The frequency of a periodic signal is 20 mhz, state it's period?

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?

Examine the nuclear reacti why is this classified as a nuclear reaction rather than a chemical reaction? it is not balanced. a new compound is formed. a change has occurred in a nucleus. a new element has been formed.

Need asap ‼️ 20 pts which gravitational force field diagram is drawn correctly? (answers in pictures below)