SSC CHSL · Bite-size lessons

Physics

About 6 min · General Awareness · English

Time worked out from the lesson's 365 words at 150 words a minute, plus a minute for each question.

The exam tests basic conceptual understanding rather than calculation-heavy problems. You need to know fundamental laws, units, SI units, key scientists and their discoveries, and real-world applications of physical principles.

Key ideas

• Newton's Laws of Motion: First law (inertia), second law (F = ma), third law (action-reaction). These govern all motion and force problems.
• Work, Energy and Power: Work is force × displacement in the direction of force. Energy is the capacity to do work. Power is the rate of doing work. Energy can neither be created nor destroyed (conservation law).
• Current Electricity: Current is the flow of charge (measured in amperes). Resistance opposes current flow. Ohm's law relates voltage, current and resistance: V = IR.
• Mirrors and Lenses: Concave mirrors converge light; convex mirrors diverge. Concave lenses diverge light; convex lenses converge. Real images can be projected on a screen; virtual images cannot.
• Reflection and Refraction: Reflection obeys angle of incidence = angle of reflection. Refraction is bending of light when it passes from one medium to another; governed by Snell's law.

Watch out for

• Confusing mass and weight: Mass is the amount of matter (kg); weight is the force due to gravity (N). Weight = mg, not just m.
• Wrong application of Ohm's Law: Students forget that Ohm's law applies only to ohmic conductors (constant resistance). Devices like diodes do not obey V = IR linearly.
• Sign convention in mirrors/lenses: Forgetting that distances measured against the direction of incident light are negative. For mirrors, object distance u is always negative; for real images v is negative (in front of mirror). Mixing up signs gives wrong image positions.

Quick reference

• Newton's Second Law: F = ma (force equals mass times acceleration).
• SI unit of Energy: Joule (J); 1 J = 1 N·m.
• Ohm's Law: V = IR (voltage = current × resistance).
• Speed of Light: 3 × 10⁸ m/s in vacuum; slows in denser media.
• Concave mirror: Converges light; forms real/virtual images depending on object position.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.

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