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The Wave Equation [3] The speed ( v ) that a wave pulse travels at and the frequency of the continuous wave ( f ) determine the wavelength ( ) of the wave speed = distance/time [distance = , time is the period = T] v=/T v = wave speed [ms-1]; = wave length [m]; T = period [s]; v=f f = frequency [Hz] Example 1. Red light of frequency 3.95x1014 Hz has a wavelength of 760 nm. What is the speed of light? [760 nm = 760x10-9 m] v = f = 3.95x1014(760x10-9) 3.00x108 ms-1 Example 2. Sound waves travel at 334 ms-1 in air. What is the wavelength of a sound produced by a 256 Hz tuning fork? v = f … = v/f = 334/256 1.30 m Example 3. A ripple tank generator is set at 24 Hz. Measurement of the ripple wave produced has the distance between wavefronts as 2.5 cm. What is the speed of the water waves? f = 24 Hz [same as source] and = 0.025 m [distance between successive crests] v = f = 24(0.025) = 0.60 ms-1 Example 4. An AM radio-wave has a wavelength of 100 metres. Given that radiowaves travel at the speed of light [3.0x108 ms-1], what is the frequency of this radio signal [in MHz]? = 100 m v = 3.0x108 ms-1 v = f … f = v/ = 3.0x108/100 = 3.0x106 Hz f = 3.0 MHz