All waves are either progressive (travelling) or stationary (standing). Progressive waves move continuously through a medium (or vacuum for electromagnetic waves) transferring energy from one region to another.
2. Transverse vs Longitudinal Waves★★☆☆☆⏱ 12 min
Progressive mechanical waves are classified based on the direction of particle oscillation relative to the direction the wave travels.
3. Key Parameters and the Wave Equation★★★☆☆⏱ 15 min
All progressive waves can be described by standard parameters that define their size, timing, and speed:
**Amplitude ($A$):** Maximum displacement of a particle from equilibrium (unit: m).
**Wavelength ($\lambda$):** Distance between two consecutive points that are in phase (unit: m).
**Period ($T$):** Time for one full wave cycle to pass a point (unit: s). $T = 1/f$
**Frequency ($f$):** Number of full cycles passing a point per second (unit: Hz). $f = 1/T$
**Wave speed ($v$):** Distance the wave travels per unit time (unit: m/s).
The fundamental relationship between these parameters applies to all progressive waves, regardless of type:
v = f \lambda
4. Phase Difference★★★★☆⏱ 10 min
Phase describes the current position in the oscillation cycle of a particle on a wave. Phase difference is the difference in phase between two points on the same wave, measured in radians or degrees.
For two points separated by distance $\Delta x$ on a wave of wavelength $\lambda$, the phase difference $\Delta \phi$ is calculated as:
\Delta \phi = \frac{2\pi \Delta x}{\lambda}
Common Pitfalls
Why: This is the most common misconception examiners test for this topic.
Why: Classification depends on direction relative to wave travel, not absolute direction.
Why: The ratio of distances will be wrong if units don't match, leading to incorrect phase difference.
Why: Simple algebraic error common under exam pressure, costing easy marks.