Physics: Core Concepts, One Worked Numerical, and Mark-Losing Traps
What the physics section tests
SRMHCAT physics draws on the Class 11–12 core: kinematics and laws of motion, work–energy, rotational motion, gravitation, SHM and waves, heat and thermodynamics, electrostatics and current electricity, ray optics, and modern physics such as the photoelectric effect and atomic models. Questions are usually single-concept numericals or short conceptual checks, so dimensional awareness matters more than long derivations.
Core rules to keep ready
- Use g = 9.8 m/s² unless the paper states 10; keep signs consistent with your chosen positive direction.
- For projectiles, horizontal and vertical motions are independent: x = u cosθ·t, y = u sinθ·t − ½gt². Maximum range occurs at 45° when launch and landing heights are equal.
- Series resistances add; parallel conductances add. For two resistors in parallel, R = R₁R₂/(R₁+R₂).
- Snell's law: n₁ sin i = n₂ sin r. Total internal reflection needs n₁ > n₂ and i greater than the critical angle sin⁻¹(n₂/n₁).
- Photoelectric equation: hν = φ + K_max. Stopping potential depends on frequency, not on intensity.
Worked example
Two resistors, 6 Ω and 3 Ω, are connected in parallel across a 12 V battery. Find the total current. Parallel resistance: R = (6×3)/(6+3) = 18/9 = 2 Ω. Current I = V/R = 12/2 = 6 A. Check with branch currents: 12/6 = 2 A and 12/3 = 4 A; these sum to 6 A, consistent.
Traps that cost marks
- Mixing cm and m inside one formula; convert before substituting.
- Using degrees in equations that require radians, such as SHM phase terms.
- Assuming heavier objects fall faster; ignore air resistance only when the question says so.
- Forgetting that parallel branches share voltage, not current.
- Dropping the sign on deceleration or on a charge in an electric field.