Applied Science is the bridge between pure science and everyday engineering problems faced on Indian Railways.
It deals with the practical application of Physics, Chemistry & Biology in maintaining rolling stock, signalling, track, power-supply and environmental safety. Whether you are calculating traction motor torque, selecting coolants for diesel engines, or disinfecting coaches, you are using Applied Science. A sound grasp of basic laws, units, materials and safety norms is therefore essential for every RRB candidate.

The Railway syllabus compresses three years of science into 10–12 concise topics: Mechanics (laws of motion, friction, simple machines), Heat & Thermodynamics (boilers, refrigeration, calorific value), Sound & Light (signals, lamps, fibre-optic communication), Electricity (Ohm’s law, AC/DC machines, earthing), Magnetism (relays, traction), Modern Physics (semiconductors, lasers), Inorganic Chemistry (metals, alloys, corrosion, lubricants), Organic Chemistry (fuels, polymers, paints), Environmental Chemistry (pollution norms, CNG, SCR), Human Physiology (first-aid, hygiene, occupational diseases) and Plant Biology (bio-toilets, afforestation). Questions rarely go beyond 10+2 level, but they test speed, units, ratio-percentage and direct application rather than deep derivation. The golden rule: “Formula → Railway context → Closest option”.

Practice Set – 25 MCQs

1. [Easy] The unit of work in SI system is
   A) Newton
   B) Watt
   C) Joule
   D) Pascal

2. [Easy] Which of the following is not a vector quantity?
   A) Displacement
   B) Velocity
   C) Speed
   D) Acceleration

3. [Easy] The boiling point of water at 1 atm pressure is
   A) 0 °C
   B) 100 °C
   C) 212 °C
   D) 373 K

4. [Easy] Dry ice is the solid form of
   A) H₂O
   B) CO₂
   C) N₂
   D) O₂

5. [Easy] The chemical formula of common salt is
   A) NaHCO₃
   B) Na₂CO₃
   C) NaCl
   D) CaCl₂

6. [Easy] Which colour of light has the longest wavelength?
   A) Violet
   B) Blue
   C) Red
   D) Green

7. [Easy] The human normal body temperature is about
   A) 37 °C
   B) 98 °C
   C) 37 °F
   D) 27 °C

8. [Easy] Ohm’s law states that
   A) V = I R
   B) P = V I
   C) H = I² R t
   D) F = q v B

9. [Easy] Which gas is filled in electric bulbs to increase life?
   A) Oxygen
   B) Hydrogen
   C) Nitrogen-Argon mixture
   D) Chlorine

10. [Easy] The SI unit of frequency is
    A) Hertz
    B) Ampere
    C) Coulomb
    D) Joule

11. [Medium] A 220 V, 100 W bulb is connected to 110 V. The power consumed will be
    A) 100 W
    B) 50 W
    C) 25 W
    D) 200 W

12. [Medium] A diesel locomotive emits maximum quantity of
    A) CO₂
    B) CO
    C) NOₓ
    D) SPM

13. [Medium] The alloy used for heating elements of electric irons is
    A) Brass
    B) Nichrome
    C) Bronze
    D) Solder

14. [Medium] Bio-toilets in coaches use anaerobic bacteria originating from
    A) Cow dung
    B) Blue-green algae
    C) River sludge
    D) Hot-spring

15. [Medium] The traction motor of WAP-7 is cooled by
    A) Forced air
    B) Natural air
    C) Water
    D) Hydrogen

16. [Medium] Corrosion of railway tracks is basically
    A) Oxidation
    B) Reduction
    C) Displacement
    D) Neutralisation

17. [Medium] The pitch of a sound is determined by its
    A) Amplitude
    B) Frequency
    C) Speed
    D) Wavelength

18. [Medium] Head lights of trains use concave mirrors to
    A) Widen the beam
    B) Focus the beam
    C) Invert the image
    D) Dim the light

19. [Medium] Which fuel has the highest calorific value?
    A) Petrol
    B) Diesel
    C) CNG
    D) Hydrogen

20. [Medium] The dangerous pollutant CO binds with haemoglobin and forms
    A) Carboxy-haemoglobin
    B) Oxy-haemoglobin
    C) Meth-haemoglobin
    D) Ferri-haemoglobin

