The word get and become are sometimes interchangeable. However, get has several different meanings. Become, on the other hand, is mainly used to talk about a development of some kind.
Get is one of the commonest words in English. It is mainly used in informal English. Some people even believe that get should not be used in formal speech and writing. That probably doesn’t make much sense, though.
Get/become + adjective
Both get and become can be followed by adjectives. In this case, they both indicate growth or development of some sort.
Compare the following sentences.
She got angry when she realized that he was lying. (Informal)
She became angry when she realized that he was lying. (Formal)
I got / became interested in classical music when I was in high school.
As I get older I get more optimistic.
As I become older I become more optimistic.
It got colder and colder the higher we climbed.
It became increasingly cold as we climbed higher.
Become + noun
Get cannot be used with a noun to indicate development or change. In this case, only become is possible.
She became a nun. (BUT NOT She got a nun.)
Get + noun/pronoun
When get is followed by a noun or a pronoun, it means ‘obtain’, ‘fetch’, ‘receive’ or ‘acquire’. Become cannot be used with this meaning.
I got a call from Betty. (= I received a call from Betty.)
She gets $300 a week. (= She earns $300 a week.)
Could you get me a glass of water? (= Could you fetch me a glass of water?)