NTPC ALP Group D

Physics for RRB Exams

Units & Measurements

SI Units

Length: Meter (m)

Mass: Kilogram (kg)

Time: Second (s)

Current: Ampere (A)

Temperature: Kelvin (K)

Force: Newton (N)

Work/Energy: Joule (J)

Power: Watt (W)

Pressure: Pascal (Pa)

Scalar vs Vector

• Scalar (Magnitude only): Distance, Speed, Mass, Energy, Time
• Vector (Magnitude + Direction): Displacement, Velocity, Force, Acceleration, Momentum

Motion & Force

Newton's Laws of Motion

• First Law (Inertia): Object remains at rest/motion unless acted upon by external force.
• Second Law (F=ma): Force equals mass times acceleration.
• Third Law: For every action, there is an equal and opposite reaction.

Equations of Motion

• v = u + at
• s = ut + ½at²
• v² = u² + 2as
(u=initial velocity, v=final velocity, a=acceleration, t=time, s=displacement)

Work, Energy & Power

Key Concepts

• Work (W): Force × Displacement × cosθ (Unit: Joule)
• Kinetic Energy (KE): ½mv²
• Potential Energy (PE): mgh
• Power (P): Work / Time (Unit: Watt)
• 1 Horsepower (HP): 746 Watts

Light & Sound

Light (Optics)

• Reflection: Angle of incidence = Angle of reflection
• Refraction: Bending of light (Snell's Law)
• Convex Lens: Converging (used for Hypermetropia/Long-sightedness)
• Concave Lens: Diverging (used for Myopia/Short-sightedness)
• Speed of Light: 3 × 10⁸ m/s

Sound

• Longitudinal wave (needs medium)
• Speed: Solids > Liquids > Gases
• Audible Range: 20 Hz to 20,000 Hz
• Ultrasonic: > 20,000 Hz (Bats, SONAR)
• Infrasonic: < 20 Hz (Earthquakes)

Electricity

Ohm's Law

V = IR (Voltage = Current × Resistance)

• Series Combination: R = R₁ + R₂ + ...
• Parallel Combination: 1/R = 1/R₁ + 1/R₂ + ...
• Fuse Wire: High resistance, low melting point (Lead-Tin alloy)

Test Your Knowledge

30 random questions • 1 minute per question