Error 1: Gamma rays travel faster than radio waves

Wrong thinking: Higher frequency = higher energy = faster wave. Correct: ALL EM waves travel at c = $3 \times 10^{8}$ m/s in vacuum. Energy per photon (E = hf) is higher for gamma rays, but wave speed is independent of frequency in vacuum. Only in a medium do different wavelengths travel at different speeds (dispersion).

Error 2: Displacement current = flow of electrons in capacitor gap

Wrong thinking: Displacement current is just electrons slowly drifting across the gap. Correct: There are NO charges crossing the gap. Displacement current Id = ε_{0}(dΦ_E/dt) is a mathematical quantity representing the effect of a changing electric field — it is not a physical current of charges.

Error 3: X-rays have higher frequency than gamma rays

Wrong thinking: X-rays in medical scanners seem powerful, so they must be highest frequency. Correct: Gamma rays (10^{18}–10^{24} Hz) have higher maximum frequency than X-rays (10^{16}–10^{21} Hz). The ranges DO overlap (10^{18}–10^{21} Hz). Classification is by source, not frequency.

Error 4: E and B in an EM wave are 90° out of phase

Wrong thinking: Since E and B are spatially perpendicular, they must be temporally out of phase. Correct: E ⊥ B in direction (spatial), but they oscillate IN phase (temporal). Peaks and zeros occur at the same instant at any given point.

Error 5: Visible light travels faster than other EM waves because we can "see" it

Wrong thinking: Visible light is special and faster. Correct: All EM waves travel at exactly c = $3 \times 10^{8}$ m/s in vacuum. The visible range is special only in that human eyes evolved to detect it.

Error 6: Infrared is used for sterilisation, UV for physiotherapy

Wrong thinking: Mixing up applications between IR and UV. Correct: IR is used for physiotherapy (deep heating) and night vision. UV is used for sterilisation and LASIK. Remember: IR = heat-related applications; UV = biological/chemical applications.

Error 7: Radiation pressure exists only for light (visible), not other EM waves

Wrong thinking: Radiation pressure is a property only of visible light. Correct: All EM waves carry momentum p = U/c and exert radiation pressure. The pressure is twice as large for perfectly reflecting surfaces (p = 2U/c) as for absorbing ones.

Error 8: Microwave ovens work by ionising food molecules

Wrong thinking: Microwaves have high energy like X-rays and ionise molecules. Correct: Microwaves cause ROTATION of polar molecules (especially water), generating heat through friction — not ionisation. Ionising radiation = UV, X-rays, gamma rays.