JEE · Physics · Modern Physics doubts

What does “Photoelectric effect” actually mean in Modern Physics, and why does it matter for JEE?

light ejects electrons from a metal only if its frequency exceeds a threshold, regardless of intensity.

I keep getting “Photoelectric effect” questions wrong in Modern Physics. What's the trap?

thinking very bright low-frequency light can eject electrons.

What does “Photon energy” actually mean in Modern Physics, and why does it matter for JEE?

light comes in packets of energy E = hf = hc/λ.

I keep getting “Photon energy” questions wrong in Modern Physics. What's the trap?

treating light purely as a wave when explaining the photoelectric effect.

What does “Bohr model” actually mean in Modern Physics, and why does it matter for JEE?

electrons occupy quantised orbits; for hydrogen E_n = −13.6/n² eV.

I keep getting “Bohr model” questions wrong in Modern Physics. What's the trap?

using a positive energy for a bound electron — bound states are negative.

What does “Mass–energy and binding energy” actually mean in Modern Physics, and why does it matter for JEE?

a nucleus weighs less than its parts; the missing mass becomes binding energy via E = Δmc².

I keep getting “Mass–energy and binding energy” questions wrong in Modern Physics. What's the trap?

ignoring the mass defect when computing nuclear energy.

What does “de Broglie wavelength” actually mean in Modern Physics, and why does it matter for JEE?

every particle has a wavelength λ = h/p, significant only for tiny masses.

I keep getting “de Broglie wavelength” questions wrong in Modern Physics. What's the trap?

expecting everyday objects to show wave behaviour (their λ is unimaginably small).

What is the difference between nuclear fission and nuclear fusion?

Fission splits a heavy nucleus into lighter ones (reactors); fusion joins light nuclei into a heavier one (the Sun) — both release energy.

What is the difference between n-type semiconductor and p-type semiconductor?

n-type is doped to have extra free electrons (negative carriers); p-type is doped to have holes (positive carriers).

What is the difference between intrinsic semiconductor and extrinsic semiconductor?

Intrinsic is pure silicon/germanium; extrinsic is deliberately doped to boost conductivity.

When do I use E = hf = hc/λ in Modern Physics, and what does it mean?

energy of a photon.