Light: Reflection — angle of incidence = angle of reflection. Two types of mirrors: Concave (converging — used in torches, headlights, solar cookers, shaving mirrors) and Convex (diverging — used in vehicle rear-view mirrors because they give wider field of view). Refraction — bending of light when passing from one medium to another. Lens types: Convex (converging — used in magnifying glasses, cameras, spectacles for hypermetropia) and Concave (diverging — used in spectacles for myopia/near-sightedness).

Electricity: Ohm's Law: V = IR (Voltage = Current × Resistance). Power: P = VI = I²R = V²/R. Energy: E = P × t. Series circuit: Same current flows through all components, total R = R₁+R₂+R₃. Parallel circuit: Same voltage across all components, 1/R = 1/R₁ + 1/R₂ + 1/R₃. Electric fuse: safety device that melts and breaks circuit when current exceeds safe limit.

Motion and Force: Speed = Distance/Time. Velocity = Displacement/Time (has direction). Acceleration = Change in velocity/Time. Newton's Laws: 1st (Inertia — object stays at rest/motion unless force acts), 2nd (F = ma), 3rd (every action has equal and opposite reaction). Friction: force opposing relative motion between surfaces. Types: static (before movement starts — highest), sliding, rolling (lowest). Friction can be reduced by lubrication, polishing surfaces, using ball bearings.

Sound: Produced by vibrations, needs medium to travel (cannot travel through vacuum). Speed: fastest in solids > liquids > gases. Human hearing range: 20 Hz to 20,000 Hz. Below 20 Hz: infrasonic (elephants can hear). Above 20,000 Hz: ultrasonic (dogs, bats can hear; used in medical imaging/sonography). Echo: reflection of sound, needs minimum distance of 17.2m at 20°C.

REET Exam Tips: 5 questions — focus on mirror/lens type-use matching (concave=torch, convex=rear-view), Ohm's Law calculations, Newton's three laws, and sound speed in different media (solid>liquid>gas).