The current will be allowed to flow and this current flow in the secondary will have an immediate influence on the primary. This is similar to the third law of Newton, for any action there is a reaction equal and opposite to it. On the other hand a magnet, itself attracts ferrous metals like iron, but it does not do any good on copper. We can never produce magnetic field by copper unless we draw some current through it. Metal detectors also behave in the same way.
Electromagnetic waves are the same as radio waves.
In metal detectors radio waves are around 20 Khz, it means that they have wave length of 15 km. Medium wave is around 200m to 1Km and short-wave around 200 m to 10 meter, VHF and FM around 1 to 3 meter and Radar Penetration systems usually around less that 30 Cm. But all are the same called Radio Waves. They are all the same electromagnetic waves but can behave differently in different environments. For example Long Wave travels in ground better than air.