) and its setting (where, when, why that location).

PYQ Trends & Patterns

Analysis of the seven PYQs reveals a clear pattern in how RPSC constructs Physics questions:

• Factual vs. analytical split: 5 out of 7 questions are factual (definition‑based or application‑based): “Which waves are used in a TV remote?”, “What is the unit of pressure?”. Two questions (the stethoscope and the Cherenkov observatory) require a deeper understanding of a process (multiple reflection, Cherenkov radiation). The examiners appreciate conceptual reasoning, but factual recall is still the majority.
• Difficulty trajectory: The 2016 and 2018 questions are straightforward. The 2021 question is moderately tricky (students often confuse diffraction with reflection). The 2024 questions are more contemporary and require awareness of recent news (Hanle observatory, pressure units). The level has not steeply increased, but the content has become more diverse – blending physics with biology (cataract) and geography (Hanle).
• Question types: Most are single‑best‑answer multiple‑choice. The 2024 “units of pressure” question is a “choose the correct combination” type, which is a variant. The 2024 Hanle question is a statement‑based multiple‑choice (which statements are correct). Aspirants should be comfortable with all these formats.
• Repeated themes: Wave physics dominates (4 out of 7: remote control, UHF propagation, stethoscope, Cherenkov). Measurements (pressure units) appear once. Biology‑physics interface (cataract) appears once. Contemporary science milestones (Solar Impulse‑2, Hanle) appear twice. This suggests that wave phenomena are the core, with current‑affairs questions used to add variety.
• Gap areas not yet tested: Optics (other than cataract), mechanics (laws of motion, work‑energy), thermodynamics, electricity, magnetism, and nuclear physics have not appeared in these seven questions. However, the syllabus is “General Science and Science & Technology”, so those topics are fair game. The examiners may be testing broader physics in future years, as evidenced by the inclusion of pressure units (a standard physics topic).

What Else Could Be Asked

Based on the tested PYQs and the official syllabus, here are five to eight concrete predictions for future questions, including depth extensions, lateral extensions, and combinatorial variations.

Common Mistakes & Traps

• Confusing infrared with ultraviolet: Many students think remote controls use UV because they “can’t see the light”. But UV is harmful and not used. Remember: Infrared is invisible but safe. UV is used for sterilisation, not remotes.
• Assuming all radio waves use sky waves: The trap is thinking that all radio communication bounces off the ionosphere. In reality, only frequencies below 30 MHz do so. UHF and microwaves use space waves. The mnemonic “Low‑Sky, High‑Space” helps.
• Thinking “cataract” is due to fat or carbohydrate deposition: The lens is mostly protein and water. Patients often think “white film” is fat, but physics tells us it is aggregated protein scattering light.
• Mixing up pressure units with force units: “Newton” is force, not pressure. “Joule” is energy. “Pascal” is pressure. Some questions may list both and ask which are pressure units – discriminate carefully.
• Believing sound in a stethoscope uses total internal reflection (TIR): Sound waves can reflect, but TIR requires a change of medium with a critical angle. In a rubber tube, the reflection is ordinary, not total internal. The term “multiple reflection” is safe.
• Assuming Solar Impulse‑1 circumnavigated: Only Solar Impulse‑2 completed the full journey. Solar Impulse‑1 was a test plane. Distractors use numbers‑1,‑3,‑4 deliberately.
• Thinking Cherenkov telescopes are located in tropical regions for better weather: Ladakh is cold desert, not tropical. The advantage is high altitude and dry air, not warmth. Remember the location – “Hanle, Ladakh” is north of 30°N.

Memory Aids & Mnemonics

1. “R2D2” for EM band applications (observe pattern)

• R – Radio waves (AM, FM)
• 2 – Microwaves (2.4 GHz, 5 GHz – but think of “2” as “2nd band”)
• D – Infrared (Remote controls, “D” for device control)
• 2 – Visible light (two eyes – visible)
• U – Ultraviolet (UV, “U” for umbrella – protection)
• X – X‑rays (medical)
• G – Gamma rays (cancer therapy)

You can chain them: “R‑2‑D‑2‑U‑X‑G”. For the question about remote control, recall that “D” (infrared) is the one used for device control.

2. “P.A.B.T” for pressure units

• P – Pascal
• A – Atmosphere (atm)
• B – Bar
• T – Torr (mm Hg)

Add “S” for psi (pound per square inch) – “P.A.B.T.S.” The mnemonic is “Press A Button Two Times” – but that’s contrived. Better: “Papa And Baby Twin” works. Extend with “S” – “Papa And Baby Twin Sleep” for psi. Practise it until instant recall.

3. “Lo‑Sky, Hi‑Space” for propagation modes

• Low frequency – uses Sky wave (ionosphere)
• High frequency (above 30 MHz) – uses Space wave (line‑of‑sight)

UHF is “Hi” – so Space wave.

Quick Revision

Introduction

• Physics subtopic in RPSC covers wave properties, measurement units, biological applications, and current science‑tech milestones.
• 7 PYQs from 2016–2024; moderate difficulty, mix of factual and analytical.

Core Concepts & Foundations

• Electromagnetic spectrum: radio‑microwave‑IR‑visible‑UV‑X‑ray‑gamma. Each band has distinct applications.
• UHF (300 MHz–3 GHz) propagates via space waves; sky waves and ground waves are ineffective.
• Pressure = Force/Area. SI unit Pascal; other common units: atm, bar, torr, psi, dyn/cm².
• Cataract is caused by denaturation of lens protein (crystallins).
• Sound in a stethoscope travels by multiple reflection off tube walls.
• Solar Impulse‑2 first solar circumnavigation.
• Hanle Cherenkov Observatory – uses mirrors to detect Cherenkov radiation from gamma‑ray showers; located in Ladakh (cold desert, not tropical).

Deep‑dive sections

• Remote controls use infrared (safe, invisible, cheap LED).
• UHF uses space waves; frequencies > 30 MHz need line‑of‑sight.
• Cataract – protein aggregation scatters light.
• Pressure units – at least five major ones, all valid.
• Stethoscope – multiple reflection is key, not refraction/diffraction/polarisation.
• Solar Impulse‑2 – 17,000 solar cells, circumnavigated in 2015‑16.
• Hanle – Asia’s largest Cherenkov telescope, altitude 4,300 m.

Worked Examples

• All 7 PYQs solved with step‑by‑step reasoning and correct answers in prose.

PYQ Trends & Patterns

• Wave physics dominates (4/7). Contemporary science (Solar Impulse, Hanle) features twice. Pressure units, cataract appear once.
• Factual recall > analytical reasoning (5 vs 2).
• Formats: single‑best‑answer, combined‑option, statement‑based.

What Else Could Be Asked

• Microwaves in Wi‑Fi; stethoscope diaphragm principle; molecular detail of cataract; sky wave propagation for AM; matching pressure units to fields; other Indian observatories; reasons for high‑altitude observatory sites.

Common Mistakes & Traps

• Confusing IR with UV; assuming all radio uses sky waves; thinking cataract is fat deposition; mixing force and pressure units; assuming TIR in stethoscope; confusing Solar Impulse‑1 with 2; tropical vs. cold desert for Hanle.

Memory Aids & Mnemonics

• “R2D2-UXG” for EM band applications.
• “P.A.B.T.S” for pressure units (Pascal, Atmosphere, Bar, Torr, psi).
• “Lo‑Sky, Hi‑Space” for propagation modes.