Physics: Mechanics, Electricity and Modern Physics
What you must understand
Agniveer-level physics centres on units and dimensions, kinematics and Newton's laws, work-energy and momentum, heat and thermodynamics basics, waves and sound, electricity and magnetism (Ohm's law, series/parallel, power), and light and modern physics (reflection, refraction, photoelectric effect, atomic models).
Traps to expect
- Unit conversion hidden in numbers (cm to m, g to kg). Always convert before substituting.
- Series vs parallel: in series, current is common and voltage divides; in parallel, voltage is common and current divides. Reversing this is the commonest error.
- Sign conventions in kinematics: deceleration is negative acceleration; keep directions consistent.
- Formula recall without conditions: e.g. v = u + at applies only for constant acceleration.
Rule of thumb
Write the given quantities with units, write the unknown, then pick the formula that links them. Check the dimension of your answer against the expected unit.
Worked example
Two resistors 4 Ω and 6 Ω in parallel across 12 V. Parallel resistance = (4×6)/(4+6) = 2.4 Ω. Current = V/R = 12/2.4 = 5 A. Note each branch draws 3 A and 2 A respectively - they add, confirming the result.
Practice habit
Memorise the SI units table and the power formulas (P = VI = I²R = V²/R); these recur every year.