2. what is the frequency of a 6.9 x 10-13 m wave?
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frequency =v/π= 3×10^8/6.9 ×10^-13=5×10^20

Explanation: the relationship between the velocity and frequency of a wave is V=fπ ,where V=velocity of wave while the π or lander represents wavelength which was given in the question.f represents frequency of wave.velocity of waves differs,e.g sound waves has a velocity of 330m/s while electromagentic spectrum waves eg UV,infrared has a constant velocity called velocity of light =3×10^8.the question did not clarify the type of wave so I assumed it should be light. Which has a V= 3×10^8.so frequency was calculate d using velocity divided by wavelength (which. Was given).