1. THE PASSIVE VOICE

2. PASSIVE VOICE A) Use of Passive
Passive voice is used when the focus is on the action. It is not important or not known who or what is performing the action.
Example: My bike was stolen.
In the example above, the focus is on the fact that my bike was stolen. I do not know, however, who did it.

3. Sometimes a statement in passive is more polite than active voice, as the following example shows:
Example: A mistake was made.
In this case, I focus on the fact that a mistake was made, but I do not blame anyone (e.g. You have made a mistake.).

4. B) Form of Passive
Subject + to be + Past Participle (3rd column of irregular verbs)
Example: A letter was written.
When rewriting active sentences in passive voice, note the following:
object of the "active" sentence becomes subject in the "passive" sentence.
subject of the "active" sentence becomes "object" in the "passive" sentence" (or is left out) 

5. EXAMPLES Active: Peter builds a house. Passive: A house is built
by Peter.

6. SIMPLE PRESENT Active Peter builds a house. Simple Present Passive:
Passive:
A house
is built
by Peter.
SIMPLE PRESENT

7. SIMPLE PAST Active: Peter built a house. Simple Past Passive: A house
Passive:
A house
was built
by Peter.
SIMPLE PAST

8. SIMPLE FUTURE Active: Peter will build a house. will-future Passive:
Passive:
A house
will be built
by Peter.
SIMPLE FUTURE

9. MODAL VERBS Active: Peter can build a house. Modals Passive: A house
Passive:
A house
can be built
by Peter.
MODAL VERBS

10. C) Active sentences with two objects in passive
When there are two objects in an active sentence, there are two possible active sentences and two possible passive sentences.
possibility 1:
The professor explained the students the exercise. possibility 2:
The professor explained the exercise to the students.
There are two objects in each of the following sentences: object 1 = indirect object: the students object 2 = direct object: the exercise
An indirect object is very often a person, a direct object a thing. When a direct object is followed by an indirect one, we put to in front of the indirect object.

11. Each of the objects (direct and indirect) can be the subject in the passive sentence.
passive sentence - possibility 1
subject
verb
object
(by-agent)
The students
were explained
the exercise.
(by the professor).
passive sentence - possibility 2
subject
verb
object
(by-agent)
The exercise
was explained
to the students
(by the professor