The passive voice formed by Subject + verb to be+Past Participle. The object in the active voice becomes the subject of the passive voice and the subject of the active voice is either the object in the passive voice or is not mentioned.
The passive voice is used when we don't know the performer of the action. Example: “The house was built in 1884” in this case we don't know who built the house.
The passive voice is used when the focus is on the receiver of the action. Example: “Five people were killed in a car accident”, in this case the focus is on “five people”
The passive voice is used when the focus is on the action. Example: “The car was stolen”, in this case the emphasis is on the fact that the car was stolen and not on who stole it.
So the three options that apply to the uses of the passive voice are:
when the performer of the action is unknown
when you want to emphasize the action directly
when you want to emphasize the receiver of the action
