PHYSICS – SHORT NOTES

1. Units & Measurements

• Base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K).

• Derived units: velocity (m/s), force (N), energy (J).

• Significant figures → accuracy measure.

• Error types → systematic error, random error.

2. Motion (Kinematics)

Equations of Motion

• v = u + at

• s = ut + ½at²

• v² = u² + 2as

Key Points

• Speed = distance/time

• Velocity = displacement/time

• Acceleration = change in velocity/time

3. Laws of Motion

• 1st Law: Object remains at rest/motion unless force acts.

• 2nd Law: F = ma

• 3rd Law: Every action has equal + opposite reaction.

• Friction → opposes motion.

4. Work, Energy & Power

• Work = F × s

• Kinetic Energy = ½mv²

• Potential Energy = mgh

• Power = Work/Time

• Energy cannot be created or destroyed → only transformed.

5. Gravitation

• F = G (m₁m₂ / r²)

• g = 9.8 m/s²

• Weight = mg

• Free fall → only gravity acts.

6. Waves

• Wave speed = frequency × wavelength

• Transverse waves → particles move perpendicular

• Longitudinal waves → particles move parallel

• Sound needs medium; cannot travel in vacuum.

7. Light (Optics)

• Reflection: angle of incidence = angle of reflection

• Refraction: bending of light; n = sin i / sin r

• Lens formula: 1/f = 1/v + 1/u

• Mirror formula: 1/f = 1/v + 1/u

• Total internal reflection → occurs at high refractive index to low.

8. Electricity

• Ohm’s Law: V = IR

• Resistance in series: R_total = R₁ + R₂

• Resistance in parallel: 1/R = 1/R₁ + 1/R₂

• Power = VI

9. Magnetism

• Like poles repel, unlike poles attract

• Magnetic field lines go N → S outside magnet

• Right-hand thumb rule → direction of current & magnetic field

10. Modern Physics

• Photoelectric effect → light ejects electrons from metal

• E = mc²

• Atom has nucleus (protons + neutrons) & electrons around