Why is electromagnetic wave dangerous?

Answer 1

Waves in the electromagnetic Spectrum are not usually dangerous. The EM spectrum goes all the way from Gamma and X-rays, which can be dangerous, to radio and microwaves, which can also be dangerous. It includes visible light, which can be dangerous also. However, you need quite a lot of it to pose a real threat, maybe except Gamma and X-rays. Maybe you mean an EMP (electromagnetic pulse). That is dangerous because it causes massive spikes in current in electronic equipment, destroying sensitive components such as microchips.