Why must humans limit their exposure to X-rays and gamma rays?

The speed of light in a material is 0.50 c. what is the critical angle of a light ray at the interface between the material and a vacuum?

Determine el momento angular de un rueda de 3000g moviendose a 10m/s con un radio de giro de 400cm

In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. what is the electron's orbital frequency? what is the effective current of the electron?