Adjective clauses are dependent clauses used to modify nouns or pronouns. An adjective clause usually immediately follows the noun or pronoun it modifies (see Misplaced Modifiers). A common type of adjective clause is the relative clause. As with other modifiers, punctuation with adjective clauses is determined by whether the clauses are restrictive or nonrestrictive.
A relative clause is an adjective clause introduced by a relative pronoun, which joins the clause to some word in the main clause. Relative clauses are useful linking devices, since they allow two pieces of information about a noun or pronoun (the information in the main clause and the information in the relative clause) to be conveyed within a single sentence, without repetition of the noun or pronoun.
The development of transistors was made public in 1948 by demonstrating radio and television sets whose vacuum tubes had been replaced by transistors.
You can turn a sentence into a relative clause by changing a noun or phrase in the sentence into a relative pronoun and reordering the clause, if necessary, so that the relative pronoun becomes the first word in the clause.