The vibration of the strings when struck, plucked or strummed is responsible for the sound of a guitar. However, if these strings alone vibrate themselves, they will not produce a loud sound. This is where the body of the guitar plays the role.
When a string vibrates by itself, It only makes a little contact to air molecules thus, does only produce a soft sound. But when it is connected to a solid object (the body of the guitar in this matter) it disturbs more air and the air vibrates back from the string to the body to the string again depending on how hard you pluck the string.
The hollow body of the guitar makes the sound fuller and keep its vibration to produce sounds that are good to hear.
The semi-acoustic and semi-hollow body guitars are generally praised for their warm tones. Semi-hollow guitars share some of the same characteristics as the hollow guitars. One of them is their clean tone, and hollow guitars are less durable. They do not amplify the sound. The guitar body has an electrical transformer or a transmission; it converts high-velocity low force to lower velocity, higher force.
Hollow guitars are notorious for producing a jangly sound that works well for jazz and blues music. The hollow-bodied guitars possess a much more acoustic sound, although they do tend to have higher levels of feedback.