KCET Physics - Formula Fluency, Signs, and Speed
KCET Physics supplies 60 of the 180 one-mark questions, drawn strictly from the first and second PUC syllabus (NCERT Class 11–12). There is no negative marking, so every question should be attempted, and the 80 minutes shared with Chemistry and either Mathematics or Biology leave roughly 25–27 seconds per question. The paper rewards rapid recall of standard results and clean sign conventions far more than long derivations.
Core rules to keep loaded
- On an incline, resolve weight into mg sinθ along the plane and mg cosθ perpendicular to it; static friction equals the applied force up to its maximum μN.
- Terminal voltage of a cell is V = ε − Ir; the junction rule is charge conservation and the loop rule is energy conservation.
- The mirror/lens relation 1/v − 1/u = 1/f follows the Cartesian convention: distances measured against the incident light are negative.
- Photoelectric effect: E = hν = hc/λ; stopping potential tracks frequency, photocurrent tracks intensity.
- Beats and resonance come from superposition; a receding source lowers the observed frequency (Doppler).
Worked example
A cell of emf 2 V and internal resistance 0.5 Ω is connected across a 1.5 Ω resistor. Total resistance is 2.0 Ω, so I = 2/2.0 = 1 A. Terminal voltage is V = ε − Ir = 2 − (1)(0.5) = 1.5 V. The resistor dissipates I²R = 1.5 W and the cell loses I²r = 0.5 W inside; together they equal εI = 2 W, confirming energy balance.
Traps that cost marks
Brighter light raises photocurrent but leaves stopping potential unchanged. In optics, concave and convex mirrors differ only by the sign of f, and candidates lose marks by mixing object-distance conventions. In collisions, momentum is conserved always but kinetic energy only when the collision is elastic. Drift velocity is a few millimetres per second yet current is large because free-electron density is enormous. Finally, g varies as 1/(R+h)², not linearly with height.