$V_{0}$ and intensity trap (Most common): Students say "doubled intensity → doubled $V_{0}$." Correct: $V_{0}$ = (hν − φ)/e has NO intensity term. $V_{0}$ is UNCHANGED. Only photocurrent changes.

Frequency doubling trap: If ν doubles, KE_max = h(2ν) − φ = 2hν − φ ≠ 2KE_max. KE_max does not double because of the constant −φ term. It would only double if φ = 0 (impossible).

Slope confusion: KE_max vs ν slope = h. $V_{0}$ vs ν slope = h/e. These are commonly swapped under exam pressure. Remember: $V_{0}$ = KE_max/e, so its graph slope is also divided by e.

Electron shortcut for protons: λ = 1.227/√V nm is derived using m_e and e_electron specifically. For protons or alpha particles, use λ = h/√(2mqV) with correct m and q. Never apply the shortcut to any particle other than electrons.

Below threshold with high intensity: No emission occurs below ν_{0} even at infinite intensity. Energy is quantised; one photon interacts with one electron. Multiple photons don't combine energy.

Photon rest mass: Photons have zero rest mass (m_{0} = 0). They have relativistic momentum p = h/λ = E/c. Do NOT apply E = m_{0}$c^{2}$ to photons; use E = pc.

Charge affecting de Broglie wavelength: λ = h/(mv) has no charge term. At the same velocity, an electron and a proton have very different λ only because of mass difference. Charge only matters when particles are accelerated through a potential (affects kinetic energy).

Work function units mismatch: If φ is in eV and E = hν is calculated in J (or vice versa), subtraction will give wrong KE_max. Always convert to the same units before computing KE_max = hν − φ.

Photoelectric vs Compton confusion: Photoelectric effect: photon completely absorbed, electron ejected. Compton effect: photon partially transfers energy to electron and scatters at reduced frequency. Different processes, different equations.

Threshold frequency uniqueness: ν_{0} = φ/h; each metal has a unique φ and therefore a unique ν_{0}. There is no single "threshold" that applies to all metals.