Se usa la voz pasiva para dar énfasis a lo que fue hecho, en vez de dar énfasis a la persona que hizo algo.

Ejemplo:  

Un mecánico pintará el coche.

A mechanic will paint the car.

(voz activa)

El coche será pintado por un mecánico

The car will be painted by a mechanic

 (voz pasiva)

5 sentences in Present

A letter is written by Kris.

A hot dog is eaten by him.

The tire is changed by Abel.

A movie is going to be watched by us tonight.

The students’ questions are always answered by the teacher.

5 sentences in Past

A letter was written by Kris.   

The novel was read by Mom in one day.

The video was posted on Facebook by Alex.

The baby was carried by the kangaroo in her pouch.

The tire was changed by Abel.

5 sentences in Future

A letter will be written by Kris.

The house will be cleaned by me every Saturday.

The victory will be celebrated by the team tomorrow.

A safety video will be watched by the security every year.

A movie will be watched by us tonight.

5 sentences in Present perfect

A hamburger has been eaten by me.

The present has been opened by me.

A letter has been written by Kris.

The house has been cleaned by me every Saturday.

The baby has been carried by the Kangaroo in her pouch.

Kris A.