Physics - Formulas, Units and Applied Reasoning
What the section tests
Physics contributes 25 one-mark questions and rewards formula recall plus unit discipline rather than lengthy derivation. Expect short numericals and one-line conceptual items drawn from the diploma physics course.
Core areas and rules
- Units and dimensions: force MLT⁻², energy ML²T⁻², power MLT⁻³; an equation is valid only if dimensions balance on both sides.
- Mechanics: equations of motion, work–energy theorem, conservation of momentum, friction, circular motion, moment of inertia of standard bodies.
- Oscillations and sound: SHM period, simple pendulum T = 2π√(l/g), beats, resonance, Doppler shift.
- Heat: specific and latent heat, thermal expansion, first law of thermodynamics, Carnot efficiency = 1 − T₂/T₁ with temperatures in kelvin.
- Electricity and magnetism: Ohm's law, series and parallel networks, Kirchhoff's laws, F = BIL sinθ, electromagnetic induction.
- Modern physics and electronics: photoelectric equation, Bohr levels, intrinsic versus extrinsic semiconductors, p–n junction rectification.
Worked example
A lamp rated 100 W, 250 V runs at its rated voltage. Resistance R = V²/P = 250²/100 = 625 Ω, and current I = P/V = 100/250 = 0.4 A. If the same lamp is run at 200 V, power = V²/R = 40 000/625 = 64 W. Options frequently quote this off-rating value instead of the rated 100 W, so compute it rather than assuming.
Traps that cost marks
- Peak versus RMS: the 230 V supply is RMS, so the peak is 230√2 ≈ 325 V.
- Entering Celsius into the Carnot expression instead of kelvin.
- Confusing gauge pressure with absolute pressure (gauge + atmospheric).
- Forgetting that frequency stays constant while wavelength and speed change when light or sound enters a new medium.
- Writing the photoelectric equation with frequency on one side and wavelength on the other without converting.