Progressive waves — common mistakes

Pay close attention to the direction of motion for Doppler Effect calculations! A source moving towards an observer causes a higher observed frequency (use '-' in the denominator for sound), while a source moving away causes a lower observed frequency (use '+' in the denominator).

A progressive wave is characterised by its continuous transfer of energy from one location to another, without any net transfer of the medium's matter itself. The disturbance (the wave) moves, but the medium's particles simply oscillate around their equilibrium positions.

No, sound waves are longitudinal waves, meaning their particle oscillations are parallel to the direction of energy transfer. Polarisation is a phenomenon exclusive to transverse waves, where oscillations can be restricted to a single plane.

A CRO displays a voltage-time graph of a signal. By connecting a microphone, you can view a sound wave. From the screen's time-base setting, you can measure the period (T) of the wave. From the period, you can calculate the frequency ($f = 1/T$). The amplitude of the wave can also be determined from the voltage scale (Y-gain).

A displacement-distance graph is like a photograph of the wave at one instant, showing the position of all particles. From it, you can find the wavelength. A displacement-time graph is like a video of a single particle, showing how its position changes over time. From it, you can find the period.