active voice- present tense: I am shopping at the mall.
passive voice-present tense: The paintings are bought by the highest bidder.
active voice-past tense: I bought a pair of shoes.
passive voice-past tense: The class last year was full of smart students.
First three examples are good, the last is ambiguous.
Sentences where the main verb is a form of “to be” (e.g., is, am, are, was, were, be, being, been, etc.) are neither active nor passive. Even the “the class last year was filled with smart students” is ambiguous: you really can’t tell whether “was filled” is a compound verb, or whether “filled” is just a participial adjective describing “the class”. Notice that the ambiguity goes away in a different context, even if the same verb is used:
past passive: “The car was filled at the gas station.” In this case “was filled” clearly emphasizes the action of putting gas in the car, not the state of the car afterward.