Passive Voice

 Verb forms:

 Present simple am/are/is + past participle

Past simple was/were + past participle
 Present continuous am/are/is + being + participle

 Past continuous was/were + being +participle

 Present perfect have/has been + participle

Past perfect had been + participle
Future simple will be+participle

Going to am/are/is + going to be + participle

Modal verb modal verb + be + participle

Infinitive (to) be + pp OR (to) have been + participle

He writes a book	A book is written
He is writing a book	A book is being written
He wrote a book	A book was written
He was writing a book	A book was being written
He has written a book	A book has been written
He had written a book	A book had been written
He will write a book	A book will be written

We use the passive voice when who or what causes the action is unknown or unimportant or obvious or 'people in general':

• He was arrested (obvious agent, the police).
• My bike has been stolen (unknown agent).
• The road is being repaired (unimportant agent).
• The form can be obtained from the post office (people in general). 

In  factual or scientific writing:

• The chemical is placed in a test tube and the data entered into the computer.

Here's a list of exercises for practice with the passive