General Science: Physics, Chemistry and Biology
Scope
Class 9-10 level science applied to everyday and railway contexts: motion and friction, work, power and energy, heat, mirrors and lenses, sound, current electricity and magnetism; acids, bases, salts and metals; cell structure, human body systems, vitamins and deficiency diseases.
Key concepts
- Newton's laws; friction opposes relative motion and is precisely what makes braking and wheel adhesion possible.
- Work = force × distance moved along the force (joule); Power = work/time (watt); energy is conserved.
- Ohm's law V = IR; resistances add in series and divide in parallel.
- pH below 7 is acidic, above 7 basic; acid plus base gives salt plus water.
- Deficiency one-liners: scurvy from vitamin C, rickets from vitamin D, night blindness from vitamin A, beri-beri from vitamin B1.
Worked example
A pump lifts 200 kg of water through 10 m in 20 s. Find its power (take g = 10 m/s²). Work = mgh = 200 × 10 × 10 = 20,000 J. Power = work/time = 20,000/20 = 1,000 W = 1 kW. Reasoning note: had the question given 200 N of weight instead of 200 kg of mass, the factor of 10 would be omitted and the answer would be 100 W. Read the unit before computing.
Traps that cost marks
- Confusing mass in kilograms with weight in newtons.
- Calling speed a vector: only velocity carries direction.
- Mixing the mirror and lens sign conventions, and forgetting that a convex lens converges.
- Confusing atomic number with mass number when identifying an element.
- Reversing a vitamin and its deficiency disease.