RRB Group D · Bite-size lessons
Physics
About 6 min · General Science · English
Time worked out from the lesson's 399 words at 150 words a minute, plus a minute for each question.
The exam tests basic physics concepts from classes 9–10, focusing on practical applications and fundamental principles rather than complex problem-solving.
Key ideas
- Motion and Force: An object remains at rest or in uniform motion unless acted upon by an external force (Newton's First Law). Force equals mass times acceleration (F = ma). Every action has an equal and opposite reaction.
- Energy Conservation: Energy cannot be created or destroyed, only converted from one form to another. Kinetic energy (motion) and potential energy (position) constantly interchange in mechanical systems.
- Pressure Fundamentals: Pressure is force per unit area. It increases with depth in liquids. Atmospheric pressure at sea level is approximately 101,325 Pa or 1 atm. Pascal's law states that pressure applied to a confined fluid transmits equally in all directions.
- Heat Transfer: Heat flows from hot to cold bodies through conduction (solids), convection (fluids), and radiation (electromagnetic waves). Temperature measures average kinetic energy of particles.
- Wave Properties: Sound requires a medium to travel; light does not. Both exhibit reflection and refraction. Sound travels at 343 m/s in air; light travels at 3 × 10⁸ m/s in vacuum.
Watch out for
- Confusing mass and weight → Mass is the amount of matter (kg); weight is the gravitational force on that mass (N). Weight = Mass × g, where g ≈ 10 m/s².
- Mixing up reflection and refraction → Reflection is bouncing back from a surface (mirrors); refraction is bending when light enters a different medium (lenses, prisms).
- Wrong series/parallel resistance calculations → In series, resistances add directly. In parallel, reciprocals add. Students often add resistances directly in both cases.
Quick reference
- SI Base Units: Length (metre), Mass (kilogram), Time (second), Current (ampere), Temperature (kelvin)
- Newton's Laws: Inertia, F=ma, Action-Reaction
- Energy forms: Kinetic, Potential, Heat, Light, Sound, Electrical, Chemical
- Good conductors: Metals (silver, copper, aluminum); Poor conductors: Wood, rubber, plastic
- Convex lens converges light; Concave lens diverges light
Check yourself: 3 questions
1. A force of 20 N acts on a body of mass 5 kg. What is the acceleration produced in the body?
2. A train moving at 72 km/h applies brakes and comes to rest in 10 seconds. What is the retardation produced?
3. The resistance of a wire is 10 ohm. If the wire is stretched to double its length, what will be its new resistance? (Assume volume remains constant)
This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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