Module 3 · Agniveer Science

Physics Basics

Motion, force, energy, light, sound, electricity, magnetism.

Motion · Force · Energy · Light · Sound · Electricity

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Learning Objectives

Understand the fundamental concepts of Physics Basics
Apply key formulas and techniques to solve problems
Practice with exam-level questions to build speed and accuracy

Key Concepts

What is Physics?

Physics is the fundamental science of matter, energy, and their interactions. In Agniveer and defence exams, physics questions cover basic concepts from mechanics, heat, light, sound, electricity, and magnetism. Questions are at the high school level — focus on concepts, laws, and everyday applications.

Key Topics in Physics

1. Motion and Newton's Laws: First law (inertia — an object at rest stays at rest, in motion stays in motion unless acted upon), Second law (F = ma — force equals mass times acceleration), Third law (action-reaction — every action has an equal and opposite reaction).

2. Work, Energy, and Power: Work = Force × Displacement (W = Fd cosθ). Kinetic Energy = ½mv², Potential Energy = mgh. Law of conservation of energy (energy cannot be created or destroyed, only transformed). Power = Work/Time.

3. Light — Reflection and Refraction: Law of reflection (angle of incidence = angle of reflection). Types of mirrors: concave (converging), convex (diverging). Refraction — bending of light when passing from one medium to another. Snell's law: n₁sinθ₁ = n₂sinθ₂. Lenses: convex (converging), concave (diverging). Prism — dispersion of white light into 7 colours (VIBGYOR).

4. Sound: Sound travels as longitudinal waves. Speed of sound: 343 m/s in air (at 20°C), faster in liquids and solids. Amplitude → loudness, Frequency → pitch. Echo, SONAR, ultrasound, infrasound.

5. Electricity: Current (I) = V/R (Ohm's Law). Series circuits (current same, voltage divides) and parallel circuits (voltage same, current divides). Resistivity, heating effect (H = I²Rt), power (P = VI). AC vs DC, domestic circuits, fuse, earthing.

6. Magnetism: Bar magnet poles (North-South), magnetic field lines (from N to S outside magnet). Electromagnets — current-carrying wire creates magnetic field (Right-hand thumb rule). Earth as a magnet.

Solved Examples

Example 1 (Newton's Second Law)

A force of 20 N acts on a mass of 4 kg. What is the acceleration produced?

a) 2 m/s² b) 5 m/s² c) 10 m/s² d) 80 m/s²

Solution: b) 5 m/s². F = ma → 20 = 4 × a → a = 20/4 = 5 m/s².

Example 2 (Ohm's Law)

A current of 2 A flows through a resistor of 10 Ω. What is the voltage across the resistor?

a) 5 V b) 12 V c) 20 V d) 0.2 V

Solution: c) 20 V. V = IR = 2 × 10 = 20 V.

Example 3 (Refraction of Light)

When light passes from air to water, it bends:

a) Away from the normal b) Towards the normal c) Does not bend d) Depends on the colour of light

Solution: b) Towards the normal. Since water is optically denser than air, light slows down and bends towards the normal when entering water.

Shortcut Techniques

Remember formulas by their units — e.g., Newton = kg·m/s², Joule = N·m, Watt = J/s.
For optics, remember: Concave mirrors converge (used in torches, car headlights); Convex mirrors diverge (used in rearview mirrors).
For electricity: In series, resistance adds up (R_total = R₁ + R₂); in parallel, 1/R_total = 1/R₁ + 1/R₂.
Speed of sound is maximum in solids, minimum in gases. Speed of light is maximum in vacuum/air.

Pro Tip

In Agniveer exams, physics questions are direct application of formulas. Practice numericals from NCERT Class 9-10 science textbooks. Focus on conceptual understanding — why a bus needs more stopping distance than a car, why a straw appears bent in water, etc.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip

Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip

Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip

Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip

Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Practice Questions

Chemistry Basics →