IIT JAM Physics: Mechanics, Fields, Waves and Quanta
IIT JAM PH tests mechanics, waves and optics, thermodynamics, electromagnetism, quantum mechanics and basic modern physics. Numerical questions often turn on units, sign conventions and the difference between peak and average quantities.
Core rules and concepts
- Mechanics: Newton’s laws, conservation of energy and momentum, rotational dynamics and simple harmonic motion; restoring force F = −kx gives ω = √(k/m).
- Waves and optics: superposition, interference and diffraction; lens/mirror equations use sign conventions; fringe spacing in Young’s double slit is β = λD/d.
- Thermodynamics: first law ΔU = Q − W; entropy increases for irreversible processes in an isolated system; Carnot efficiency η = 1 − T_c/T_h.
- Electromagnetism: Gauss’s law, Faraday’s law, Lenz’s law, Lorentz force F = q(E + v × B), and circuit rules.
- Quantum physics: photon energy E = hf = hc/λ; photoelectric threshold depends on work function; de Broglie wavelength λ = h/p; uncertainty principle.
- Modern physics: Bohr energy levels, nuclear binding, and basic solid-state band ideas.
Worked example
Find the energy of a photon with wavelength 500 nm. Use hc ≈ 1240 eV·nm. Then E = hc/λ = 1240/500 = 2.48 eV. In SI units, f = c/λ = 3.0×10⁸/(500×10⁻⁹) = 6.0×10¹⁴ Hz, and E = hf gives the same result after converting joules to eV.
Traps that cost marks
Do not mix rms and peak values in AC circuits. Apply sign conventions consistently for mirrors and lenses; a real image is not always inverted in every setup. Photon energy is inversely proportional to wavelength, not directly proportional. Convert eV and joules explicitly. Check whether a calculated image is real or virtual before choosing signs.
Key points
- Photon energy E = hc/λ; 1240 eV·nm is a useful shortcut.
- SHM frequency depends on √(k/m).
- Carnot efficiency uses absolute temperatures.
- Lenz’s law opposes the change in magnetic flux.
- rms values are not peak values in AC power.