Key Equations
Progressive Waves — AQA A-Level Physics
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Wave equation
$$v = f\lambda$$
- Where:
- $v$ = wave speed (m \(s^{-1}\))
- $f$ = frequency (Hz)
- $\lambda$ = wavelength (m)
Applies to all waves. For EM waves in a vacuum, v = c = \(3 \times 10^{8}\) m/s.
Intensity-amplitude relationship
$$I \propto A^{2}$$
- Where:
- $I$ = intensity (W \(m^{-2}\))
- $A$ = amplitude (m)
Doubling amplitude quadruples intensity. Used in interference and diffraction analysis.
Frequency-period relationship
$$f = \frac{1}{T}$$
- Where:
- $f$ = frequency (Hz)
- $T$ = period (s)
Read T from a displacement-time graph as the time for one complete cycle.