21. [Hard] A capacitor of 4 µF is connected to 200 V supply. The energy stored is
    A) 0.08 J
    B) 0.04 J
    C) 0.02 J
    D) 0.16 J

22. [Hard] The tractive effort of a locomotive is 400 kN and speed is 72 km/h. The power developed is
    A) 8000 kW
    B) 4000 kW
    C) 2880 kW
    D) 800 kW

23. [Hard] A diesel engine has compression ratio 16 : 1 and expansion ratio 8 : 1. The cut-off ratio is
    A) 2
    B) 4
    C) 8
    D) 16

24. [Hard] The relative humidity in an AC coach is maintained around
    A) 25 %
    B) 55 %
    C) 85 %
    D) 95 %

25. [Hard] In fiber-optic signalling the core refractive index is 1.5 and cladding 1.45. The critical angle is nearest to
    A) 45°
    B) 60°
    C) 75°
    D) 90°

Answers

1. Answer

   Correct: Option C. Work = Force × Displacement; Joule (J) is the SI unit.
2. Answer

   Correct: Option C. Speed has magnitude only; others have direction too.
3. Answer

   Correct: Option B. By definition, 100 °C at 1 atm.
4. Answer

   Correct: Option B. Solid CO₂ sublimates at –78 °C.
5. Answer

   Correct: Option C. Sodium chloride.
6. Answer

   Correct: Option C. Red light ≈ 700 nm, longest in visible spectrum.
7. Answer

   Correct: Option A. 37 °C (98.6 °F).
8. Answer

   Correct: Option A. V = I R is Ohm’s law.
9. Answer

   Correct: Option C. Inert N₂-Ar mixture prevents filament oxidation.
10. Answer

    Correct: Option A. Hertz (Hz) = cycles per second.
11. Answer

    Correct: Option C. P ∝ V²; (110/220)² × 100 = 25 W.
12. Answer

    Correct: Option A. Complete combustion gives CO₂ in largest volume.
13. Answer

    Correct: Option B. Nichrome (Ni-Cr-Fe) has high resistivity & melting point.
14. Answer

    Correct: Option A. Inoculum taken from cow dung; bacteria digest waste.
15. Answer

    Correct: Option A. Forced-air blower keeps motor within 120 °C.
16. Answer

    Correct: Option A. Iron converts to Fe₂O₃/rust—oxidation.
17. Answer

    Correct: Option B. Higher frequency → higher pitched sound.
18. Answer

    Correct: Option B. Concave mirror converges light into parallel beam.
19. Answer

    Correct: Option D. Hydrogen ≈ 150 MJ/kg, highest among choices.
20. Answer

    Correct: Option A. CO + Hb → Carboxy-haemoglobin, blocking O₂.
21. Answer

    Correct: Option A. E = ½ C V² = 0.5 × 4×10⁻⁶ × (200)² = 0.08 J.
22. Answer

    Correct: Option A. P = F × v = 400 kN × 20 m/s = 8000 kW.
23. Answer

    Correct: Option A. Cut-off ratio = compression/expansion = 16/8 = 2.
24. Answer

    Correct: Option B. 50–60 % RH gives comfort without condensation.
25. Answer

    Correct: Option C. sinθc = n₂/n₁ = 1.45/1.5 → θc ≈ 75°.

Quick Shortcuts & Tips

• Units first: Railway values are always in SI (kW, kN, m/s). Convert km/h → m/s by ×5/18.
• Power triangle: P = F × v is favourite for traction Qs—memorise 1 kN × 1 m/s = 1 kW.
• Bulb power ∝ V²: Half voltage → one-fourth power (Q-11).
• Capacitor energy: ½ C V²—don’t forget the ½; RRB loves this trap.
• Refractive index: Remember sinθc = n₂/n₁; keep calculator in degree mode.
• Calorific value order: Hydrogen > CNG > Diesel > Petrol > Coal.
• Pollution chart: CO₂ (greenhouse), CO (poison), NOₓ (acid), SPM (lungs).
• Bio-toilet bacteria: Anaerobic → cow dung → methane + sludge—never choose aerobic.
• Mirror/Lens sign convention: Concave mirror → +f for real focus; always ask what happens to beam.
• Rule of 55: 55 % RH & 25 °C = AC coach set-point—appears as numeric option.