Final answer:
When an electric charge is shaken at a high frequency, it emits light in the form of electromagnetic waves. This occurs due to the rapid oscillation of charge, creating a changing electric and magnetic field pattern. Sound is not emitted, as it requires a medium to travel and is a result of mechanical vibrations.
Step-by-step explanation:
If an electric charge is shaken up and down frequently enough, what can be emitted is light. When electric charges oscillate with enough frequency, they can produce a changing pattern of electric and magnetic fields that spread out and move rapidly through space. This phenomenon, as described by Maxwell's equations, refers to the generation of electromagnetic waves, which we perceive as light.
The waving or shaking of charges in a certain frequency range emits electromagnetic radiation, while sound requires a medium to travel through and is a mechanical wave resulting from vibrations within that medium. Therefore, the correct answer to the posed question is 2) Light.
Shaking a piece of metal with free electrons does not cause the electrons to fall out because the energy involved in the shaking process is not typically enough to overcome the forces that hold the electrons within the metal. In contrast, when metal is heated to a high temperature, the thermal energy can provide enough energy for the electrons to escape, a phenomenon known as thermionic emission.
The distribution of energy in heating is such that it can increase the kinetic energy of the electrons enough to allow them to overcome the attraction of the positively charged ions in the metal and be boiled off.
Therefore, the correct answer to the posed question is 2) Light.