NDA & CDS 2 2025 Exam Physics Revision Class 4

Introduction

Physics is the foundation of many scientific and technological advancements. For NDA CDS aspirants, a clear understanding of basic Physics concepts is not only essential for the written examination but also helpful in developing logical reasoning and problem-solving skills. In this revision, we will focus on some important topics—Laws of Motion, Reflection, Refraction, and the Human Eye—which frequently appear in the exam and hold great practical relevance in daily life.

Laws of Motion

Proposed by Sir Isaac Newton, the three laws of motion form the basis of classical mechanics.

1. First Law (Law of Inertia): A body continues to remain at rest or in uniform motion in a straight line unless acted upon by an external force.
2. Second Law: The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force (F = ma).
3. Third Law: For every action, there is an equal and opposite reaction.

These laws explain everything from why seatbelts are important in cars to how rockets launch into space.

Reflection of Light

Reflection is the bouncing back of light rays when they strike a polished surface like a mirror. It follows two main laws:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, reflected ray, and the normal all lie in the same plane.

Reflection is the principle behind mirrors, periscopes, and optical instruments.

Refraction of Light

Refraction occurs when light passes from one medium to another (like air to glass) and changes its speed, causing it to bend. It follows Snell’s Law: n1sin⁡i=n2sin⁡rn_1 \sin i = n_2 \sin rn1​sini=n2​sinr

where iii is the angle of incidence, rrr the angle of refraction, and nnn the refractive index.

Refraction explains phenomena like the apparent bending of a stick in water, the working of lenses, and the twinkling of stars.

The Human Eye

The human eye is a natural optical instrument that allows us to see the world. Its key parts include:

• Cornea and Lens: Focus light rays on the retina.
• Retina: Acts as a screen where the image is formed.
• Iris and Pupil: Control the amount of light entering the eye.

Common defects include myopia (short-sightedness), hypermetropia (long-sightedness), and astigmatism, which can be corrected using suitable lenses.

Understanding the eye helps in appreciating how optical instruments like cameras and microscopes are designed.

Conclusion

The topics of Laws of Motion, Reflection, Refraction, and the Human Eye are not only significant from an exam perspective but also vital in understanding the physical world. Mastery of these concepts strengthens analytical skills, improves problem-solving ability, and ensures better performance in the NDA CDS 2 2025 examination. With regular practice and conceptual clarity, aspirants can confidently tackle Physics questions and move one step closer to achieving their goal of serving the nation.