Hmm ... no, this is not part of Physics Module 6.
It has a bit to do with the discovery of electromagnetic waves by Heinrich Hertz in 1887, and bit of revision of Physics Module3 'Waves and Thermodynamics".
At the free ends of a wire, there cannot be any current (or else where is the current going to flow??) so the ends of a free wire must represent nodes (for the current) and anti-nodes (for the e.m.f.) of a standing wave.
If there is going to be a standing wave along the length of the wire, then the length of the wire will probably be equal to half the wavelength.
OK, so next we need the fundamental wave equation,
v= f λ and let v = c = 3 x 108 m/s and let λ/2 = 50 m
Therefore f = 3 Megahertz which of course corresponds to radio waves.