Aspirant Academy

Science and Technology

Key Points at a Glance

Physics: Motion, Work/Power/Energy, Gravitation, Light, Heat, Electricity, Magnetism, Sound, EM Waves, Medical Diagnostics, Nuclear Fission/Fusion, Radiation Safety

Paper II · Unit 2 Section 1 of 13 0 PYQs 31 min
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Key Points at a Glance

  1. Newton's Laws of Motion

    • First Law (Law of Inertia): body at rest or in uniform motion continues unless acted upon by an external force
    • Second Law: F = ma (force = mass × acceleration)
    • Third Law: for every action there is an equal and opposite reaction

  2. Law of Conservation of Energy

    • Energy can neither be created nor destroyed — it can only be converted from one form to another
    • Total mechanical energy (KE + PE) is conserved in the absence of non-conservative forces

  3. Newton's Law of Gravitation

    • F = Gm₁m₂/r² where G = 6.674 × 10⁻¹¹ N·m²/kg²
    • Escape velocity from Earth = 11.2 km/s; from Moon = 2.4 km/s
    • Moon has no atmosphere because its escape velocity is too low to retain gas molecules

  4. Light and Its Phenomena

    • Light travels at 3 × 10⁸ m/s in vacuum
    • Reflection: angle of incidence = angle of reflection
    • Refraction: bending at medium boundary; refractive index n = c/v
    • Total Internal Reflection (TIR): basis of optical fibres and diamond brilliance; critical angle for glass ≈ 42°

  5. Laws of Thermodynamics

    • Zeroth Law: thermal equilibrium concept — defines temperature
    • First Law: energy conservation; Q = ΔU + W
    • Second Law: heat flows naturally from hot to cold; entropy increases; no heat engine is 100% efficient

  6. Ohm's Law and Electrical Energy

    • Ohm's Law: V = IR (voltage = current × resistance)
    • Power: P = VI = I²R = V²/R
    • Joule's Law of Heating: H = I²Rt
    • SI unit of electrical energy: kilowatt-hour (kWh); 1 kWh = 3.6 × 10⁶ J (one "unit" on electricity bill)

  7. Electromagnetic Induction

    • Faraday (1831): a changing magnetic flux through a circuit induces an EMF
    • Principle behind generators, transformers, and induction motors
    • Lenz's Law: the induced current opposes the change causing it (negative sign in Faraday's law)

  8. Sound Waves

    • Sound is a mechanical longitudinal wave requiring a material medium
    • Speed in air: 332 m/s at 0°C; ≈ 346 m/s at 25°C
    • Ultrasound (> 20,000 Hz): used in sonar, medical imaging, industrial flaw detection
    • Infrasound (< 20 Hz): detected by elephants; used in seismic monitoring

  9. Electromagnetic Spectrum

    • Order by increasing frequency: Radio → Microwaves → Infrared → Visible (VIBGYOR) → Ultraviolet → X-rays → Gamma rays
    • All EM waves travel at c = 3 × 10⁸ m/s in vacuum
    • They differ in frequency and wavelength; relation: c = fλ

  10. Medical Imaging — X-ray, CT, MRI

    • X-rays (Röntgen, 1895): penetrate soft tissue but absorbed by bones and metal; used for skeletal imaging
    • CT Scan: multiple X-ray images from different angles reconstructed into 3D cross-sections
    • MRI: uses strong magnetic fields (1.5–3 Tesla) and radio waves; images soft tissue without any radiation

  11. PET Scan and Ultrasound

    • PET Scan: uses F-18 fluorodeoxyglucose (FDG); cancer cells consume more glucose → appear as "hot spots"
    • Positron emitted by F-18 annihilates with electron → two gamma photons detected
    • Ultrasound (USG): 2–15 MHz sound waves reflected from internal organs; safe in obstetrics and cardiac imaging

  12. Radiation Safety — ALARA

    • ALARA principle: As Low As Reasonably Achievable
    • Time: minimise exposure duration
    • Distance: intensity ∝ 1/d²
    • Shielding: lead aprons for X-rays, concrete for nuclear reactors
    • Annual permissible dose for radiation workers = 20 mSv/year (ICRP)

  13. Kepler's Laws of Planetary Motion

    • First Law: planets move in elliptical orbits with the Sun at one focus
    • Second Law: a line from Sun to planet sweeps equal areas in equal times (conservation of angular momentum)
    • Third Law: T² ∝ r³ (square of period proportional to cube of semi-major axis)

  14. Semiconductor Physics and Band Theory

    • Conductors: overlapping valence and conduction bands (zero band gap)
    • Insulators: large band gap (> 3 eV)
    • Semiconductors (Si, Ge): small band gap (~1 eV); conductivity increases with temperature
    • p-n junction diode: allows current in one direction only (rectification)
    • LED: converts electrical energy to light at a p-n junction